capacitor Related Articles

IntroductionCapacitors are components that store electricity and electrical energy (potential energy) and play an important role in circuits such as tuning, bypassing coupling, and filtering. Capacitors are connected in parallel to increase capacity, and capacitors are connected in series to decrease capacity. When the capacitor is connected in series in the circuit, it can prevent the sudden change of voltage and absorb the overvoltage in the peak state. The series resistance plays a damping role, and the resistance consumes the energy of the overvoltage, thereby suppressing the oscillation of the circuit. When the capacitor is connected in parallel, the parallel resistor can absorb the electric energy of the capacitor, prevent the discharge current of the capacitor from being too large, and avoid damaging the devices (such as thyristors) connected in parallel with it. This is a very comprehensive article including the calculation formulas, circuits, and related common problems of series capacitors and parallel capacitors.Capacitors in Series & Parallel - Electronics BasicsCatalogIntroductionCatalogI What are the Capacitors in Series and Parallel?II Calculation Methods of Capacitance of a Series/Parallel Network  2.1 The Series and Parallel Combination  2.2 Voltage Division  2.3 How to Divide the Voltage When Capacitors are Connected in Series?  2.4 What is the Voltage Division Formula When Connecting 2 Capacitors in Series?III The Equivalent Method of Series or Parallel Connection of Capacitors with Different Rated Voltages and CapacitiesIV Comparison Table of Capacitors in Series and Parallel  4.1 Calculation Comparison of Capacitors in Series and Parallel  4.2 Correspondence Between Magnetic Circuit and Electric Circuit  4.3 Basic Physical Quantities of Magnetic Field and Magnetic CircuitV Frequently Asked Questions about Capacitors in Series and ParallelVI Electrolytic Capacitors in Series  6.1 Function and Purpose of 2 Electrolytic Capacitors in Anti-phase Series  6.2 Is the Electrolytic Capacitor in Series a Non-polarised Capacitor?VII QuizVIII FAQI What are the Capacitors in Series and Parallel?1.1 Parallel Connection of CapacitorsWe can describe the capacitors in parallel as a "water tank", but the water tank stores water, and the capacitor stores electric charges. If multiple capacitors are connected in parallel, they can naturally store more charge.(1) The equivalent capacitance after parallel connection is equal to the sum of the capacitance of each capacitance;(2) The voltage at both ends of each capacitor after parallel connection is equal;The withstand voltage after parallel connection is equal to the smallest capacitor voltage, and the equivalent capacitance is C1+C2, as shown in the figure below.Figure1. Parallel Connection of Capacitors1.2 Series Connection of Capacitors(1) The equivalent capacitance capacity after series connection is equal to the sum of the reciprocal of each capacitance;(2) The capacitance of each capacitor after series connection is equal;(3) The withstand voltage after series connection is equal to the sum of each capacitor voltage.After the capacitor is connected in series, it is equivalent to increase the distance between the two poles. The more the number in series, the smaller the capacitance, but the higher the withstand voltage. In actual circuit design, we generally rarely use capacitors in series, but capacitors in parallel are often used. Sometimes the capacity of a single capacitor is not enough, and one more is added.Figure2. Series Connection of CapacitorsII Calculation Methods of Capacitance of a Series/Parallel Network2.1 The Series and Parallel Combination(1) How to calculate the series capacitance of a capacitor?Suppose there are n capacitors connected in series. The series combination of these n capacitors is connected across a voltage source of V volts. Let us consider that the voltages across capacitors 1, 2, 3...n are V 1, V 2, V 3... Vn, respectively. The capacitances of capacitors 1, 2, 3 ... n are C 1, V 2, V 3 ... C n farad. Since all capacitors are connected in series, each of them will get the same charge, ie it is Q Coulomb. Now we know that the charge at both ends of the capacitor is only the product of the potential difference between the two ends of the capacitor and its capacitance value.Since the series combination of these capacitors is connected across the source of the voltage V volts, replacing the series combination n of multiple capacitors.If we consider a single equivalent capacitor of C,Now we get from equations 1 and 2,Therefore, when multiple capacitors are connected in series, the reciprocal of the equivalent capacitance of the system is given by the arithmetic sum of the reciprocal of their respective capacitances. (2) How to calculate the capacitance in parallel circuits?Suppose there are n capacitors connected in parallel. The parallel combination of these n capacitors is connected across the V volt voltage source. Since the capacitors are connected in parallel to the same voltage source, the charge of each capacitor is different and depends on their respective capacitance values. Let us consider that the charges of capacitors 1, 2, 3...n are Q 1, Q 2, Q 3,..., Q n coulombs, respectively. The capacitances of capacitors 1, 2, 3,..., n are C_1, C_2, C_3,... C_n coulombs respectively. It is now known that a charging capacitor is just the product of the voltage across the capacitor and its capacitance value. therefore,Now instead of connecting multiple capacitors in parallel, if we connect a single equivalent capacitor with capacitance C across the voltage source, then the total charge at both ends of the equivalent capacitor,Since all capacitors are connected in parallelWe can get from equations 1 and 2,Therefore, when multiple capacitors are connected in parallel, the capacitance of the system is given by the arithmetic sum of their respective capacitances.Figure3. (a) Three capacitors are connected in parallel. Each capacitor is connected directly to the battery.              (b) The charge on the equivalent capacitor is the sum of the charges on the individual capacitors. (3) Other related calculation formulasWhen the capacitor is connected in parallel, the area of the electrode is increased, and the capacitance is increased. The total capacity when connected in parallel is the sum of each capacity. When the capacitors are connected in series, the resistance value of the capacitor should be smaller than the insulation resistance of the capacitor in parallel to make the voltage distribution on each capacitor even, so as not to damage the capacitor due to uneven voltage distribution. The series and parallel calculations of capacitors are just the opposite of the series and parallel calculations of resistors.Voltage is the voltage during charging. The relationship between capacity and current, voltage is similar to power and is related to load.When voltage and capacity are quantitative, the smaller the load resistance, the larger the current and the shorter the time.When the voltage and load are quantitative, the larger the capacity, the longer the current and the longer the time.But in the actual discharge circuit, the general load is unchanged, the voltage of the capacitor is gradually reduced, and the current is gradually reduced. (1) Electric capacity (uf) = current (mA)/15Current limiting resistance (Ω)=310/maximum allowable surge currentDischarge resistance (KΩ)=500/capacitance (uf) (2) Calculation method C=15×IC is the capacitance of the capacitor, the unit is microfarad; the i device is the working current, the unit is ampere.For example, if the resistance of a bulb is 0.6 amps, the capacitance should be 15×0.6=9 microfarads, and a 9 microfarad capacitor in series is sufficient. (3) Empirical formula, 1uF output 50mA (if it is linear, a 10000F super capacitor can reach a surge current of 500 megaamps) (4) The calculation of the half-wave rectification method should provide about 30mA current per uF capacitance, which is a reference on the 50Hz220V line in China.The current is doubled in full-wave rectification, that is, 60mA current can be provided per uF.Formula: R*C≥(3～5)*T/2, you need to know the frequency of the lowest signal in the ripple component (that is, the maximum T), and then determine the value of C. ● Capacitor capacityCapacitor capacity indicates the size of electric energy that can be stored. The obstructive effect of capacitors on AC signals is called capacitive reactance. The capacitive reactance is related to the frequency and capacitance of the AC signal. The capacitive reactance XC=1/2πf c (f represents the frequency of the AC signal, and C represents the capacitance of the capacitor). ● The capacity unit and withstand voltage of the capacitor.The basic unit of capacitance is F (farad), and other units include: millifarad (mF), microfarad (uF), nanofarad (nF), picofarad (pF). Since the capacity of the unit F is too large, we generally see units of μF, nF, and pF. Conversion relationship: 1F=1000000μF, 1μF=1000nF=1000000pF. Each capacitor has its withstand voltage value, denoted by V. Generally, the nominal withstand voltage of the electrodeless capacitor is relatively high: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, etc. The withstand voltage of polar capacitors is relatively low. Generally, the nominal withstand voltage values ​​are: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V, etc. Power capacitor calculation: such as a three-phase capacitor bank with a nominal voltage of 690v and a capacity of 15kvar. Used in 600v circuit, delta connection, the actual effective capacity is: s=15kvar*600*600/(690*690)=11.34kvar. That is: the capacity and voltage are proportional to the square.2.2 Voltage DivisionDue to the large capacity of large capacitors, the volume is generally large, and they are usually made by multi-layer winding, which leads to a relatively large distributed inductance of large capacitors (also called equivalent series inductance, or ESL for short). The impedance of the inductor to the high frequency signal is very large, so the high frequency performance of the large capacitor is not good. Some small-capacity capacitors are just the opposite. Because of their small capacity, the volume can be made small (shortening the lead wire reduces the ESL, because a piece of wire can also be regarded as an inductance), and flat capacitors are often used Structure, such a small capacity capacitor has a small ESL so that it has a good high frequency performance, but due to the small capacity, the impedance to low frequency signals is large. So, if we want to pass the low frequency and high frequency signals well, we use a large capacitor and then a small capacitor.The commonly used small capacitor is 0.1uF CBB capacitor is better (ceramic capacitor is also OK), when the frequency is higher, you can also connect smaller capacitors in parallel, such as a few pF, hundreds of pF. In digital circuits, a 0.1uF capacitor is generally connected to the ground in parallel to the power pin of each chip (this capacitor is called a decoupling capacitor, of course, it can also be understood as a power filter capacitor, the closer the chip is, the better), because The signal in these places is mainly high-frequency signal, and it is enough to use a smaller capacitor to filter. The impedance of an ideal capacitor decreases as the frequency increases (R = 1/jwc), but an ideal capacitor does not exist. Due to the distributed inductance effect of the capacitor pins, the capacitor is no longer a simple capacitor in the high frequency range. , It should be regarded as a series high-frequency equivalent circuit of capacitance and inductance. When the frequency is higher than its resonance frequency, the impedance shows the characteristic of increasing with the increase of frequency, which is the inductance characteristic. At this time, the capacitance is like An inductance. On the contrary, inductors have the same characteristics. Large capacitors in parallel with small capacitors are widely used in power supply filtering. The fundamental reason is the self-resonance characteristics of the capacitor. The combination of large and small capacitors can well suppress low-frequency to high-frequency power interference signals. Small capacitors filter high frequencies (high self-resonant frequency), and large capacitors filter low frequencies (low self-resonant frequency). The two complement each other. ● Series voltage divider ratio: V1 = C2/(C1 + C2)*V...the larger the capacitance, the smaller the voltage divided, which is the same under AC and DC conditions● Parallel shunt ratio: I1 = C1/(C1 + C2)*I...The larger the capacitance, the larger the current that passes. Of course, this is under AC conditions.Explanation: When two or more capacitors are connected in series, it is equivalent to lengthening the insulation distance, because only the two polar plates on the two sides work, and because the capacitance is inversely proportional to the distance, the distance increases and the capacitance decreases; two or two When the above capacitors are connected in parallel, the area equivalent to the plate increases, and because the capacitance is proportional to the area, the area increases and the capacitance increases. ● Capacitors in series: After the capacitors are connected in series, the capacity decreases and the withstand voltage increases. Formula: 1C1+1C2=1C If two 50uf are connected in series, it becomes 25uf.● Withstand voltage = add the withstand voltage values ​​of two capacitors. If two 100V withstand voltages are connected in series, it becomes 200V.● The formula for calculating the capacity of the series circuit of the capacitor C: 1/C=1/C+1/C2+1/C3+.+1/CnC is the total capacitance value of the capacitor series circuit, C1, C2, C3, Cn are the capacitance values of each capacitor in the capacitor parallel circuit, that is, the reciprocal of the total capacitance of the series circuit is equal to the sum of the reciprocal of the capacitance of each capacitor in the series circuit.Figure4. Capacitors in Series and Parallel2.3 How to Divide the Voltage When Capacitors are Connected in Series?For example 4V voltage source, two capacitors of 0.5F and 1F in series. If it is a DC voltage source, according to the characteristics of capacitor series voltage division introduced in middle school physics:(1) The total voltage across the capacitor series circuit is equal to the sum of the divided voltages across the capacitors. That is, U= U1+ U2+ U3+…+Un.(2) When capacitors are connected in series, the voltage distributed on each capacitor is inversely proportional to its capacitance. That is, Un = Q / Cn (because in the capacitor series circuit, the amount of charge carried on each capacitor is equal, so the larger the capacitor, the lower the voltage, and the smaller the capacitor, the higher the voltage. .)Then the voltage source of 4V, the voltage on the two capacitors of 0.5F and 1F are 8/3V and 4/3V respectively 2. If it is an AC voltage source, from the impedance of the capacitor Xc=1/jωC, we can see |Xc| and C In inverse proportion, the same result can be obtained by using |Xc| as a resistor to calculate the voltage divider.2.4 What is the Voltage Division Formula When Connecting 2 Capacitors in Series?This is a theoretical calculation problem. It is necessary to assume that the withstand voltage value of the capacitor has no margin, that is, a capacitor of 200pF is breakdown when it exceeds 500V; a capacitor of 300pF is breakdown when it exceeds 900V.After adding 1000V voltage, the 200pF capacitor will withstand 600V voltage. Regardless of the capacitor's withstand voltage margin, the 200pF capacitor will break down; at this time, 1000V will all be added to the 300pF capacitor, which exceeds its withstand voltage, so it will breakdown. Calculation formula:If there are M capacitors connected in series, the actual voltage value Un of any capacitor Cn is:Un=U*C/Cn Among them: U is the total voltage; C is the total capacity of M capacitors in series.For two capacitors in series, the formula evolves into:Assuming that the total voltage is U, the voltages on C1 and C2 are U1 and U2 respectively, thenU1=C2*U/(C1+C2)U2=C1*U/(C1+C2)III The Equivalent Method of Series or Parallel Connection of Capacitors with Different Rated Voltages and CapacitiesThe equivalent method of using capacitors with the same rated voltage in series or in parallel is relatively simple and commonly used.Several capacitors with different rated voltages and different capacities are connected in series or in parallel, and the equivalent methods are different. Now give examples to illustrate. There are three capacitors C1: 220µF /10V C2: 100µF/25V C3: 10µF/100VCalculate their parallel and series equivalent values ​​respectively. (1) Parallel equivalent method1) Equivalent capacitanceC and = C1 + C2 + C3= 220µF + 100µF + 10µF/= 330µF2) Equivalent withstand voltageU parallel = U1 = 10V (take the minimum withstand voltage value U1) (2) Series equivalent method1) Equivalent capacitance1/C string ==1/C1 + 1/C2 + 1/C3= 1/220 + 1/100 + 1/10= 252/2200C string == 2200/252≈ 8 (µF)2) Equivalent withstand voltage ● Compare the Q value of each capacitorQ1= C1 X U1 Q2=C2 X U2 Q3=C3 X U3= 220 X 10 =100 X 25 =10 X 100=2200 (C) =2500 (C) =1000 (C)Q = Q3 =1000 (C) (take the minimum power value Q3) ● Find the actual allowable withstand voltage value of each capacitorU1 (actual) = Q/C1 U2 (actual) = Q/C2 U3 (actual) = Q/C3= 1000/220 = 1000/100 = 1000/10≈4.5(V) = 10 (V) =100 (V)3) U string = U1 (actual) + U2 (actual) + U3 (actual)≈4.5 + 10 + 100≈114.5(V)Figure5. Equivalent CapacitanceIV Comparison Table of Capacitors in Series and Parallel4.1 Calculation Comparison of Capacitors in Series and Parallel4.2 Correspondence Between Magnetic Circuit and Electric Circuit4.3 Basic Physical Quantities of Magnetic Field and Magnetic CircuitV Frequently Asked Questions about Capacitors in Series and Parallel(1) Do capacitors charge faster in parallel or series?If two capacitors with the same capacity are connected in parallel or in series in the same circuit, the capacitor in series will charge faster, because the capacity of the capacitor is reduced by half after the capacitor is connected in series, and the charging time becomes shorter. The capacity of the capacitor after parallel connection is doubled, and the charging time will be longer for the same charging circuit. (2) The electric charge of each capacitor in the series circuit is equal. Why is the electric charge of each capacitor equal to the electric charge of the equivalent capacitor?Capacitor voltage: U=Q/CQ=I*tSo U=(I*t)/CWhen the capacitors connected in series are connected to the power supply, the capacitors start to charge. The current flowing through each capacitor is the same. As time goes by, the voltage of each capacitor increases. However, due to the different voltage rise rates of C, the sum of the voltage of each capacitor is equal to the power supply. When the voltage is applied, charging stops and the current is zero. Analyze this process: the current flowing through each capacitor during the entire charging process is the same, and the elapsed time is the same, so the current of each capacitor is the same over time, so the amount of charge is the same and equal to the capacity of the capacitor.Figure6. A Charging State of Three Capacitors in Parallel(3) Are the filter capacitors in the power amplifier power supply connected in parallel?The filter capacitor of the power amplifier power supply is set to eliminate some of the AC components contained in the rectification from AC to DC (the purpose is to improve the audio quality), so all capacitors with larger capacity are selected, generally using electrolysis above tens of microfarads Capacitor. The parallel connection of capacitors is the addition of the capacity of each capacitor, usually forming a standard type 1 filter circuit: "capacitor-resistor (or inductance)-capacitor". If the capacitors are connected in series, the capacity will decrease, it will only increase the cost and occupy more space, meaningless. The power supply line filter capacitor of the amplifier circuit of the power amplifier is generally grouped in parallel. Depending on the design of the power supply, the single power supply circuit may also be directly connected in parallel, or divided into two groups. The two groups are separated by power inductors or resistors into two filter circuits to form a pie-type filter circuit; if it is a dual power supply circuit, , It is generally divided into two groups as for the two groups of power lines. The easiest way to increase the filter capacitor of the power amplifier is to see the positive and negative poles and the rated withstand voltage. Connecting them in parallel can improve the stability of the DC voltage and improve the low-frequency characteristics of the amplifier, making the low frequency of the speaker sound more full and round. Capacitors are generally used in parallel, and capacitors of different capacities filter noise at different frequencies. Large-capacity capacitors can only be realized by electrolytic capacitors. Electrolytic capacitors have positive and negative polarity and are very loud when connected reversely.VI Electrolytic Capacitors in Series6.1 Function and Purpose of 2 Electrolytic Capacitors in Anti-phase SeriesIn some circuit designs, it is seen that two electrolytic capacitors are connected in series in the reverse phase. The capacity of the two components should be equal and the withstand voltage is the same. In AC circuits, the leakage current can be reduced. Just use a non-polar capacitor to get a large-capacity non-polar capacitor. . Large-capacity non-polar capacitors are more expensive. The electrolytic capacitor has a large capacity and is cheap, but it has a polarity, and the two are connected in reverse series. It is non-polar. It can only be used in very low voltage applications (up to 1-2V). The voltage is slightly higher. When the capacitor is used in the opposite direction, the leakage will be large. The accumulated effect will cause the electrolytic capacitor to heat up and eventually cause the capacitor to explode. Electrolytic capacitors are used in DC circuits. So its series connection should be the negative pole of the first one and the positive pole of the second (just like dry batteries in series). But in the circuit, there is indeed a case where the negative poles of two electrolytic capacitors are connected to the negative pole (inverted series), and the two positive poles are used. This is because it is used in an AC circuit (in a circuit where DC and AC coexist), There is no guarantee that the potential of one pole is always higher than the other pole), so that when the capacitor is under reverse voltage, serious leakage current will be generated. At this time, non-polar capacitors should be used, but non-polar capacitors are expensive and expensive. The volume is large, so some people use two electrolytic capacitors to "reverse series".  Its working state is that when there is alternating current, one of them is in the reverse state. Due to its serious leakage, the voltage drop across it is very small. Almost all of the voltage falls on the positive capacitor, and when the other half cycle of the alternating current, the state of the two capacitors will be exchanged, so these two capacitors are used as one, and the total capacitance is equal to any one of them. The total withstands voltage value is equal to 2 times of any capacitor.6.2 Is the Electrolytic Capacitor in Series a Non-polarised Capacitor?Of course, two electrolytic capacitors in parallel will not work. If two electrolytic capacitors are connected in series, it will still not work without applying a proper bias voltage. Applying a bias voltage is quite complicated, especially when both ends of the capacitor (two in series) are not grounded (the bias voltage must be floating). Considering the complexity of applying the bias voltage, it is better not to use this method: connect the negative poles of the two capacitors, and connect the two capacitors in parallel with a high-current diode. The positive of the diode is connected to the negative of the capacitor, and the negative is connected to the positive of the capacitor. Parallel connection of course still has polarity. If reverse parallel connection, it is non-polar, but it is non-polar. Reverse series connection is also not advisable. If you do a test, you will find that there must be a capacitor that withstands the backpressure. If the voltage is large, it will blow up. Unless special measures are taken, the voltage is always applied to the capacitor with the positive voltage. on. Two electrolytic capacitors of the same capacity can be connected in series, but a diode must be connected in anti-parallel to prevent the reverse breakdown of the electrolytic capacitor. After adding a diode, it is okay if it is used for filtering, but it is definitely not good for blocking DC. Because the electrolytic capacitor is only charged and not discharged. Two identical electrolytic capacitors connected in reverse series can replace non-polar capacitors with the same capacity. The dielectric loss of the electrolytic capacitor is very large, and it must be connected to the AC circuit after the voltage is greatly reduced. Otherwise, it is either burned or fried.VII Quiz● QuestionA network of five capacitors of C is connected to a 100 V supply, as shown below figure. Determine(a) the equivalent capacitance of the network(b) the charge on each capacitor. ● SolutionIn the given network, the top three Capacitance is in series, So equivalent capacitance of the top part1C1=1C+1C+1CC1=C3Similarly, the lower two Capacitance is in series, So equivalent capacitance of lower part1C2=1C+1CC2=C2 Now both C1 and C2 are in parallel, so equivalent Capacitance of the NetworkCeq=C1+C2=C3+C2=5C3Now Charge on top part will beQ1=C1V=CV3Now Charge on lower part will beQ2=C2V=CV2  VIII FAQ1. How do you solve capacitors in series and parallel?To calculate the total overall capacitance of a number of capacitors connected in this way you add up the individual capacitances using the following formula: CTotal = C1 + C2 + C3 and so on Example: To calculate the total capacitance for these three capacitors in parallel. 2. How do you know if a capacitor is in series or parallel?In your circuit current, all of the current going to one capacitor must also go to the other. Therefore they are in series. Hope this helps. If two (two-terminal) circuit elements are series-connected, they have identical (not just equal) currents through. 3. What is a capacitor in parallel?Capacitors are connected together in parallel when both of their terminals are connected to each terminal of another capacitor. The voltage ( Vc ) connected across all the capacitors that are connected in parallel is the same. 4. Can you put two capacitors in series?If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacings of the individual capacitors. With resistors, series connections result in additive values while parallel connections result in diminished values. 5. How are capacitors connected in series?Here are the rules for calculating capacitances in series: If the capacitors are of equal value, you're in luck. All you must do is divide the value of one of the individual capacitors by the number of capacitors. For example, the total capacitance of two, 100 μF capacitors is 50 μF. 6. Why capacitor is connected in parallel?Capacitors are devices used to store electrical energy in the form of electrical charges. By connecting several capacitors in parallel, the resulting circuit is able to store more energy since the equivalent capacitance is the sum of individual capacitances of all capacitors involved. 7. Do capacitors in series increase voltage?Capacitors connected in series will have lower total capacitance than any single one in the circuit. This series circuit offers a higher total voltage rating. The voltage drop across each capacitor adds up to the total applied voltage. This is why series capacitors are generally avoided in power circuits. 8. Do capacitors in series or parallel store more energy?The energy stored in a capacitor is a function of the voltage across the capacitor. The voltage will be higher when they are in parallel, so the parallel connection stores the most energy. 9. Why voltage is different in a series combination of capacitors?In a series combination, since the charge stored is the same as the same charge flows through all the capacitors, the potential difference across each will be different. 10. When capacitors are wired in parallel what must be the same for the two capacitors?The charge in the two capacitors is different. Capacitors connected in parallel are connected to the same start and end points of the input and output that's why they have the same potential difference.  

IntroductionWhat is the difference between a three-phase AC motor and a single-phase AC motor? If you pay attention to it, you will find that single-phase AC motors have more equipment than three-phase AC motors, which is the start capacitor (starting capacitor). The most common one is in various household appliances. Almost all household appliances with motors are equipped with start capacitors. This article will start with the explanation of the principle of the motor start capacitor, and then describe in detail the failure phenomena, causes and test methods of the start capacitors in the two common home appliances, air conditioners and fans. In addition, the article will also explain some basic questions about start/run capacitors. If you want to learn the related knowledge of motor start capacitors, this article must be worthy of your reading.How to test a RUN or START CAPACITOR the CORRECT wayCatalogIntroductionCatalogI The Principle and Causes of Damage of Start Capacitor 1.1 How Does the Motor Work? 1.2 How Does the Start Capacitor Work? 1.3 Reasons for the Burning of the Start CapacitorII Troubleshooting of Start Capacitor in Air Conditioner 2.1 Functional Characteristics of Start Capacitor 2.2 How to Quickly Figure out Whether the Start Capacitor is Damaged 2.3 Why is the Start Capacitor of the Air Conditioner Outdoor Unit Easy to Damage? 2.4 Symptoms and Test MethodsIII How Test the Motor Start Capacitor of a Fan?IV Relevant Knowledge in the Step of Start Capacitor Test 4.1 How to Choose Start Capacitor? 4.2 Precautions for Replacing the Start CapacitorV How to Test the Motor Start Capacitor without a MultimeterVI Frequently Asked Questions about Start Capacitors 6.1 Which Motors are Served by the Start Capacitor? 6.2 Why Does a Three-phase Motor do not Need a Start Capacitor? 6.3 The Relationship Between Start Capacitors and Motor 6.4 What are the Functions of Start Capacitors, Run Capacitors, and Centrifugal Switches in Single-phase Motors?VII QuizⅧ FAQI The Principle and Causes of Damage of Start Capacitor1.1 How Does the Motor Work?The single-phase current flowing through a single-phase motor cannot generate a rotating magnetic field, and a capacitor is needed to separate the phases. The purpose is to make the current in the two windings produce a phase difference of nearly 90 ゜ to generate a rotating magnetic field. The capacitive induction motor has two windings, namely the starting winding and the running winding. The two windings are 90 degrees apart in space. A large-capacity capacitor is connected in series to the starting winding. When the running winding and the starting winding pass single-phase alternating current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, thus reaching the maximum value first. Two identical pulsed magnetic fields are formed in time and space so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the motor rotor, and the current interacts with the rotating magnetic field. The electromagnetic field torque causes the motor to rotate.Figure1. Electric-Motor1.2 How Does the Start Capacitor Work?A single-phase power supply is different from a three-phase power supply in that a three-phase rotating magnetic field is generated in the motor. The principle of capacitor starting of single-phase motor is: using the principle that the current of the capacitor in the circuit is advanced by 90 degrees so that a magnetic field of 90 degrees ahead of the main winding is generated in the starting winding so that there will be an alternating 90-degree angle in the motor. The magnetic field, to put it plainly, uses the phase-shifting principle of the capacitor to transform a single-phase power supply into a two-phase power supply of 90 degrees to each other, and a rotating magnetic field of 90 degrees to each other is generated in the motor. Maybe it is easier to understand to explain from this aspect. The start capacitor is to give the motor a thrust when the motor is started so that the motor can turn from moving to rotating. Without it, when a single-phase AC motor starts, it will shake at the origin instead of rotating; the start capacitor is a two-phase AC motor, so the magnetic field cannot exert force on the rotor without it, and of course, it is impossible to rotate.Figure2. Capacitor Start Run Induction Motor1.3 Reasons for the Burning of the Start CapacitorGenerally, the start capacitor is not easy to burn, because its working time is very short, and it is thrown off by the centrifugal switch at the moment of starting, with no current flowing through the start capacitor. However, not easy to burn does not mean that it will never burn. If the start capacitor burns out, the possible reasons are as follows:① Capacitors have low voltage resistance or poor quality, so it is best to use capacitors with a voltage resistance of 500V. ② The centrifugal switch will often produce an arc when it is turned off. It is possible to burn the switch to the motor. After the switch is started, the switch cannot be turned off. There is always current through the capacitor. It is easy to burn the secondary winding of the motor and the start capacitor within a certain period of time. ③ The capacity of the selected capacitor is too small, and the starting current exceeds the allowable value of the capacitor. ④ The motor is bored or the bearing is damaged. It is difficult for the motor to start the centrifugal switch within a certain period of time and it is difficult to reach the disconnected speed, and the start capacitor is easy to burn.Figure3. Deteriorated CapacitorII Troubleshooting of Start Capacitor in Air Conditioner2.1 Functional Characteristics of Start CapacitorThe start capacitor is an important part of the auxiliary compressor to start. The capacitor is a large-capacity capacitor (1~6uF), which is used to provide starting current for the auxiliary winding of the motor to assist the compressor to start. The start capacitor is generally fixed on the bracket or support plate above the compressor, and the pin is connected to the starting end of the compressor.2.2 How to Quickly Figure out Whether the Start Capacitor is DamagedFirst of all, it depends on what kind of capacitors are used in electrical parts.● If the compressor start/run capacitor is damaged, the compressor cannot start or run intermittently.● If the capacitor of the fan motor is damaged, some malfunctions such as excessive exhaust temperature, excessive exhaust pressure, compressor overload, and small air output will occur during the operation of the air conditioner.2.3 Why is the Start Capacitor of the Air Conditioner Outdoor Unit Easy to Damage?The capacitor of the air conditioner compressor is installed in the outdoor unit. Due to the high temperature of the outdoor unit (ambient temperature + temperature emitted by the condenser), capacitors that have been used for a long time will easily dry up and fail the electrolyte.When replacing capacitors, be sure to use high-quality capacitors. The capacity must be the same, and the withstand voltage must not be lower than the original standard.Figure4. Air Conditioner Outdoor Unit2.4 Symptoms and Test Methods① Smoke.② Cannot operate normally.③ The display cannot be displayed normally.④ The power supply cannot be charged and discharged normally.⑤ Can not heat normally.⑥ The power factor compensates the capacitor damage, resulting in a waste of electricity. Different symptoms of damage to compressor start capacitor and external motor start capacitor:There are two capacitors in the outdoor electromechanical packaging, the larger one is the compressor capacitor, and the smaller one is the external motor capacitor. Different capacitors have different failure phenomena. ① Compressor capacitor damagethe performance phenomenon is that normal compressor startup will be accompanied by loud noise and jitter. If the capacitor is damaged, you will feel a slight jitter in the compressor by pressing the casing above the compressor, and the sound is like the sound of current passing. The compressor will stop running after a period of time. ② The damage of the external motor capacitorAfter the compressor is working normally, the external motor stops working for a period of time. If there is a fault code, there will be high-pressure protection and compressor exhaust pipe temperature protection.Figure5. Basic Electrical Controls of Air-Conditioning UnitsTest methods of air conditioner start capacitor● Method 1:The start capacitor of the air-conditioning compressor is a large-capacity electrolytic capacitor. When testing, using the capacitance setting of the digital multimeter to determine whether there is any abnormality.Under normal circumstances, the capacitance of the capacitor used to detect the capacitance of a multimeter should be the same or very close to the nominal capacitance, otherwise, the start capacitor is mostly deteriorating, such as dry electrolyte, leakage, etc., which should be replaced. ● Method 2:In addition to using a multimeter to test its capacitance, the ohmic setting of a pointer multimeter can also be used to test the charge and discharge performance of the start capacitor.Steps:① Connect the red and black test leads to the two poles of the compressor start capacitor.② The multimeter gear is set in ohm gear.③ Under normal circumstances, the pointer of the multimeter first swings to the right to a position, then slowly swings to the left, and finally stops at a fixed position.④If the pointer does not swing or the swing range is small, it indicates that the performance of the compressor start capacitor is poor.Suggested Reading: 5 Ways to Test Capacitors How to replace the start capacitor?If it is ensured that the air conditioner failure is caused by the damage of the compressor start capacitor itself, the damaged compressor start capacitor needs to be replaced. Replacing the start capacitor can generally be divided into three steps: removing the start capacitor, finding a replaceable start capacitor, and replacing the start capacitor. ①Remove the start capacitorThe compressor start capacitor is located on the circuit support board above the compressor. When disassembling, unplug the connecting wire and use a screwdriver to remove the fixing screw of the snap ring. ② Looking for replaceable capacitorsAfter removing the damaged compressor start capacitor, then select a suitable new start capacitor to replace it according to the specifications and volume of the damaged start capacitor.The specific content of how to select the start capacitor will be explained in detail below. ③Replace the start capacitorAfter selecting the compressor start capacitor, install the new compressor start capacitor in the outdoor unit, fix the metal fixing ring, reconnect the connecting cable, and then power on and test the machine to complete the replacement.Figure6. Motor Start CapacitorIII How Test the Motor Start Capacitor of a Fan?①Connect all parts on the circuit board of the air conditioner completely.②Turn on the power supply.③Use the remote control to adjust the temperature to make the fan motor rotate.④Connect the ground terminal of the oscilloscope probe to the ground terminal of the circuit board.⑤Use an oscilloscope probe to detect the white lead on the Hall element plug.⑥The oscilloscope shows signal waveform. When testing the start capacitor of the fan motor, a multimeter should be used to measure the resistance of the capacitor. Due to the large size of the capacitor, it is impossible to use the capacitor input jack for testing. At this time, you can use the multimeter pen to test and judge the quality of the capacitor by the change of the value displayed by the multimeter. If the resistance value displayed by the multimeter changes from small to large and then changes to infinity, it means that this is a good capacitor with charging and discharging functions. Check again after changing the test leads, the displayed value still changes from small to large, and changes to infinity. After measuring the capacitor, if the test leads are not replaced when the test is performed again, and the resistance value is displayed as infinite, it means that charging and discharging are not performed, but it does not mean that the capacitor is damaged. Therefore, when testing the capacitance, the test leads must be replaced no matter which multimeter is used.Figure7. Fan MotorRelated recommendation: How to Test Ceramic Disc Capacitor IV Relevant Knowledge in the Step of Start Capacitor Test4.1 How to Choose Start Capacitor?● How to calculate the starting and running capacitance of a single motorrun capacitance C=120000*I/2.4*f*U*cosφWhere: I is current; f is the frequency; U is the voltage; cosφ is the power factor, taking 0.5 to 0.7. The run voltage of the run capacitor is greater than or equal to (2～2.3) U.Start capacitor capacity = (1.5 ~ 2.5) run capacitor capacity.The run voltage of the start capacitor is greater than or equal to 1.42 U.(It is best when the voltage across the capacitor is 311V during operation) The working capacitor is 1-4UF per 100W, and the start capacitor is 4-10 times the working capacitor (the motor requires a larger starting torque). Empirical data, if your motor does not exceed 200W, the start capacitor will not exceed 100uF. If you run the capacitor, you can choose several values for the power-on test, and see which capacitor has the smallest current in the whole machine, then the capacity of the capacitor is the most Good value.) The capacity of the single-phase split-phase motor capacitor can be calculated by the empirical formula C=35000I/2PUfcos&Such as I=250W/220V=1.2AC=35000x1.2/2x1x50x220X0.8=24ufCan choose 350V30uf capacitance.Figure8. Starting Capacitor Table ● How to calculate the voltage across the run capacitor of a single-phase motor?① First of all, you must know the impedance value of the secondary winding. You can measure the resistance value by measuring the DC resistance with a multimeter. Then, the secondary winding is connected to a 12V AC voltage and the current value is measured. According to the winding impedance equal to the resistance and reactance in series, it can be calculated by phasor Out the winding inductance value. ② In normal operation, the capacitor is connected in series on the secondary winding, that is, the three equivalent parameters of winding resistance, winding reactance, and capacitance are connected in series and then connected to 220V voltage. It is easy to calculate the phasor according to the formula of the series circuit. Calculate the voltage on the capacitor. ③ When a single-phase motor is running, the voltage at both ends of the capacitor is generally above 300VAC, so the capacitor voltage is generally selected for a capacitor with a withstand voltage of 400V or more, and a capacitor with a voltage of more than 450V is better. ④ For the calculation of the capacitance withstand voltage, please refer to Article 2. First, measure the resistance R and reactance XL of the secondary winding, and then select the capacitance C according to the power of the motor to calculate the capacitive reactance Xc.The actual voltage across the capacitor during operation: Uc= Xc*220/(R+jXL-jXc); the withstand voltage value of the capacitor: Uce=1.3~1.5Uc.Figure9. Single Phase Motor Starting ● Detailed selection guide of start capacitor and run capacitorSingle-phase motor capacitor selection.Withstand voltage formula: U (capacitance) is greater than or equal to 1.5*USingle-phase run capacitor formula: C=1950×I/U×cosφ (using a capacitor, which is both a start capacitor and a run capacitor, is commonly used for small-capacity motors such as electric fans and washing machines)Start capacitor capacity formula: C=3500*I/U*cosφ (a capacitor is only used when starting, disconnected during normal operation, and switched with a transfer switch or a centrifugal switch.Dual-value capacitor run capacitor capacity formula: C=1200*I/U*cosφ (use 2 capacitors, one for operation and one for startup)Dual-value capacitor start capacitor capacity formula: C=(2～3)*C (run capacitor) C: Capacitor capacity: I: motor rated current, U: motor rated voltage, cosφ: power factor 0.7.Generally, there is no need to calculate. The run capacitor is 2~3μF per 100W, and the start capacitor is 2~3 times the run capacitor. The capacitor selection of the motor has strict requirements on the voltage, and it must be equal to or greater than 1.5 times the rated voltage of the motor. For a power supply with a rated voltage of 220V, the rated voltage of the capacitor cannot be lower than 400V. The capacitance value has a certain broadness, it doesn't matter if it is larger or smaller, especially the start capacitor, which can be selected at 2-6 times the working capacitor. ● How to choose the capacitor of single-phase asynchronous capacitor start the motorWe can calculate according to the following formulaPhase start capacitor capacity:C=350000*I/2p*f*U*cosφIn the formula: I---current;f-frequency;U---voltage;2p-the larger power factor is 2, and the smaller power factor is 4; cosφ---power factor (0.4～0.8).Split-phase start capacitor withstand voltage:The capacitor withstand voltage is greater than or equal to 1.42*U. Run capacitor capacity:C=120000*I/2p*f*U*cosφIn the formula: I---current;f-frequency;U---voltage;2p-take 2.4;cosφ---power factor (0.4～0.8). Run capacitor withstand voltage:The withstand voltage of the capacitor is greater than or equal to (2～2.3)*U.start capacitor capacity of double-value capacitor motor:C=(1.5～2.5)*operating capacitor capacity.Withstand voltage of start capacitor:The capacitor withstand voltage is greater than or equal to 1.42*U.4.2 Precautions for Replacing the Start CapacitorThe start capacitor is an important part of the electronic circuit. Once the start capacitor is broken, the motor cannot be started. The damaged start capacitor will only make a buzzing sound when it is energized for a short time, causing the current to surge, and long-time energization will cause severe overheating and even burn the motor, so it should be replaced immediately. And it is not difficult to judge that the start capacitor is broken. Most of the damaged start capacitors are bulging, and the surface will be burnt due to excessive current, and the rotor speed will be slow and weak. Of course, the most intuitive and accurate way is to use the capacitance setting of a multimeter to measure the quality. Once we have confirmed that the start capacitor has failed, the things that should be noted when replacing the start capacitor:① After the start capacitor is discharged, there will still be part of the residual charge that cannot be discharged for a while, and an artificial discharge should be performed again. ② Since the failed start capacitor may have poor lead contact, internal disconnection or fuse blown, etc., part of the charge may not be discharged. Therefore, the maintenance personnel should wear insulating gloves before touching the failed start capacitor. Using the short-circuit wire to short the two poles of the faulty capacitor first, and then it can be removed and replaced by hand. ③ If multiple start capacitors are used in series, they should be discharged separately.Figure10. Replace the Start Capacitor④ When handling or replacing a malfunctioning start capacitor, disconnect the power supply of the start capacitor, disconnect the switch or unplug the plug, and discharge the start capacitor. ⑤ When discharging, first connect the grounding terminal of the grounding wire, and then use the grounding rod to discharge the start capacitor several times until there is no discharge spark or discharge sound, and then fix the grounding terminal. ⑥ It should also be noted that general users often ignore the instruction manual, and the precautions for use must be carefully understood and followed during installation. As we all know, the impedance of a capacitor is inversely proportional to frequency. As the frequency increases, the loss also increases. Measures should be taken to limit the harmonics and inrush current in the circuit. Capacitors always generate heat, so pay special attention to ventilation and cooling. After the reactive power compensation device is installed, during the trial operation, the system should be tested, and measures should be taken in time if over-voltage, over-current, oscillation, and harmonics are found, which is very necessary for the normal operation of the capacitor. V How to Test the Motor Start Capacitor without a MultimeterA DC voltmeter can be connected to the capacitor in parallel, and an insulating shaker can be used to charge the capacitor (note the + and-poles)(1) See if the voltage can rise to the rated voltage of the capacitor:① 0V, the capacitor is short-circuited.② Slowly rise to the rated voltage of the capacitor, it proves that the capacitor is good.③ Raised quickly to the rated voltage of the capacitor, and the insulation resistance is about the internal resistance of the DC voltmeter, then the capacitor is open.(2) When it is stable at the rated voltage value of the capacitor, look at the insulation resistance of the capacitor:①The insulation resistance is close to the internal resistance of the DC voltmeter, so the capacitance is good.②If the insulation resistance is less than the internal resistance of the DC voltmeter, it means that the leakage of the capacitor is large, and it is easy to generate heat and cannot be used.VI Frequently Asked Questions about Start Capacitors6.1 Which Motors are Served by the Start Capacitor?Although some electrical appliances seem to have similar principles, they are different in the selection of motors, such as electric fans and air conditioners. Most electric fans use single-phase motors. Single-phase motors have only one 220v live wire and one neutral wire, while air conditioners often uses the three-phase motor, which has three wires, 220v live wire, neutral wire, and 380v live wire. The most obvious difference between a single-phase motor and a three-phase motor is that the number of start capacitors is different. A single-phase motor is equipped with a start capacitor, while a three-phase motor has no start capacitor.6.2 Why Does a Three-phase Motor do not Need a Start Capacitor?Because the three-phase motor itself has three running windings and can generate a magnetic field by itself, the appearance of the magnetic field can effectively replace the start capacitor, so the three-phase motor is generally not equipped with a start capacitor. However, the start capacitor still plays an irreplaceable role in a single-phase motor, because there is only one running winding in a single-phase motor, which cannot form a rotating magnetic field, and the operation of electrical appliances can only rely on the start capacitor. In addition to the start capacitor in a single-phase motor, there is also a run capacitor. Although these two capacitors work together, the function of the start capacitor is much greater than that of the run capacitor, so once they start capacitor is damaged, the fan will make a lot of noise, The blade speed is reduced. If this happens to your electric fan, you might as well try to replace a start capacitor, the problem should be solved.6.3 The Relationship Between Start Capacitors and MotorAt present, in single-phase motors with low-power motors, the start capacitor is connected in series with the starting coil and then connected in parallel with the running coil to work at the same time. In order to speed up the start-up time of the high-power motor, a large capacitor to help start is added. After the motor is started, the additional large start capacitor is disconnected by the centrifugal switch. The smaller capacitor connected in series with the starting coil is responsible for the phase shift required during normal operation. Electric current, the power supply machine is operating normally. Is there a single-phase motor that is connected to the starting coil and connected in parallel with the running coil in the circuit from start to run and does not require other large capacitors to help start? Low-power motors are always used in the circuit. High-power motors have to add additional capacitors due to their large power and large starting distance.Figure11. Torque-speed characteristic6.4 What are the Functions of Start Capacitors, Run Capacitors, and Centrifugal Switches in Single-phase Motors?The start capacitor is used for phase separation, and the purpose is to make the current in the two windings produce a phase difference close to 90 ゜ to generate a rotating magnetic field, allowing the motor to run quickly in a static state. There is an automatic clutch switch in the motor. When the motor is started, the motor will continue to run due to inertia. When the speed reaches a certain speed, the start capacitor will be separated by centrifugal action and automatically connected to the run capacitor, and the motor will enter the normal working state. The function of the run capacitor is to keep the current in the two windings with a phase difference of 90° to generate a continuous rotating magnetic field. For motors with start capacitors, the rotational torque generated by the start capacitors is larger than that of the run capacitors, which is more suitable for starting with a load. Motors without start capacitors are not suitable for starting with a larger load.VII QuizThe starting capacitor of a single phase motor is(A) Electrolytic capacitor(B) Ceramic capacitor(C) Paper capacitor(D) None of the above.Answer: AⅧ FAQ1. What happens when a start capacitor goes bad?A motor connected to a run and start capacitor may still attempt to start if one or both of the capacitors has failed, and this will result in a motor that hums and will not remain running for long. ... In most cases of capacitor problems, such as damage or a loss of charge, the capacitor will need to be replaced. 2. What's the difference between a run capacitor and a start capacitor?The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current. A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor. 3. How do you test a start capacitor with an ohmmeter?To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity. 4. How to test a motor start capacitor?Motor run capacitor failure symptoms include warm air flowing from the vents inside the home, the air conditioner taking more time than usual to kick on or it turns off before it is programmed to, or there is a constant low hum emitting from the machine that isn't typical. 5. How do I test a capacitor with a multimeter?To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity. 6. How do you check if a capacitor is bad with a multimeter?If the capacitance value is within the measurement range, the multimeter will display the capacitor's value. It will display OL if a) the capacitance value is higher than the measurement range or b) the capacitor is faulty. 7. How do I test a capacitor without a multimeter?Just connect those two ends of the capacitor to a single-phase supply and switch it ON for a few seconds. Then take that two-terminal and short it, you will get a spark. 8. How can I check a capacitor?Put the Analog Multimeter in the Ohmmeter position and if there are multiple ranges, choose a higher range. Connect the leads of the capacitor to the multimeter probes and observe the readings on the multimeter. For a good capacitor, the resistance will be low in the beginning and will gradually increase. 9. Can I replace a start capacitor with a run capacitor?Start capacitors give a large capacitance value necessary for motor starting for a very short period of time (usually seconds long). A start capacitor can never be used as a run capacitor because it cannot handle current continuously. 10. Which is bigger, start or run capacitor?A lot of torque is necessary to start up an AC system, so a start capacitor will have greater capacitance than a run capacitor. 

I IntroductionA capacitor is an electronic component composed of an insulator between two conductors, like a sandwich. We can understand it as a container that holds the electric charge. In actual capacitors, two conductors are filled with an insulating dielectric. There are numerous types of dielectrics, so the types of capacitors formed are also different. For example, according to dielectric materials, capacitors can be divided into gas dielectric capacitors, liquid dielectric capacitors, inorganic solid dielectric capacitors, and organic solid dielectric capacitors; according to polarity, they can be divided into polarized capacitors and non-polarized capacitors. This article will introduce the various types of capacitors in detail and some additional basic knowledge of them, mainly explaining from the perspective of the manufacturing process and structure.Capacitors: types, use and testing. CatalogI IntroductionII The Basic Principle of CapacitorsIII Film Capacitor  3.1 Metal Foil Film Capacitor  3.2 Metallized Film CapacitorIV Electrolytic Capacitor  4.1 Aluminum Electrolytic Capacitors  4.2 Tantalum Electrolytic Capacitors  4.3 Niobium Electrolytic CapacitorsV Ceramic Capacitor  5.1 Ceramic Disc Capacitor  5.2 Multi-layer Ceramic Capacitor  5.3 Monolithic Capacitors  5.4 Classification of Ceramic MediaVI SupercapacitorVII Fixed, Trimmer and Variable Capacitors  7.1 Mica Capacitor  7.2 Paper Capacitor  7.3 Trimmer Capacitor  7.4 Variable CapacitorVIII Comparison of Polarized Capacitors and Non-polarized Capacitors  8.1 Medium  8.2 Performance  8.3 Capacity  8.4 Structure  8.5 Application Environments and UseIX Axial and Radial Leaded CapacitorsX A Quiz About Capacitor TypesⅪ FAQII The Basic Principle of CapacitorsCapacitors, along with inductors and resistors, are the three basic passive devices in electronics. The function of the capacitor is to store electrical energy in the form of electric field energy.Taking the parallel plate capacitor as an example, we briefly introduce the basic principle of capacitance.Figure1. Parallel Plate CapacitorAs shown in the figure above, a DC voltage is applied to two metal plates that are close to each other and are parallel to each other (the dielectric between the plates). After stabilization, the metal plate connected to the positive electrode of the voltage will exhibit a certain amount of positive charge, while the metal plate connected to the negative electrode of the voltage will exhibit an equal amount of negative charge. In this way, an electrostatic field is formed between the two metal plates, so the capacitor stores electrical energy in the form of electric field energy, and the stored charge is Q. The amount of charge stored in the capacitor Q is related to the voltage U and its own property (that is, the capacitance value C), that is, Q=U*C. According to the theoretical derivation, the capacitance formula of the parallel plate capacitor is as follows:In this formula:C is the capacitance value, the unit is F (Farad)ε is the dielectric constant of the medium, F/mS is the area of the metal flat plate, m²d is the distance between metal plates, mThe ideal capacitor contains a dielectric, and there is no free charge, so it is impossible to produce charge movement, which is the current.  How does the ideal capacitor pass AC power? AC PowerVoltage can form an electric field inside the capacitor, and alternating voltage will produce an alternating electric field. According to the law of full current in Maxwell's equations:This means that either a current or a changing electric field can generate a magnetic field. Maxwell defines ε(∂E/∂t) as a displacement current, which is an equivalent current and represents the change of the electric field. (The current here represents the current density, or J)Let the AC voltage change sinusoidally, ie:The actual displacement current is equal to the current density times the area:Therefore, the capacitive reactance of the capacitor is 1/ωC. When the frequency is high, the capacitive reactance will be very small, which means passing the high frequency. DC BlockingThe DC voltage does not change with time, the displacement current ε(∂E/∂t) is 0, and the DC component cannot pass through.The characteristics of actual capacitors are non-ideal and have some parasitic effects; therefore, a more complicated model is needed to represent the actual capacitors. The commonly used equivalent model is as follow:Figure2. Equivalent ModelSince the medium is not absolutely insulated, there is a certain conductivity; therefore, any capacitor has a leakage current, expressed by the equivalent resistance Rleak;The conductors and electrodes of the capacitor have a certain resistivity, and there is a certain dielectric loss of the dielectric; these losses are uniformly expressed as the equivalent series resistance ESR;There is a certain inductance in the conductor of the capacitor, which has a greater impact at high frequencies, expressed as the equivalent series inductance ESL;In addition, there is a certain hysteresis in any medium, that is, after the capacitor is quickly discharged, the voltage is suddenly disconnected, and the capacitor will recover part of the charge, which is represented by a series RC circuit（Related post: LC circuit）.Most of the time, the main concern is the ESR and ESL of the capacitor. Quality FactorAs with inductors, the quality factor of the capacitor can be defined, which is the Q value, which is the ratio of the stored power of the capacitor to the power loss:Qc=(1/ωC)/ESRThe Q value is a relatively important parameter for high-frequency capacitance. Self-Resonance FrequencyBecause of the existence of ESL, a resonant circuit is formed together with C, and its resonant frequency is the self-resonant frequency of the capacitor. Before the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases; after the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases, which is inductive. As shown in the following figure:Figure3. Self-Resonance FrequencyAccording to the capacitance formula, in addition to the size of the capacitor, the size of the capacitance is related to the Permittivity of the dielectric. The performance of the dielectric affects that of the capacitor, and different media are suitable for different manufacturing processes.Capacitors can be divided into three main categories according to the manufacturing process: Film Capacitor Electrolytic Capacitor Ceramic CapacitorIII Film CapacitorFilm capacitors are made by winding two plastic films with metal electrodes into a cylindrical shape, and finally encapsulated; because its medium is usually plastic material, also known as plastic film capacitors. Its internal structure is rough as shown in the following figure:Figure4. The Structure of Film CapacitorFilm capacitors can be divided into two categories according to the manufacturing process of their electrodes:3.1 Metal Foil Film Capacitor For metal foil film capacitors, a thin metal foil, usually aluminum foil, is directly added to the plastic film as an electrode. This process is relatively simple, the electrode is easy to lead out, and can be applied to large current occasions.3.2 Metallized Film CapacitorMetalized film capacitors form a thin metal surface directly on the surface of the plastic film by vacuum deposition process as an electrode. Because the thickness of the electrode is very thin, it can be wound into a capacitor with a larger capacity. However, due to the thickness of the electrode, it is only suitable for small current applications.Figure5. Metallized Film ConstructionThe metalized film capacitor has the function of self-repair, that is, if there is a breakdown point inside the capacitor, an avalanche effect will occur at the damaged place, and the vaporized metal will form a vaporized assembly surface at the damaged place, the short circuit disappears, and the damaged point is repaired. Therefore, the reliability of the metalized thin film capacitor is very high, and will not fail due to a short circuit. There are two winding methods for film capacitors:Inductive winding method Before winding, the lead has been connected with the internal electrode.After the non-inductive winding method, gold plating and other processes are used to connect the internal electrodes of the two end surfaces into one surface, so that a smaller ESL can be obtained, and the high frequency performance should be higher.In addition, there is a laminated type non-inductive capacitor, the structure is similar to MLCC, the performance is better, and it is easy to make SMD package.Figure6. Winding MethodsThe characteristic of the film capacitor is that it can achieve large capacity and high withstand voltage. However, due to process reasons, its size is difficult to be small, and it is usually used in strong electric circuits, such as the power electronics industry.Figure7. Winding MethodsIV Electrolytic CapacitorElectrolytic capacitors use metal as an anode, and form a metal oxide film on the surface as a medium, and then wet or solid electrolyte and metal as a cathode. Electrolytic capacitors are mostly polarized. If the metal on the cathode side also has an oxide film, it is a non-polarized electrolytic capacitor.Depending on the metal used, there are three types of electrolytic capacitors:4.1 Aluminum Electrolytic CapacitorsAluminum electrolytic capacitors should be the most widely used electrolytic capacitors and the cheapest. Its basic structure is shown in the following figure:Figure8. The Structure of Aluminum Electrolytic CapacitorThe manufacturing process of aluminum electrolytic capacitors is roughly as follows:First, the aluminum foil will form a very rough surface by electroetching process, which increases the surface area of the electrode and can increase the capacitance;The anode is oxidized by a chemical method to form an oxide layer as a medium;Then, a layer of electrolytic paper is added between the anode aluminum foil and the cathode aluminum foil as a separator, and is pressed and wound;Finally, fill the electrolyte, the electrolytic paper will absorb the electrolyte, and the package is molded.Wet aluminum electrolytic capacitors using electrolyte are the most widely used, with the advantages of large capacitance, high rated voltage, and low cost. The disadvantages are also obvious, that is, shorter life, poor temperature characteristics, and larger ESR and ESL. For hardware development, it is necessary to avoid over-design. In the case of meeting performance requirements, cheap is the biggest advantage.Recommendation: How to Test Aluminum Electrolytic Capacitors4.2 Tantalum Electrolytic CapacitorsThe most widely used tantalum electrolytic capacitor should use manganese dioxide as a solid electrolyte. The internal structure of the solid tantalum electrolytic capacitor is rough as shown in the figure below:Figure9. The Internal Structure of the Solid Tantalum Electrolytic CapacitorCompared with aluminum electrolytic capacitors, the dielectric constant of tantalum oxide (tantalum pentoxide) is much higher than that of aluminum oxide (aluminum oxide). With the same volume, the capacity of tantalum capacitors is larger than that of aluminum electrolytic capacitors. Tantalum capacitors have a longer life and more stable electrical performance.Figure10. The Internal Structure of the Solid Tantalum Electrolytic CapacitorTantalum capacitors also use conductive polymer as electrolyte, the structure is similar to the manganese dioxide tantalum capacitor in the above figure, which is to replace manganese dioxide with a conductive polymer. Conductive polymers have higher conductivity than manganese dioxide, so ESR will be lower. In addition, there are wet tantalum capacitors, which are characterized by super large capacity, high withstand voltage, and low DC leakage current, which is mainly used in military and aerospace fields.Figure11. Wet Tantalum Capacitors4.3 Niobium Electrolytic CapacitorsNiobium electrolytic capacitors are similar to tantalum electrolytic capacitors, in that niobium and its oxides replace tantalum. The dielectric constant of niobium oxide (niobium pentoxide) is higher than that of tantalum oxide (tantalum pentoxide). The performance of niobium capacitors is more stable and more reliable.V Ceramic CapacitorCeramic capacitors use ceramic materials as dielectric materials. There are many types of ceramic materials with different dielectric constants and stability, which are suitable for different occasions.Ceramic capacitors mainly include the following:5.1 Ceramic Disc CapacitorThe main advantage of the ceramic capacitor is that it can withstand high voltage, and it is usually used as a safety capacitor, which can withstand 250V AC voltage. Its appearance and structure are shown below:Figure12. The Structure of Ceramic Disc Capacitor5.2 Multi-layer Ceramic CapacitorMulti-layer ceramic capacitors, that is, MLCCs, chip multi-layer ceramic capacitors are currently the most widely used capacitor types in the world. Their standardized packaging and small size are suitable for automated high-density chip production.The internal structure of the multilayer ceramic capacitor is shown below:Figure13. Internal Structure of Chip Multilayer Ceramic Capacitor5.3 Monolithic CapacitorsBecause multilayer ceramics need to be sintered and porcelainized to form an integrated structure, the multilayer ceramic capacitors in lead packages are also called monolithic capacitors.The structure of monolithic capacitors is that several ceramic film blanks are covered with electrode paddle material, and after being laminated, they are wound into an inseparable whole at a time, and the outside is encapsulated with resin.Monolithic capacitors are a new type of capacitors with small volume, large capacity, high reliability and high-temperature resistance. Low-frequency monolithic capacitors with high dielectric constant also have stable performance and are actively small.5.4 Classification of Ceramic MediaAccording to EIA-198-1F-2002, ceramic media are mainly divided into four categories:Class I: Ceramic medium with temperature compensation characteristics, the dielectric constant is mostly low, not more than 200. It is usually a paraelectric medium. Under temperature, frequency and bias voltage, the dielectric constant is relatively stable and the change is small. The loss is also very low, the dissipation factor is less than 0.01.Figure14. Coding of Class 1 Capacitors According to EIA SpecificationThe most stable and most used is the C0G capacitor, or NP0. NP0 is the code name for the IEC/EN 60384-1 standard as Negative Positive Zero, using N and P for Positive and Negative deviations.Due to the low dielectric constant, the capacitance value of C0G capacitor is small and can be up to 0.1uF. The 0402 package usually has a maximum of 1000pF. Class II, III: Among them, the temperature characteristic A-S belongs to Class II, and the dielectric constant is about several thousand. The temperature characteristic T-V belongs to Class III, and the dielectric constant can be as high as 20000. It can be seen that the performance of Class III is more unstable. According to the classification of IEC, both Class II and III belong to the second category, high dielectric constant media. For example, X5R and X7R are Class II capacitors, which are widely used in power supply decoupling, while Y5V belongs to Class III capacitors, and their performance is not stable.Figure15. EIA Coding of Class 2 and 3 CapacitorsThe capacitance value of Class II and III capacitors can be up to several hundred uF, but due to the high dielectric constant medium, most of them are ferroelectric medium (Ferroelectric), and the temperature stability is poor. In addition, the dielectric constant of ferroelectric media will decrease under DC bias voltage. Class IV: The manufacturing process is different from the usual ceramic materials. The internal ceramic particles are all a thin oxide layer on the outside, and the core is a conductor. This type of capacitor has a large capacity but a small breakdown voltage. Due to the unstable performance and high loss of these capacitors, they have been basically eliminated.VI SupercapacitorSupercapacitor refers to a new type of energy storage device between a traditional capacitor and a rechargeable battery. There are two ways to store charge: EDLC and pseudocapacitance. It not only has the characteristics of rapid charge and discharge of the capacitor but also has the energy storage characteristics of the battery. The capacity of the supercapacitor is particularly large. It can replace the battery as a power supply device, and can also be used in conjunction with the battery. Supercapacitors charge fast, can be fully charged and discharged, and can be charged to any desired voltage, as long as the rated voltage is not exceeded. There are many applications of supercapacitors, for example, many cities in China have supercapacitor electric buses. There are also applications in some electronic products, such as some driving recorders, which can continue to supply power for several days.Figure16. SupercapacitorsVII Fixed, Trimmer and Variable CapacitorsA capacitor with a fixed capacitance is called a fixed capacitor. According to the different media can be divided into ceramics, mica, paper, film, electrolysis. Having described film capacitors, electrolytic capacitors, and ceramic capacitors, let's look at the other two types of fixed capacitors.  7.1 Mica CapacitorMica capacitors can be divided into foil type and silver type. Silver electroplating is very direct on mica sheets by vacuum evaporation or sintering method. Due to the elimination of the air gap, the temperature coefficient is greatly reduced and the capacitance stability is higher than foil type. Mica capacitors are widely used in high-frequency electrical appliances and can be used as standard capacitors. The glaze capacitor is made of a special mixture with a concentration suitable for spraying into a film. The medium is then sintered with a silver layer electrode to form a "monolithic" structure. Glass glaze capacitor is comparable to a mica capacitor in performance and can withstand various climates. It can generally work at 200℃ or higher, with rated working voltage up to 500 V and loss tan = 0.0005 ~ 0.008.Figure17. Silver Mica Capacitors7.2 Paper CapacitorPaper capacitors are widely used in radio and electronic equipment. Generally, two aluminum foils are used as electrodes, which are separated by overlapping winding of capacitor paper with a thickness of 0.008 ~ 0.012 mm. Simple manufacturing process, low price, can obtain a large capacitance, generally below 0.25 F, but the capacity error is large and difficult to control, good quality is ±10%, loss (tan ≤ 0.015), temperature and frequency characteristic stability is poor. The paper capacitors commonly used in the past are non-sealed, impregnated only with ground wax, paraffin wax and chlorinated diphenyl, etc., which are prone to aging and poor stability. They are easily affected by humidity, insulation resistance decreases after being affected by moisture, and atmospheric pressure also affects them. The paper capacitor whose core is sealed inside the metal or ceramic tube is of good quality and has little influence on the external climatic conditions. It can be normally used in the situation with the relative humidity up to 95 ~ 98 %. The electrode of metalized paper capacitor uses vacuum evaporation to directly attach the metal to the capacitor paper, which is only about 1/4 of the volume of the ordinary paper capacitor. Its main feature is its "self-recovery" function, that is, it can be "self-healing" after a breakdown. It is an improved type of paper capacitor. Oil-immersed capacitors have a higher voltage than ordinary paper capacitors, good stability, suitable for high-voltage circuits.Paper capacitors are intermediate frequency capacitors, which are generally used in low-frequency circuits and usually cannot be used in frequencies higher than 3 ~ 4 MHz.Figure18. Paper Capacitor7.3 Trimmer CapacitorTrimmer capacitors, also called semi-variable capacitors, have a capacitance that can be adjusted within a small range and fixed to a certain capacitance value after adjustment.Ceramic trimmer capacitors are of high quality and small size, and can usually be divided into two types: round tube type and round chip type.Trimmer capacitors for mica and polystyrene media are usually of spring-loaded structure, which is simple in structure but less stable.The wire-wound porcelain trimmer capacitor is used to change the capacitance by removing the copper wire (external electrode), so the capacitance can only be reduced and is not suitable for repeated debugging.7.4 Variable CapacitorAs the name implies, a variable capacitor means that the capacitance value can vary over a large range and can be determined to a certain value. Variable capacitors are divided into two forms: film medium and air medium. It is commonly used in coupling and tuning circuits, such as double capacitors, ceramic capacitors and so on.VIII Comparison of Polarized Capacitors and Non-polarized Capacitors8.1 MediumWhat is the medium? To put it bluntly, is the substance between the two plates of the capacitor. Most polarized capacitors use an electrolyte as the dielectric material. Generally, capacitors of the same volume have large polar capacitance. In addition, different electrolytic materials and processes produce polarized capacitors of the same volume. Furthermore, pressure resistance is also closely related to the use of dielectric materials. There are likewise many non-polarized capacitor dielectric materials, most of which use metal oxide film and polyester. Because the reversible or irreversible performance of the medium determines the use environment of polarized and non-polarized capacitors.8.2 PerformancePerformance is the requirement for use, and maximum demand is the requirement for use. If the metal oxide film capacitor is used for filtering in the power supply part of the TV, the capacitor capacity and withstand voltage required by the filtering must be achieved. Maybe only a power supply can be installed in this case. Therefore, only polarized capacitors can be utilized for filtering, and these capacitors are irreversible. In other words, the positive electrode must be connected to the high potential end, and the negative electrode must be connected to the low potential end. Generally, the electrolytic capacitor is above 1 microfarad for coupling, decoupling, power supply filtering, etc. Non-polarized capacitors are mostly below 1 microfarad, participating in resonance, coupling, frequency selection, current limiting, etc. Of course, there are also large-capacity and high-pressure-resistant ones, which are mostly used for reactive power compensation of electric power, phase shifting of motors, and frequency shifting power supply. There are many types of non-polarized capacitors, so this article won’t go into detail.Figure19. Classification of Capacitors8.3 CapacityAs mentioned earlier, the electrical media of the same volume are different, so the capacity is not equal.8.4 StructureIn principle, any shape capacitors can be used in the environment without considering the tip discharge. The electrolytic capacitors (polarized capacitors) that are usually used are round, and the square ones are rarely utilized. The shape of non-polarized capacitors varies. Like tube shape, deformed rectangle, sheet shape, square shape,combined square shape and round shape, etc., see where it is used. Of course, there are invisible. Intangible here refers to distributed capacitance. The distributed capacitance must not be ignored in high-neck and intermediate-frequency devices.8.5 Application Environments and UseIn the repair of home appliances, all of the above may be found. If you want to understand in a simple way, you have to find out by yourself.Because of the relationship between its internal materials and construction, the capacity of polarized capacitors (such as aluminum electrolysis) can be very large, but its high-frequency characteristics are not good, so it is suitable for power supply filtering and other occasions, but there are also good high-frequency characteristics. Polarized capacitor-tantalum electrolysis, its price is relatively high; Non-polarized capacitors are small in size, low in price, and satisfactory in high-frequency characteristics, but they are not suitable for large capacity. Like ceramic capacitors, monolithic capacitors, and polyethylene (CBB) capacitors, ceramic capacitors are generally used in high-frequency filtering and oscillation circuits.Figure20. Axial and Radial Type ConstructionIX Axial and Radial Leaded CapacitorsOne method of packaging capacitors is the lead structure. 　　Axial capacitance refers to the capacitance of the two pole leads on the same axis. Generally, it is a non-inductive structure. It is made of metalized polyester film as the dielectric/electrode. The wire is tinned copper clad steel wire (or flexible wire), the outer layer is wrapped with polyester tape, and both ends are sealed with epoxy resin.Figure21. Axial Lead StructureAxial leads (the leads are on the same plane as the capacitor axis) are radial leads. The figure below shows an example of a radial lead. The lead is in the radial position of the capacitor. Critical dimensions are lead spacing "S", height "H", length "L" and thickness "P'. Because they are inserted on the printed circuit board rather than on the surface of the circuit board like surface mount components, axial And radial elements are collectively referred to as "plug-in elements".Figure22. Radial Lead StructureX A Quiz About Capacitor TypesQuestion:The capacitors which use chemical reactions to store charge are calledA.ceramic capacitorsB.fixed capacitorsC.parallel plate capacitorsD.electrolytic capacitorsAnswer:D Ⅺ FAQ1. How do you identify a capacitor?Ceramic types of capacitors generally have a 3-digit code printed onto their body to identify their capacitance value in pico-farads. Generally, the first two digits indicate the value of the capacitor and the third digit indicates the number of zero's to be added. 2. What are the 2 types of capacitors?Capacitors are divided into two mechanical groups: Fixed capacitors with fixed capacitance values and variable capacitors with variable (trimmer) or adjustable (tunable) capacitance values. The most important group is the fixed capacitors. Many got their names from the dielectric. 3. Can a 440v capacitor be used for a 230v application?The 440 volts listed on the cap is the maximum allowable voltage the capacitor can handle. You could actually use a 370-volt cap on 230 volts. ... Capacitor is connected in series with the auxiliary winding of the motor. Since winding is inductive, the voltage across the capacitor is much higher than the supply voltage. 4. What side of the capacitor is positive?Electrolytic capacitors have positive and negative sides. To tell which side is which, look for a large stripe or a minus sign (or both) on one side of the capacitor. The lead closest to that stripe or minus sign is the negative lead, and the other lead (which is unlabeled) is the positive lead. 5. What does 50 uF mean on a capacitor?It's a symbol that means micro so 50 μF means 50 microfarads or 000050 Farads. The farad is such a large unit that the microfarad is the practical unit for capacitance. 6. What are capacitors in parallel called?When capacitors are connected in parallel, the total capacitance is the sum of the individual capacitors' capacitances. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors. 7. Are AC and DC capacitors interchangeable?You can use AC caps on DC. AC caps have a much higher DC rating. All capacitors have microscopic air bubbles between the foil layers. DC is just a special case where the polarity of the voltage does not change, so you can use AC capacitors - as is - in a DC application. 8. Which type of capacitor is polarized?The only type of capacitor that is polarized (works differently depending on which way the current is flowing) is the electrolytic capacitor. Electrolytic capacitors have higher capacitance, but for most purposes, the non-polarized capacitor is preferred. 9. What is the main function of the capacitor?A capacitor is an electronic component that stores and releases electricity in a circuit. It also passes alternating current without passing direct current. A capacitor is an indispensable part of electronic equipment and is thus almost invariably used in an electronic circuit. 10. What happens if you use the wrong size capacitor?If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat. 

I IntroductionTwo adjacent conductors are sandwiched by a layer of a non-conductive insulating medium to form a capacitor. Capacitors are one of the most commonly used electronic components. They play an important role in circuits like tuning, bypassing, coupling, and filtering. For example, they are often used in the tuning circuit of the transistor radio, coupling circuit and bypass circuit of the color TV. This article mainly introduces how to properly use multimeters to test capacitors and aluminum electrolytic capacitors (solid state capacitor), including detailed operating steps, working principles, notice, and explaining some fundamental knowledge about capacitors. We also have a related post about how to check start capacitors you may be interested in. Don't miss it! How to Test Capacitors with a Digital MultimeterCatalogI IntroductionII Definition of CapacitorIII The Reasons and Effects of Testing Capacitors and Withstand Voltage Performance  3.1 Why Should We Measure the Capacitance of A Capacitor?  3.2 Why Should Capacitors Undergo A Withstand Voltage Test?IV The Difference of Capacitors with Different Capacity in Test  4.1 Small-capacity Capacitor Test  4.2 Large-capacity Capacitor Test  4.3 Supercapacitor TestV How to Test Capacitors with A Multimeter?  5.1 Direct Test with A Capacitor  5.2 Test with Resistance File  5.3 Test with Voltage File  5.4 Test with Buzzer  5.5 Use a Digital Multimeter to Measure Capacitance Greater Than 20μFVI How to Detect Capacitors in Aluminum Capacitors  6.1 Appearance Physical Inspection  6.2 Capacity and Loss Test  6.3 Ripple Voltage Test  6.4 Leakage Current Test  6.5 Explosion Test  6.6 Temperature TestVII Considerations for Capacitor TestingVIII One Question Related to Testing Capacitor  8.1 Question  8.2 AnswerⅨ Frequently Asked Questions about How to Test a CapacitorII Definition of CapacitorCapacitors comprise components that store electricity and electrical energy (potential energy). A conductor is surrounded by another conductor, or the electric field lines emitted by one conductor all terminate in the conduction system of the other conductor, called a capacitor. This is a short introduction of capacitor. Under what circumstances do you need to test the capacitors, that's when you have capacitor uncertainty in use. So let's analyze it here. III The Reasons and Effects of Testing Capacitors and Withstand Voltage Performance3.1 Why Should We Measure the Capacitance of A Capacitor?The purpose of measuring the capacitance value of a capacitor in a general sense of electricity is to check the change of its capacitance value. By comparing the measured value with the value on the nameplate, you can judge whether the internal wiring is correct and whether the insulation has deteriorated because of moisture, whether the component has broken down, and whether oil leakage has caused the capacitance to decrease. So be careful during the substantial operation. 3.2 Why Should Capacitors Undergo A Withstand Voltage Test?The withstand voltage test refers to the test of the capability of withstanding voltage of various electrical devices and structures. The process of applying a high voltage to an insulating material or an insulating structure without damaging the performance of the insulating material is considered a withstand voltage test. Broadly speaking, the primary purpose of the capability of withstanding voltage test is to check the ability of the insulation to withstand working voltage or overvoltage, and then to check whether the insulation performance of the product equipment meets safety standards capability of withstanding voltage test is to check the ability of the insulation to withstand working voltage or overvoltage, and then to check whether the insulation performance of the product equipment meets safety standards.Figure1. Capacitor TestingIV The Difference of Capacitors with Different Capacity in Test4.1 Small-capacity Capacitor TestThe capacitance of a small-capacity capacitor is generally below 1 UF because the capacity is too minor, the charging phenomenon is unobvious, and the angle of the hand to the right is not large when measuring. Therefore, it is generally impossible to estimate its capacitance with a multimeter, but only to detect whether it has leakage or breakdown. Under normal conditions, the resistance value of both ends of the multimeter R × 10 k should be infinite. If the certain resistance value is measured or the resistance value is close to 0, it means that the capacitor has leaked electricity or has been damaged by a breakdown.Related recommendation: How to Test Ceramic Disc Capacitor 4.2 Large-capacity Capacitor TestLarge capacity can generally be tested by 1K-10K, see the sweep of the meter during charging, and the resistance value indicated by the last meter. The closer to the left, the better. If the resistance is too small, it cannot be used. 4.3 Supercapacitor TestThe method of measuring supercapacitors is completely different from other types of capacitors. Supercapacitors have exceptionally large capacitance values that cannot be measured directly by standard equipment. Ordinary methods for testing the capacitance of these capacitors are by charging the supercapacitors at the rated voltage and discharging the supercapacitors by a constant current load.Figure2. Different CapacitorsV How to Test Capacitors with A Multimeter?5.1 Direct Test with A CapacitorSome digital multimeters have the function of measuring capacitance, and their ranges are divided into five ranges of 2,000p, 20n, 200n, 2μ and 20μ. When measuring, you can directly insert the two pins of the discharged capacitor into the Cx jack on the meter board and select the appropriate range to read the display data. 2,000p file, suitable for measuring capacitance less than 2000pF; 20n file, suitable for measuring the capacitance between 2000pF and 20nF; 200n file, suitable for measuring the capacitance between 20nF and 200nF; 2μ file, suitable for measuring between 200nF and 2μF Capacitance; 20μ range, suitable for measuring the capacitance between 2μF and 20μF. Experience has shown that some types of digital multimeters (like DT890B +) allow a considerable error when measuring small-capacity capacitors below 50pF, and there is almost no reference value for measuring capacitance below 20pF. At this time, the small value capacitance can be measured by the series method. Method: First find a capacitor of about 220pF, use a digital multimeter to measure its actual capacity C1, and then connect the small capacitor to be tested in parallel to measure its total capacity C2. The difference between the two (C1-C2) is subsequently the capacity of small capacitors under test.It is extremely accurate to measure the small capacitance of 1 ~ 20pF with this method.Figure3. How to Test a Capacitor with a Multimeter5.2 Test with Resistance FileThe practice has proved the charging process of capacitors can also be observed by using a digital multimeter, which actually reflects the change of charging voltage in discrete digital quantities. Assuming that the digital multimeter's measurement rate is n times/second, in the process of observing the charging of the capacitor, you can see n readings that are independent of each other and increase sequentially. According to this display characteristic of the digital multimeter, it is possible to detect the quality of the capacitor and estimate the size of the capacitance. The following describes the method of detecting the capacitor using the resistance meter of a digital multimeter, which is of practical value for instruments without a capacitor. This method is suitable for measuring large-capacitance capacitors from 0.1 μF to several thousand microfarads. 5.2.1 Operation Method of MeasurementAs shown in Figure 4, set the digital multimeter to the appropriate resistance level. The red and black test leads respectively to touch the two poles of the capacitor Cx under test. At this time, the displayed value will gradually increase from "000" until the display Overflow symbol "1."If"000" is consistently displayed, it means the capacitor is short-circuited internally; if it is constantly displayed, the internal poles of the capacitor may be open-circuited, or the selected resistance level may be inappropriate. When checking electrolytic capacitors, pay attention to the red test lead (positive charge) is connected to the positive electrode of the capacitor, and the black test lead is connected to the negative electrode of the capacitor.Figure4. Digital Multimeter 5.2.2 Measurement PrincipleFigure5 shows the measurement principle of measuring capacitors with resistance files. During the measurement, the positive power source charges, the capacitor Cx to be measured through the standard resistor R0. At the moment when charging starts, Vc = 0, so “000” is displayed. As Vc gradually increases, the displayed value increases. When Vc = 2VR, the meter starts to display the overflow symbol "1." The charging time t is the time required for the displayed value to alter from "000" to overflow. This time interval can be measured with a quartz meter.Figure5. Principle of Measurement 5.2.3 Measured Data Using DT830 Digital Multimeter to Estimate CapacitanceThe principle of selecting the resistance range is: when the capacitance is small, a high resistance should be selected, and when the capacitance is large, a low resistance should be selected. If you use a high-resistance range to estimate a large-capacity capacitor, the measurement time will last a long time because the charging process is very slow. If you use a low-resistance range to check a small-capacity capacitor, the meter will always show an overflow because the charging time is extremely short, and you cannot see the change. 5.3 Test with Voltage FileDetecting capacitors with the DC multimeter of a digital multimeter is actually an indirect measurement method. This method can measure small-capacitance capacitors from 220pF to 1μF, and can accurately measure the capacitor leakage current.5.3.1 Measurement Methods and PrinciplesThe measurement circuit is shown in Figure6. E is an external 1.5V dry battery. Set the digital multimeter to the DC 2V range, connect the red test lead to one electrode of the capacitor Cx under test, and the black test lead to the battery negative. The input resistance of the 2V range is RIN = 10MΩ. After the power is turned on, battery E charges Cx via RIN and starts to establish voltage Vc. The relationship between Vc and charging time t isFigure6. Wiring Diagram of Measuring Capacitor with Voltage Block Here, because the voltage across RIN is the instrument input voltage VIN, so RIN actually has the function of a sampling resistor. obviously,VIN (t) = E-Vc (t) = Eexp (-t / RINCx) (5-2)Figure7 is the change curve of the input voltage VIN (t) and the charging voltage Vc (t) on the capacitor under test. It can be seen from the figure that the change process of VIN (t) and Vc (t) is just the opposite. The curve of VIN (t) decreases with time, while Vc (t) increases with time. Although the meter shows the change process of VIN- (t), it indirectly reflects the charging process of the capacitor Cx under test. During the test, if Cx is open (no capacity), the displayed value will always be “000”. If Cx is internally short-circuited, the displayed value will always be the battery voltage E and will not change with time.Figure7. Change Curve of VIN (t) and Vc (t) Equation (5-2) shows that when the circuit is turned on, t = 0, VIN = E, the initial display value of the digital multimeter is the battery voltage, and then as Vc (t) increases, VIN (t) gradually decreases. Until VIN = 0V, the Cx charging process ends, at this timeVcx (t) = EUsing digital multimeter voltage level detection capacitor, not only can check small-capacitance capacitors from 220pF to 1μF, but also measure the capacitor leakage current. Let the leakage current of the capacitor being measured be ID, and the stable value displayed by the meter at the end is VD (the unit is V), thenFigure8. Equation (5-3) 5.3.2 ExamplesExample 1:The measured capacitance is a 1μF / 160V fixed capacitor, using the 2VDC range of the DT830 digital multimeter (RIN = 10MΩ). Connect the circuit according to Figure6. Initially, the meter displayed 1.543V, and then the displayed value gradually decreased. After about 2 minutes, the displayed value stabilized at 0.003V. Find the leakage current of the capacitor under test.Figure9. Equation The leakage current of the capacitor under test is only 0.3nA, indicating good quality.Example 2:The capacitor under test is a 0.022μF / 63V polyester capacitor. The measurement method is the same as in Example 1. Due to the small capacity of this capacitor, VIN (t) decreases rapidly during measurement, and after about 3 seconds, the displayed value decreases to 0.002V. Substituting this value into equation (5-3), the leakage current was calculated to be 0.2nA. 5.3.3 Notes(1) Before measurement, the two pins of the capacitor should be short-circuited and discharged, otherwise, the change process of the reading may not be observed.(2) Do not touch the capacitor electrode with both hands during the measurement to avoid meter jumping.(3) During the measurement, the value of VIN (t) changes exponentially, and decreases rapidly at the beginning. With the increase of time, the decline rate will become slower and slower. When the capacitance of the capacitor Cx under test is less than a few thousand picofarads, because VIN (t) initially drops too quickly, and the meter's measurement rate is too low to reflect the original voltage value, the initial display value of the meter is lower than the battery Voltage E.(4) When the measured capacitor Cx is greater than 1 μF, in order to shorten the measurement time, a resistance file can be used for measurement. However, when the capacitance of the capacitor under test is less than 200pF, it is difficult to observe the charging process because the change in the reading is very short. 5.4 Test with BuzzerUsing the buzzer file of the digital multimeter, you can quickly check the quality of the electrolytic capacitor. The measurement method is shown in Figure10. Set the digital multimeter to the buzzer position, and use two test leads to contact the two pins of the capacitor Cx under test. A short beep sound should be heard, the sound will stop, and the overflow symbol "1" will be displayed. Then, measure the two test leads again, and the buzzer should sound again, and the overflow symbol “1” will be displayed at last, which indicates that the electrolytic capacitor under test is basically normal. At this time, you can dial to 20MΩ or 200MΩ high resistance to measure the leakage resistance of the capacitor to determine its quality.Figure10. Wiring Diagram For Testing Electrolytic Capacitor with Buzzer The principle of the above measurement process is: At the beginning of the test, the charging current of the instrument to Cx is large, which is equivalent to the path, so the buzzer sounds. As the voltage across the capacitor continues to increase, the charging current rapidly decreases, and finally, the buzzer stops sounding. During the test, if the buzzer keeps sounding, it means that the internal of the electrolytic capacitor has been short-circuited. If the buzzer keeps sounding and the meter always shows "1" when the meter pen is repeatedly measured, it means that the capacitor under test is open or the capacity disappears. 5.5 Use a Digital Multimeter to Measure Capacitance Greater Than 20μFFor common digital multimeters, the maximum measurement value of the capacitance file is 20 μF, which sometimes cannot meet the measurement requirements. For this reason, the following simple method can be used to measure the capacitance of more than 20μF with the capacitance file of the digital multimeter, and the maximum capacitance of several thousand microfarads can be measured. When using this method to measure large-capacitance capacitors, there is no need to make any changes to the original digital multimeter circuit. The measurement principle of this method is based on the formula C string = C1C2 / (C1 + C2) of two capacitors in series. Since two capacitors with different capacities are connected in series, the total capacity after the series connection is smaller than that of the capacitor with the smaller capacity. Therefore, if the capacity of the capacitor to be measured exceeds 20 μF, only one capacitor with a capacity of less than 20 μF is used. In series with it, you can measure directly on the digital multimeter. According to the formula of two capacitors in series, it is easy to derive C1 = C2C string / (C2-C string). Using this formula, the capacitance value of the measured capacitor can be calculated. Here is a test example to illustrate the specific method of using this formula. The component under test is an electrolytic capacitor with a nominal capacity of 220 μF, and is set to C1. Select an electrolytic capacitor with a nominal value of 10μF as C2, use a digital multimeter 20μF capacitor to measure the actual value of this capacitor as 9.5μF, and connect the two capacitors in series to measure the C string as 9.09μF. Substituting C2 = 9.5 μF and C string = 9.09 μF into the formula, thenC1 = C2C string / (C2-C string) = 9.5 9.09 / (9.5-9.09) ≈211 (μF)Figure11. Digital MultimeterNote: No matter how much the capacity of C2 is selected, a capacitor with a larger capacity must be selected under the premise of less than 20μF, and C2 in the formula should be substituted into the actual measured value instead of the nominal value, which can reduce errors. The two capacitors are connected in series and measured with a digital multimeter. Due to the capacitance error and measurement error of the capacitor itself, as long as the actual measured value is close to the calculated value, the capacitor C1 to be measured is considered good. capacity. In theory, this method can measure the capacitance of any capacity, but if the capacity of the capacitor under test is too large, the error will increase. The error is proportional to the size of the capacitor to be measured.Do you want to know about other tools to test capacitors? You can Three Measuring Tools to Test Capacitors. VI How to Test Aluminum Electrolytic Capacitors6.1 Appearance Physical Inspection(1) First check whether the capacitor under test has a formal "Product Specification", which includes the product name, specifications, installation dimensions, process requirements, technical parameters, and supplier name, address and contact information to ensure this. Batch products are provided by regular manufacturers. The logo on the capacitor should include the trademark, working voltage, standard capacitance, polarity, and operating temperature range. (2) Refer to the process parameters in the “Product Specification” and observe whether the appearance, color, and material of the capacitor are consistent with the process indicators marked on it. (3) Use a vernier caliper to confirm the installation size of the capacitor to ensure that the diameter, height, and diameter and spacing of the lead-out terminal are within the tolerance of the product process, and the external dimensions must meet the company's selection requirements. (4) Check the appearance of the capacitor to ensure its appearance is neat, without obvious deformation, breakage, cracks, spots, dirt, rust, etc., and its marking is clear, firm, correct and complete. (5) Check the lead-out terminals to ensure that their terminals are straight, free from oxidation, rust, and have no effect on their conductive properties and that the lead-out terminals are free of distortion, deformation, and mechanical damage that affects insertion and removal. (6) Check that the production date marked on the electrolytic capacitor should not exceed six months, and make a record.Figure12. Aluminum Electrolytic Capacitor6.2 Capacity and Loss Test(1) Use the electric bridge to test whether the actual capacity is consistent with the nominal capacity (the electrolytic capacitor generally has an error range of ± 20%). The loss tangent value tanθ (that is, the D value) is in compliance with the standard. (2) How to use the Zen tech bridge tester: After connecting the power supply correctly, press the "POWER" key to turn on the tester's working voltage; press the "LCR" key to select the test type (L: Inductance, C: Capacitance, R: resistance). (3) Press the "UP" and "DOWN" keys to select the test range (μF, nF, pF) and press the "FREQ" key to select the test frequency (100HZ,(120HZ, 1KHZ) can choose the required test frequency according to the technical parameters provided by the manufacturer, the test in this article selects "100HZ". (4) Press "SERIES" (parallel) and "PARALLEL" (parallel) to select the connection mode for the test, small capacitance (less than 10μF)To use parallel mode, use large mode (10μF and above) in series mode. (5) After the setting is completed, connect the bridge test ports ("LOW" and "HIGH") to the two ends of the capacitor, and use the label paper to record the capacity value and loss value on the display respectively. And attach the label paper to the corresponding capacitor for subsequent analysis. 6.3 Ripple Voltage Test(1) Connect the circuit as shown below, and connect the capacitor to be tested to the adjustable DC power supply (note that the positive and negative poles are not connected reversely). Connect the positive electrode of the oscilloscope probe with a non-inductive capacitor (1μF 1200V.DC) in series to the positive electrode of the capacitor to be tested.Figure13. Circuit of Ripple Voltage Test (2) For the setting of the oscilloscope, it must be set to the DC test position first, and the fine adjustment knob of the oscilloscope voltage must be locked. (3) During the test, the DC voltage should be slowly increased to the rated voltage with a voltage regulator, and the changes displayed by the oscilloscope should be closely monitored. The correct range should be selected to ensure that the voltage can be accurately read from the oscilloscope waveform. (4) Take the ripple waveform with the camera, and record the range and division of the oscilloscope with label paper (that is, calculate the ripple voltage and paste it on the corresponding capacitor for subsequent analysis and comparison. (5) After the recording is completed, disconnect the DC power supply, discharge the capacitor under test and the non-inductive capacitor with the bulb load, and then remove the capacitor under test from the test bench. 6.4 Leakage Current Test6.4.1 Indirect Measurement Method OneConnect as shown below. Connect a 1K resistor in series with the capacitor under test and connect it to a DC adjustable power supply. Use an oscilloscope probe to connect to both ends of the resistor. Indirectly calculate the leakage current of the capacitor to be measured by sampling the voltage signal across the resistor. Operating essentials and precautions: After the circuit is connected, adjust the DC adjustable power supply to the rated voltage of the capacitor. After the circuit is equilibrated for two minutes, read the voltage value across the resistor. When reading the oscilloscope, the voltage trimming knob should be locked. Record the maximum value of the voltage waveform as the voltage value and divide it by the resistance value to obtain the value of the leakage current. The current is too large and the resistor is burned out. After the test, the capacitor should be discharged and then removed to avoid accidents.Figure14. Circuit 6.4.2 Indirect Measurement Method TwoConnect the wiring as shown in the figure, and add an air switch in series between the capacitor and the DC power supply. First close S1 and S2 respectively, and adjust the voltage regulator to the rated voltage to charge the capacitor for two minutes.Figure15. Circuit After that, both S1 and S2 are disconnected. At this time, the adjustable power supply is at the rated value. Do not move. Add a milliamp meter between S1 and S2, as shown in the figure below: S1 and S2 are both closed, and the leakage current can be directly read through the milliamp meter after one minute of stabilization.Figure16. Circuit 6.4.3 PrecautionsRemember not to connect the milliamp meter to the line directly when the capacitor is not charged, because the initial charging current is large, the milliamp meter will be burned out by accident. In the disassembly process, first discharge the capacitor with the bulb load. When discharging, remove the milliamp meter first, and ensure that the discharge current does not pass the test resistor to prevent damage to the test resistor and the millimeter meter.6.4.4 Leakage Current at 1.2UnAdjust the DC voltage to 1.2 times the rated voltage of the electrolytic capacitor, measure its leakage current again and compare different samples. 6.5 Explosion Test6.5.1 DC TestApply reverse DC voltage to the capacitor under test, slowly adjust the adjustable DC voltage, and observe the current closely with a clamp meter.The DC power setting is generally not more than 30V. The current value is set according to the size of the capacitor as follows:When the capacitor diameter is 6mm ≤ 22.4mm, the current cannot exceed 1A; when the capacitor diameter is> 22.4mm, the current cannot exceed 10A. 6.5.2 Observe The Surface Temperature of The CapacitorDuring the experiment, use a thermometer to closely observe the surface temperature of the capacitor (the sensing contact of the thermometer can be wrapped around the capacitor with tape). Note that the initial current is very small and almost zero. When the temperature of the capacitor rises (about 35-40 ° C) The current is significantly increased. At this time, close observation should be made. When the current reaches or approaches 10A, the voltage should be lowered to ensure that the current is controlled within 10A. 6.5.3 Capacitor Safety ValveWithin 30 minutes after the start of the test, the capacitor safety valve should be opened. If the capacitor fuse is open, the power should be cut off immediately (the electrolytic capacitor of 350V 6800F will automatically open under the following conditions, the current is about 8A, the surface temperature is about 45-60 ° C.), If the current is close to 10A and the fuse is still 30 minutes later, If it is not turned on, this function is missing.Figure17. DC Digital Voltmeter6.6 Temperature TestThe capacity of a capacitor will change due to different ambient temperatures. In general, the capacity will increase as the temperature rises. The temperature test is to test the change of capacitance after equilibration under the set temperature. 6.6.1 High-Temperature Test(1) Connect two small wires to the lead-out terminal of the capacitor to be tested respectively, and test the capacity of the two lead terminals at normal temperature, and label them for record.(2) Put the capacitor into the high and low temperature alternating humidity and heat test box, and leave the leads outside the test box to test the capacitance.(3) Turn on the test box switch button, click "Temperature Setting" on the screen, set the temperature to 100 ° C, and click "Run" to start the test box.(4) Test the capacity again about 2 hours after the temperature reaches 100 ° C, and calculate the percentage change in capacity (the initial measurement of the difference). 6.6.2 Low-Temperature Test(1) Put the capacitor to be tested into the test box (be careful not to use capacitors that have been tested at high temperatures, except for special needs).(2) Turn on the test box switch button, click "temperature setting" on the screen, set the temperature to -25 ° C, and click "run".(3) Test the capacity again about 2 hours after the temperature reaches -25 ° C, and calculate the percentage change in capacity (the initial measurement of the difference). 6.6.3 PrecautionsThe test should pay close attention to whether there is any obvious change in the capacitor. If serious conditions such as cracking of the capacitor surface and opening of the safety valve occur, the test box should be stopped immediately. During the test, the operating procedures of the test box should be strictly followed, and the door of the test box should not be opened at will. At the end of the high temperature test, the capacitor can only be taken out after the temperature inside the test box has dropped to prevent accidents such as burns.Figure18. CapacitorsVII Considerations for Capacitor Testing(1) When measuring with a multimeter, select the gear according to the rated voltage of the capacitor. For example, the capacitor voltage commonly used in electronic equipment is low, only a few volts to dozens of volts. If the multimeter RX10k is used for measurement, the battery voltage in the meter is 12 ～ 22.5V, which is likely to cause capacitor breakdown. Therefore, the RXlk file should be used. measuring.(2) For the capacitor just removed from the line, be sure to discharge the capacitor before measurement to prevent the residual charge in the capacitor from being discharged to the meter and damage the meter.(3) For capacitors with high working voltage and large capacity, the capacitors should be sufficiently discharged, and the operator should have protective measures to prevent electric shocks during discharge. VIII One Question Related to Testing Capacitor8.1 QuestionWhat should we do when checking a capacitor with an ohm meter？8.2 AnswerTo remove the capacitor from the circuit. It's usually easy to remove a start or run capacitor – you simply unhook it from its harness and disconnect the wires. However, be careful to avoid touching the capacitor terminals. If the capacitor isn't dead, it might have a full charge, and if so, you could get a serious shock.  Ⅸ Frequently Asked Questions about How to Test a Capacitor1. How do you check if a capacitor is bad with a multimeter?Use the multimeter and read the voltage on the capacitor leads. The voltage should read near 9 volts. The voltage will discharge rapidly to 0V because the capacitor is discharging through the multimeter. If the capacitor will not retain that voltage, it is defective and should be replaced. 2. How do you test a capacitor at home?Set your voltmeter to read DC voltage (if it's capable of reading both AC and DC). Connect the voltmeter leads to the capacitor. Connect the positive(red) lead to the positive (longer) terminal and the negative (black) lead to the negative (shorter) terminal. Note the initial voltage reading. 3. How to test capacitor using multimeter? 4. Can you test capacitor on board?You just cannot test a bad capacitor inside or outside a circuit board by measuring its capacitance value with a capacitor meter or a multimeter. ... When the capacitor is outside the board, sometimes a bad capacitor may give you a proper capacitance value on the multimeter or capacitor meter. 5. What is the best capacitor tester?Best Capacitance Meter Review:Signstek MESR-100 V2 Auto Ranging in Circuit ESR LCR Meter CapacitorELIKE Digital Capacitor Tester 0.1pF to 20mFHoneytek A6013l Capacitor TesterMESR-100 circuit tester, KKMOON mesr-100 capacitor testerMultimeter Digital Capacitance Meter Capacitor Tester 0.1Pf to 2000uFExcelvan M6013 Digital Auto Ranging Capacitance Meter Capacitor TesterDigital Capacitance Meter Professional Capacitor 0.1Pf – 20000Uf 6. How do you test a capacitor with a cheap multimeter? 7. How many ohms should a capacitor have?1,000 ohmsSet it to its highest ohm (Ω) setting, at least 1 kΩ (1,000 ohms). At this setting, the meter generates a small current when you connect the meter leads to the capacitor terminals. 8. What is the capacitor symbol on a multimeter?Most digital multimeters use a symbol similar to –|(– to signify capacitance. Move the dial to that symbol. If several symbols share that spot on the dial, you may need to press a button to cycle between them until the capacitance symbol appears on the screen. 9. What if a capacitor reads high?It is reading as if there is a short circuit across it. If we read a very high resistance across the capacitor (several MΩ), this is a sign that the capacitor likely is defective as well. It is reading as if there is an open circuit across the capacitor. ... But not 0Ω or several MΩ. 10. What is the first step in testing a capacitor?The first and most simple is to inspect the capacitor. If it appears “blotted” or swelled, it is a safe bet that it is bad. It is good practice to go ahead and perform the following test even though it is swelled. Make a sketch of the wires connected to the capacitor and note the colors or numbers that identify them.

Ⅰ IntroductionAn operational amplifier, or op-amp for short, is fundamentally a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. Learn more about the most common opamp basics, essential knowledge when selecting and using an op amp in electronics. We can conclude our section and look at Op Amp basics with the following properties and questions. Opamp Basics: Op-Amp CircuitsCatalogⅠ IntroductionⅡ Amplifier Figures of MeritⅢ Q & AⅣ Application: LM358 Classic CircuitsⅡ Amplifier Figures of MeritNegative FeedbackIt is a important technique to improve bandwidth and distortion and control gain.Open-loop GainIt refers to the ratio of the voltage change at the output of the amplifier to the voltage change at the input when the amplifier input and output are open. Common-mode Rejection Ratio (dB)It is the ratio of the amplifier's amplification factor of the differential voltage signal to the amplification factor of the common mode voltage signal.Input Current NoiseIt is the equivalent current noise applied in parallel with the input of the noiseless amplifier.Output CurrentIt refers to the current driven by the load at the output of the op amp. It is usually a function: input overdrive, correlation between output voltage and power supply, temperature, source, and drain characteristics will differ.Phase MarginIt is the phase shift between an output of the same frequency and an inverting input in an open-loop circuit.Voltage GainIt is the ratio of the change in output voltage to the change in input voltage.Programmable Gain BufferIt can set the gain resistance of the op amp (integrated on the template), and the gain can be set to +1, +2, or -1 through simple external connections.Saturation VoltageIt is the voltage between the collector and emitter of the transistor under saturation conditions. In the saturated state, the emitter-base and collector-base are forward biased, so that the voltage between the collector-emitter is very low.Rise TimeThis refers to the time required for the output voltage to change from 10% of its final value to 90% of its final value.Unity-gain BandwidthIt refers to the frequency at which the amplifier's open-loop gain is equal to one. If the op amp frequency response has a single-pole roll-off, the unity-gain bandwidth is equal to 1UGBW.Strobe “OFF” VoltageThe strobe “OFF” voltage is the minimum voltage at the strobe pulse and is guaranteed not to interfere with the comparator operation.Input Current IndexIt refers to the average of the current drawn from the two input pins. In addition, the input current is also commonly called bias current.Gain Bandwidth ProductIt refers to the product of the amplifier's bandwidth and the gain at which the bandwidth is measured.Large Signal Voltage GainIt refers to the ratio of the change in output voltage to the change in input voltage. This parameter is usually specified at a large output voltage, smaller than the maximum output voltage, which is the typical value under direct current conditions.Offset Voltage Temperature CoefficientIt refers to the average rate of change in offset voltage due to changes in junction temperature within a specified temperature range.Output High VoltageIt refers to the high DC output voltage of the comparator, which produces the high output current. And it is usually related to the totem pole or push-pull output of the comparator.Input Source CurrentIt refers to the maximum output positive current produced under the comparator's push-pull output state.Total Harmonic Distortion (THD)When a pure sinusoidal signal is input to the op amp as Vin (w) = Vpsin (wt):Input harmonic distortion: Vout(w)a1Vpsin(wt)+a2Vpsin(wt)+...+anVpsin(nwt)The expression of THD is: THD(%)=[sqrt(a2xa2+a3xa3+...+anxan)/a1]x100Common-Mode Input Impedance (RINCM)It refers to the ratio of the change in the common-mode input voltage to the change in the input current at the inverting or non-inverting terminal.Output Low VoltageIt refers to a low DC output voltage. The output drive is a low voltage sink current. This specification is usually related to the totem pole or push-pull output of the comparator.Using a CMOS op amp as the output driver, although the circuit works well, but requiring a 1m shielded cable, and the oscillation of the operational amplifier is about 1MHz when there is no input signal. If shorten the cable to 10cm, the oscillation is stable.Some op amps are not suitable for driving capacitive loads directly, such as long shielded cables, which is a capacitive load. In addition, coaxial cables have about 60-100pF capacitance per meter.Harmonic DistortionIt refers to the unwanted spurious signals generated at the amplifier output due to the non-linearity of the signal line. When the input is a sinusoidal signal, these spurious signals will appear as integer times of the input frequency (for example, second harmonic, third harmonic).Output Leakage Current (ILEAKAGE)It means that the current enters the comparator output (the output is driven high). It often appears at the output of open collector and open drain.Power Supply Rejection Ratio (PSRR)It refers to the ratio of the change in the input offset voltage to the change in the power supply voltage, PSRR (dB) = 20log10 (DVOS / DVS)Linear Phase DeviationIt refers to how a closed-loop phase response of an operational amplifier approaches and follows the linear relationship between phase change and frequency in a specific frequency band.-3dbIt refers to the frequency when the value of the small signal output amplitude of the closed-loop amplifier decreases to 3dB.Common-mode Voltage RangeIt refers to the typical value of the voltage range at the input, which determines the performance of the amplifier.Specified Power Supply RangeIt describes the power supply voltage required for the operational amplifier to operate.Output Absorption CurrentIt refers to the highest output negative current of the comparator.Output Voltage SwingIt refers to the maximum peak-to-peak swing of the output voltage under a specific load and power supply voltage.Current FeedbackIt refers to a technology used in current feedback amplifiers whose output signal reflects the value of the current input to the inverting input (transimpedance gain function). In some aspects, this topology has operational advantages over traditional voltage feedback.Closed Loop BufferIt refers to an amplifier with high input impedance and low output impedance and a fixed gain of +1. Its typical applications are used for isolation, increased output drive, capacitive load, etc., in addition, there is no need to set the gain resistance.Closed-loop Gain It is the ratio of the change in the output voltage to the change in the input voltage after the feedback and input network added. Generally, this value is set using an external resistance.Common-mode RangeThe common-mode range, also known as the input voltage range, is a measure of the range of input voltages that the input pins of an op amp can accept. This specification is usually relative to the power supply amplitude.Output ImpedanceIt refers to the ideal series output impedance of the ideal operational amplifier when there is no impedance, which is the approximate output impedance of the op amp measured under AC  conditions.Transient ResponseIt refers to the step function response of the closed-loop system of the amplifier under the condition of small signal (usually less than 100mV).Slew RateWhen given a transition or square wave input, the amount of change in the amplifier's output from one level to another. Typical values are averages of values measured based on a change in total output voltage from 10% to 90%.Response TimeIt is the time interval when the input step function makes the output from the initial value to the logic threshold voltage.Unity Gain FrequencyIt refers to the frequency at which the gain of the voltage feedback op amp is 1 (0 dB). For an ideal operational amplifier, its gain-bandwidth product is equal.Intercept PointIt refers to the output power of the fundamental frequency, which is equal to the power value of the fundamental frequency in the specified distortion term (2nd, 3rd, or 3rd intermodulation).Input Offset CurrentIt refers to the current difference between the two inputs.Voltage OverdriveIt means that a certain amount of input step voltage exceeds the minimum drive input voltage required by the comparator to change from one logic level to the opposite logic level.Differential Gain & Differential PhaseDifferential gain refers to the change in the input and output of the gain, and differential phase refers to the phase change in the input stage. They are video measurements, and are a standard measurement in the broadcasting field to measure relative changes in the interpretation of video signal consistency.Voltage FeedbackA technique used in traditional operational amplifiers, where part of the output voltage is fed back to the input, and the voltage difference between the two inputs is amplified by the operational amplifier. Avol Open-loop Voltage Gain“A” is a sign of gain. The letter “V” written below indicates the gain of voltage, and the letter “ol” also written below is an abbreviation for open loop. Open-loop voltage gain refers to the gain (Vout / Vin) of the amplifier without feedback. Due to the existence of the bias voltage, these errors must be compensated.Logic Threshold VoltageIt refers to the voltage that causes the comparator output state to change when the input offset voltage is exceeded.Output ResistanceIt refers to the value of the series resistance at the output of an ideal op amp with zero output resistance, which measured under DC conditions.Gain FlatnessIt refers to the volume of gains “violently increasing” and “rapidly decreasing” in a given bandwidth range measured in decibels (dB), which affects the most important parameter specifications such as phase margin, gain margin, and closed-loop gain.Offset Current Temperature CoefficientIt refers to the average rate of change in deviation current due to changes in junction temperature within a specified temperature range.Input ImpedanceIt is the ratio of input AC voltage to input AC current.Input Voltage NoiseIt refers to the equivalent voltage noise in series with a noiseless amplifier.Input Offset VoltageIt is the product of the DC error voltage between the inputs and the closed-loop gain, because of the non-ideal balance between the input stage and the output is caused by the DC error voltage of the input terminals.Gain MarginOpen loop gain when the phase between the inverting input and output crosses zero at a certain frequency.Supply CurrentIt refers to the current required from the power supply to the unloaded amplifier and to the power supply at the output midpoint.Settling TimeIt refers to the time between the input step function initial value and the output voltage reaching the specified error band. The error band refers to the percentage of the total voltage change.Differential Input ResistanceIt is the ratio of the change in the input voltage to the change in the input current.Ⅲ Q & AQ1: What is the difference between a voltage feedback amplifier and a current feedback amplifier?A: The internal circuits of these two op amps are different. The voltage feedback op amp is restricted by the internal design, and it only has a very low input bias current, but there is no internal limit on the differential input voltage, because it is limited only when external feedback is required. In contrast, for a current feedback amplifier, its differential input voltage is subject to internal design, but it does not limit its input bias current, so it is limited only when external feedback is required.Q2: What is the difference between open and closed loops?A: The open loop gain is actually the internal gain of the op amp without feedback, and usually takes any value between 1,000 and 10,000. Closed loop gain is the gain of the entire circuit, which is equal to the open loop gain divided by 1 plus the loop gain (the improvement coefficient). In fact, the gain of the op amp when there is no feedback is the open loop gain, and the gain when feedback is considered is closed-loop gain.Q3: If the op amp has ideal AC characteristics, the Bode plot (gain-frequency response) is a unipolar system. What is the gain slip rate in dB / decade?A: In a unipolar system, the gain drops (or decreases) at 20dB / decade, which is 6dB / octave. This is responsive to any single pole, and it is also suitable for a simple RC filter or an ideal operational amplifier. However, because op amps have more high-frequency poles, the phase shift will begin to increase as the frequency approaches the unity gain frequency of the op amp.Q4: What is the difference between unity gain bandwidth, gain bandwidth product (GBP), and -3dB frequency?A: Many op amps have an open-loop gain reduction rate of -20db / decade when the frequency is stable. At any point during this descent phase, the GBW is a constant. If the unity-gain operation of the op amp is stable, then the unity-gain bandwidth, or the frequency at which the open-loop gain is 1, is usually equal to GBP. In addition, GBP is not equal to (usually higher than) the unity gain bandwidth. The -3dB frequency is a measure of the bandwidth of an operational amplifier when it is operating in a closed loop. The -3dB point is the frequency at which the gain of the overall closed-loop system drops by 3dB. The unity gain frequency for closed loop applications can be calculated using BW=GBP/Av. The -3dB frequency and unity-gain bandwidth applied depend on the feedback gain setting, output swing, load, and circuit layout.Q5: Why do some amplifiers oscillate with a capacitive load?A: The output impedance of the op amp and the capacitance of the capacitive load may form a resistance-capacitance oscillation. Also they form an R-C oscillation at the output stage, which causes additional phase lag in the feedback signal. CMOS amplifiers have a high output impedance which will cause the electrodes to be approached or lower the unity gain frequency of the op amp. The additional phase lag of the electrodes will weaken the phase margin of the op amp The total phase lag of the amplifier causes the phase angle of the unity gain frequency to increase by more than 180 degrees to cause the total feedback phase shift in unity gain to exceed 180. degree. In addition, the output impedance of a CMOS amplifier is between 100 and 500, causing a relatively low pole frequency. And meanwhile, the output impedance of the high-speed bipolar operational amplifier is in the range of 1 to 100, which causes the pole frequency to be much higher than that of the CMOS operational amplifier, so that the pole is far from the unity gain frequency of the device. The drive of a CMOS amplifier to a capacitive load can be improved by placing an output resistor at the output and an external positive feedback capacitor.Q6: If the output of the op amp stays close to the voltage rail, that is, the output rail, what is the reason?A: There are many ways for operational amplifiers to “rail”. The difficulty is keeping it away from the "rail". If the input exceeds the input voltage range, the output is usually near to a supply voltage rail. In theory, if the output exceeds the actual supply voltage, and a higher supply voltage is given, the op amp will go to rail output again. If there is no feedback or the polarity of the feedback is wrong, the op amp goes to rail output again. At the same time, if the non-inverting input is higher than the negative inverting input, the op amp also goes to rail output. The application of the operational amplifier should be analyzed to ensure that the power supply voltage used has a proper input and gain, so that in normal operation, its input voltage is within the rated value and the output voltage is within the normal range.Q7: What is the difference between the common-mode voltage and input voltage range of an op amp?A: Common mode voltage means that one voltage is applied to both inputs at the same time. Input voltage range is the range of voltages that can be accepted by the input pins. It is necessary to remember that the op amp should suppress the common-mode voltage, and amplify the difference between the two input pins only.Q8: The SPICE model of the bipolar operational amplifier works well, but the SPICE model of the CMOS operational amplifier does not work. Is there a need to set SPICE?A: To input the appropriate bias current to the model, the SPICE model applied on CMOS operational amplifier needs to set the default GMIN option to the largest SPICE package value.Q9: What is the difference between the amplifier's output current and short-circuit current?A: Short circuit current refers to the current generated by the device if the output is connected directly to the power line. This indicates that the output current is limited depending on the design of the device. However, the short-circuit current does not represent the true output of the drive capability of the output. Due to the impedance characteristics of the output stage, the maximum output current is determined by the swing of the output voltage under load. In facet, the smaller the load, the larger the output swing; the larger the load, the smaller the output swing.Q10: How to check the stability of an op amp circuit?A: Check the stability of the control loop, such as the pulse load and related changes in output voltage. The pulse load may be a load current with a pulse or step change, so that the output of the op amp circuit should be connected to a series R-C circuit. The greater the circuit swing or vibration, the worse the stability of the circuit.Q11: Are there any good ways to minimize noise when amplifying a low-level DC signal?A: To obtain a high signal-to-noise ratio, the circuit must be well designed. This includes choosing the best amplifier bandwidth and knowing the impedance of the input signal. If the input signal source has a fairly high impedance, it makes no sense to choose a low voltage noise amplifier, which has high current noise.Q12: How should design a low frequency (<1Hz) differentiator to minimize the output noise?A: The only reason that the output of the differentiator contains noise is because there is a lot of gain and the input is noisy. The traditional differentiator uses Rs-Cs in series at the input and the Rf-Cf in parallel near the operational amplifier. It is not necessary to try more Rs or Cf to minimize noise. The noise of the output come from the differentiator does not mean that it is harmful, because it also amplifies useful signals. In addition, if disconnect a loop, the differential output noise may be beneficial and will stabilize the loop. If the output of the differentiator is quite noisy or has too much input noise, analyze which are the real sources of them.Q13: How to protect the amplifier input from being higher or lower than the supply voltage?A: What must be done is either to clamp the input of the device, or to limit the input current of the device, or ideally, do both. The easiest way is to choose a current limiting resistor to limit this current. The selection is based on the fact that the current generated by the circuit input at the maximum input voltage is less than the maximum current rating of the input pin. Usually, a 1K to 100K resistor in series with this input pin is effective. However, since the signal is usually connected directly to a non-inverting input pin, a non-inverting amplifier may need a protective resistor connected to this pin. For high impedance circuits, a large resistor and or low leakage current diode can be used.Q14: What is the difference between a single-supply amplifier and a dual-supply amplifier?A: There is no difference in the actual circuit, layout, and characteristics of the amplifier. When an operational amplifier is designated as dual power supply, the output load is usually referenced to ground (GND), while a single power supply operational amplifier is usually referenced to the midpoint voltage of a single supply, and it is usually specified to operate on lower voltages, but this is not a necessary requirement. Therefore, whether the op amp is powered by a single 5V power supply and ground (GND), or powered by +2.5 and -2.5V, these is no different. Ⅳ Application: LM358 Classic CircuitsThis Video is Going to Show Top 5 Electronics Project Using OP-AMP LM358The LM358 includes two independent, high-gain, internal frequency-compensated dual operational amplifiers. It is suitable for single-supply operation with a wide range of power supply voltages. It is also suitable for dual-supply operation. LM358 applications include sensor amplifiers, DC gain modules and all other operational amplifiers that can be powered by a single power supply. The classic circuits of LM358 are as shown as following:Figure 1. Active DC-coupled Low Pass RC Filter Figure 2. LED Driver Figure 3. Transistor-Transistor-Logic (TTL) Drive Circuit Figure 4. Active RC Band Pass Filter Figure 5. Squareware Oscillator Figure 6. Hysteresis ComparatorFigure 7. Active Band Pass filter Figure 8. Lamp Driver Figure 9. Current Monitor Figure 10. Low Drift Peak Detector Figure 11. Voltage Follower Figure 12. Power Amplifier Peripheral CircuitFigure 13. Voltage Controlled Oscillator VCOFigure 14. Fixed Current Source Figure 15. Pulse Generator Figure 16. AC Coupled Non-inverting Amplifier Figure 17. AC Coupled Inverting Amplifier Figure 18. Adjustable Gain Instrumentation Amplifier Figure 19. DC Amplifier Figure 20. Pulse Generator Figure 21. Bridge Current Amplifier Figure 22. Introducing Differential Input Signal Figure 23. DC Differential Amplifier Frequently Asked Questions about Op Amps Basics1. What is an op amp basics for dummies?An op amp is a super-sensitive electronic amplifier circuit that's designed to amplify the difference of two input voltages. Thus, an op amp has two inputs and one output. ... Most op amps require both a positive and a negative voltage power supply, with voltages usually ranging from 6 V to 18 V. 2. What is the basic use of op amp?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 3. What is operational amplifier and its types?An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Op amps usually have three terminals: two high-impedance inputs and a low-impedance output port. 4. Which purpose the op amp is used?As the name suggests, the purpose of an amplifier or an op amp is to amplify or increase the input signal to produce an output signal which is much larger than that of the input, with a similar waveform as that of the input. The main change in the output signal will be the increase in the power level. 5. What does it mean when an op amp saturates?Originally Answered: What happens when an op-amp is saturated? that means the amplification or gain is so high as to make the output signal with a given input signal, so large as to exceed the compliance range of the power supply of the ope amp. More simply put, if you have an op amp supplied with +/-15V supply rails.

Ⅰ IntroductionAs we all know, capacitors have always played a very important role in electronic circuits. They are responsible for the coupling of signals in electronic circuits, the differentiation of volt-ampere characteristics in RC circuits, such as integration, the "channel" in oscillating circuits, bypass and power filter, etc. Aluminum electrolytic capacitor is made of anodized aluminum foil, corroded cathode aluminum foil and electrolytic paper in the middle, then impregnated with working electrolyte and sealed in aluminum shell. CatalogⅠ IntroductionⅡ Common problems of electrolytic capacitor  2.1 Why can't an aluminum electrolyte capacitor withstand reverse voltage?  2.2 What are the similarities and differences between nonpolar capacitance and polar capacitance?  2.3 What will happen when a polar capacitor is reversed?  2.4 The reverse connection of the polar capacitor will explode. Does it mean that it can't be directly connected to the AC power supply?  2.5 If the polarity capacitor is reversed, why is it short-circuited?  2.6 Why does the resistivity of electrolytic capacitor become smaller when the positive and negative poles are reversed?  2.7 Why can we only use a nonpolar capacitor in a pure AC circuit?  2.8 What is electrolytic capacitance?  2.9 The characteristics of electrolytic capacitors are as follows  2.10 What are the similarities and differences that cannot be ignored between polar and nonpolar capacitors in performance, principle and structure?Ⅲ SummaryⅣ FAQ Ⅱ Common problems of electrolytic capacitor2.1 Why can't an aluminum electrolyte capacitor withstand reverse voltage?Due to the polarity of electrolytic capacitors, it is necessary to pay attention to the correct connection of positive and negative electrodes in use, otherwise, not only the capacitors can not play a role, but also the leakage current is very large. In a short time, the inside of the capacitors will heat up, damage the oxide film, and then damage.  As shown in the figure, the basic structure of the aluminum electrolytic capacitor is composed of an anode, aluminum layer attached to the insulating medium, cathode aluminum layer of the receiving electrode and the real cathode composed of electrolyte. The electrolyte is soaked in the paper between the two aluminum layers. Aluminum oxide layer is plated on the aluminum layer, which is very thin compared with the voltage applied on it, and it is easy to be broken down, leading to capacitor failure. The alumina layer can withstand the forward DC voltage. If it bears the reverse DC voltage, it is easy to fail in a few seconds. This phenomenon is called the "valve effect", which is why the aluminum electrolytic capacitor has polarity. If both electrodes of the electrolytic capacitor have an oxide layer, the non-polar capacitor will be formed.Many articles report the mechanism of the threshold phenomenon of the reverse voltage of the aluminum electrolytic capacitor, which is called the hydrogen ion theory. When the electrolytic capacitor bears the reverse DC voltage, that is, the cathode of the electrolyte bears the positive voltage while the oxide bears the negative voltage, The hydrogen ions gathered in the oxide layer will pass through the medium and reach the boundary between the medium and the metal layer, and then they will be converted into hydrogen. And the expansion force of the gas causes the oxide layer to fall off. Therefore, the current flows directly through the capacitor after breaking through the electrolyte, and the capacitor fails. This DC voltage is very small. Under the reverse DC voltage of 1 ~ 2V, the aluminum electrolytic capacitor will immediately fail due to the hydrogen ion effect in a few seconds. On the contrary, when the positive voltage is applied to the electrolytic capacitor, the negative ions are concentrated between the oxide layers. Because the diameter of the negative ions is very large, they can not break through the oxide layer, so they can withstand higher voltage.2.2 What are the similarities and differences between nonpolar capacitance and polar capacitance?Are nonpolar capacitors the same as nonpolar electrolytic capacitors? Most kinds of capacitors are nonpolar, only the electrolytic capacitors have polarity. Among them, there are very special nonpolar electrolytic capacitors. Compared with ordinary capacitors, electrolytic capacitors have a larger capacity, lower price and smaller volume than other capacitors, but electrolytic capacitors generally have polarity, and their working reliability, withstand voltage, temperature resistance, dielectric loss and other indicators are not as good as other capacitors.The so-called non-polar electrolytic capacitor is actually the back-to-back packaging of two identical electrolytic capacitors. This kind of capacitor has large loss, low reliability and low voltage withstand, which can only be used in a few occasions with low requirements.2.3 What will happen when a polar capacitor is reversed?If the capacitance capacity is very small, the withstand voltage is very high, and the working voltage is low, there will be nothing wrong with the reverse connection. If the capacity is slightly large (above 100uF) and the withstand voltage is close to the working voltage, the capacitance can just work for nearly 10 minutes, then it will bulge and burst.2.4 The reverse connection of the polar capacitor will explode. Does it mean that it can't be directly connected to the AC power supply?It can't be connected to the AC power supply, because the polar capacitor is designed to be used in the DC power supply for filtering, and there is special material inside the polar capacitor, which can not bear the backpressure. If it is connected to the AC power supply, it will breakdown reversely or explode.2.5 If the polarity capacitor is reversed, why is it short-circuited?The internal structure of the polar capacitor is divided into the positive electrode, a dielectric layer and the negative electrode. The dielectric layer has the property of unidirectional conduction. Of course, the dielectric layer of the product will not play the role of insulation after being connected reversely, and the capacitor will be short-circuited. 2.6 Why does the resistivity of electrolytic capacitor become smaller when the positive and negative poles are reversed?It involves the principle of electrolytic capacitor. When the positive electrode of the capacitor is connected positively, a very thin oxide film (alumina) will be formed as the dielectric. When the negative electrode of the capacitor is connected reversely, H2 will be produced without forming the oxide film, and the other electrode will not form the oxide film which can be used as the dielectric due to different materials. 2.7 Why can we only use a nonpolar capacitor in a pure AC circuit?In the circuit of DC voltage superposing AC signal, if we can ensure that the lowest voltage after superposing will not become negative, we can use a capacitor with polarity. In the case of the same capacity, the volume and cost of the polar capacitor are far less than that of the nonpolar capacitor, so when we need a larger capacity, the volume of the capacitor is a big contradiction. We usually replace non-polar capacitors with polar ones, which not only solves the volume problem but also reduces the cost. Large capacitance can filter the AC signal with a lower frequency and above, while small capacitance can only filter the signal with higher frequency and above. 2.8 What is electrolytic capacitance?Electrolytic capacitor is a kind of capacitor. Its medium is coated with electrolytes. It can be divided into positive and negative electrodes and cannot be connected wrongly. The capacitance is composed of two metal poles and the insulating material (medium) sandwiched between them.2.9 The characteristics of electrolytic capacitors are as follows①The capacitance per unit volume is dozens to hundreds of times larger than other kinds of capacitance.②Rated capacity can easily reach tens of thousands of μ for even several F, but it is not as good as double electric layer capacitance.③The price is much lower than other kinds because the components of electrolytic capacitors are ordinary industrial materials, such as aluminum. The equipment for manufacturing electrolytic capacitors is also common industrial equipment, which can be mass-produced at a relatively low cost. Electrolytic capacitors are usually made up of metal foil (aluminum/tantalum) as the positive electrode, and the insulating oxide layer (alumina/tantalum pentaoxide) of metal foil as the dielectric. The negative electrode of aluminum electrolytic capacitor is composed of thin paper/film or electrolyte polymer soaked in electrolyte, the negative electrode of the tantalum electrolytic capacitor is usually manganese dioxide. As both of them use electrolytes as the negative electrodes, the electrolytic capacitor gets its name. The polar electrolytic capacitor usually plays the role of power filter, decoupling, signal coupling, the time constant setting, DC isolation and so on in the power circuit or IF and LF circuits. It can't be used in an AC power circuit. When it is used as a filter capacitor in the DC power circuit, its anode (positive) should be connected with the positive end of the power voltage, and the cathode (negative) should be connected with the negative end of the power voltage. It can't be reversed, or it will be damaged. 2.10 What are the similarities and differences that cannot be ignored between polar and nonpolar capacitors in performance, principle and structure? Polar capacitance is a kind of electrolytic capacitance. It consists of two electrodes formed by the anode aluminum foil and the cathode electrolyte. A layer of aluminum oxide film produced on the anode aluminum foil is used as the dielectric of capacitance. As a result of this structure, it has polarity. When the capacitance is directly connected, the aluminum oxide film will remain stable due to the electrochemical reaction. When the reverse connection is made, the aluminum oxide layer will become thinner, which makes the capacitor easy to be broken down and damaged.  Therefore, we must pay attention to the polarity of the electrolytic capacitor in the circuit. Ordinary capacitors are nonpolar. We can also connect two anodes or cathodes of electrolytic capacitors in series to form nonpolar electrolytic capacitors. ①The same principleThey both store and release charges.The voltage on the plate shall not change suddenly. (voltage here refers to the electromotive force of charge accumulation) ②Different mediaWhat's the medium? It's the material between the two plates of the capacitor. Most of the polar capacitors use electrolytes as a dielectric material, and the capacity of the polar capacitor is larger than that of the same volume. In addition, the capacity of the same volume of polar capacitance produced by different electrolyte materials and processes will be different. The withstand voltage of the capacitor is closely related to the dielectric materials used. There are also many dielectric materials for non-polar capacitance, most of which are metal oxide film, polyester and so on. The reversibility or irreversibility of dielectric determines the use environment of polar and nonpolar capacitors. ③Different performance.Performance and maximization of requirements are the requirements for use. If a metal oxide film capacitor is used for filtering in the power supply part of the TV set, and the capacity and withstand voltage of the capacitor should meet the requirements of filtering, a power supply must be installed in the shell. For a filter, only the polar capacitance can be used, which is irreversible. The positive terminal must be connected to the high potential terminal and the negative terminal to the low potential terminal. Generally, when the electrolytic capacitance is more than 1 microfarad, it is used for coupling, decoupling, power filtering, etc. Most of the nonpolar capacitors are below 1 microfarad, which participates in resonance, coupling, frequency selection, current limiting, etc. Large capacity and high withstand voltage capacitors are usually used for reactive power compensation, motor phase-shifting and frequency conversion power supply phase-shifting. There are many kinds of nonpolar capacitors. ④Different capacityFor capacitors of the same volume, when the medium is different, the capacity is also different. ⑤Different structureWe can use capacitors of any shape without considering the tip discharge. The polar capacitance is usually round, and there are few polar capacitances of square type. There are many shapes of nonpolar capacitors, including tube type, deformed rectangle, sheet type, square type, circular type, combined square type and circular type, and of course there are intangible ones. Here intangible refers to distributed capacitance.The distributed capacitance in HF and IF devices should not be ignored. The function is the same. The main difference is their capacity. Due to the influence of material structure, the capacity of non-polar capacitance is relatively small, generally below 10uF, while the capacity of polar capacitance is usually large. When filtering the power supply, you have to use a polar capacitor of large capacity. Ⅲ SummaryOne of the basic principles of circuit design is to require the designer to fully understand and master the real components. The components used should be standard parts, general parts, and the most common models on the market (the better the versatility of components, the easier the procurement, the larger the supplier's output, and the lower the procurement cost). For the components used in the drawings, if the materials can only be obtained by customization, the cost is certainly not low. If you can't get the customized material, this design is wastepaper. In addition, large capacitance is suitable for filtering low-frequency signals and small capacitance for filtering high-frequency signals. However, decoupling is only one function of capacitance. Different kinds of capacitance have different characteristics and usages. This aspect has a lot to do with experience. It is impossible to achieve it quickly. It can only be accumulated through practice. Ⅳ FAQ1. Which capacitor gives a long-term service: ceramic capacitors or aluminum and tantalum electrolytic capacitors?Electrolytics have a limited lifetime, 10,000 hours at high temps.Tantalums are really good capacitors, until they short out, whenever they feel like it.Ceramics tend to live the longest. 2. Why is aluminum used in electrolytic capacitors?Aluminum has been found to be among ideal materials for electrolytic capacitors due to the following reasons—1) It easily forms a thin oxide layer with a high dielectric constant.2) This layer can be formed in a wide range of thicknesses to suit different applications.3) The aluminum oxide layer can be formed and can withstand high voltages exceeding 400 V. Other materials Tantalum/ Niobium can only take small voltages of below 25 V. 4) Aluminum can be made into foil/ plate / formed into shape. In yesteryears, it was common to use shapes of this metal mechanically formed into different shapes.5) These properties allow high capacitor values for low and high voltages in small size.6) Most amenable to convenient manufacturing processes like winding, punching, forming (oxidation).7) Most abundant material on earth, hence very cheap.There are hardly any other materials that have these properties. 3. What is the role of aluminum electrolytic capacitors?Aluminum electrolytic capacitors are polarized capacitors because of their anodization principle. They can only be operated with DC voltage applied with the correct polarity. Operating the capacitor with the wrong polarity or with AC voltage leads to a short circuit and can destroy the component. 4. What happens if the electrolytic capacitor backward?Electrolytic capacitors are polar by nature and have positive and negative terminals clearly marked. If the polarity is reversed while connecting, the dielectric in the form of an oxide layer is damaged. A heavy current flows, a large amount of heat is generated, and the capacitor is damaged. 5. How do you determine the polarity of the Aluminium electrolytic capacitor?If the case is insulated, you can try applying a small bias voltage (3-5V) to the capacitor in each direction (through a current-limiting resistor of 100K or so) and see which direction allows the least current; this will be the correct polarity of the capacitor. 6. What are aluminum electrolytic capacitors used for?Especially aluminum electrolytic capacitors are used in many applications as decoupling capacitors to filter or bypass undesired biased AC frequencies to the ground or for capacitive coupling of audio AC signals. Then the dielectric is used only for blocking DC. 7. How long do aluminum electrolytic capacitors last?Today's aluminum electrolytic capacitors have a longer shelf life, usually around 2 years, as compared to their predecessors. For aluminum electrolytic capacitors, the changes in ESR, capacitance, and leakage current are caused by the chemical reactions between the aluminum oxide film and the electrolyte. 8. How do you read an electrolytic aluminum capacitor?The value of the capacitor is denoted in picofarads for ceramic, film, and tantalum capacitors, but for aluminum electrolytic capacitors the value is denoted in microfarads. For small values the letter R is used to denote a decimal point, e.g. 0R5 is 0.5, 1R0 is 1.0 and 2R2 is 2.2, etc. 9. How are aluminum electrolytic capacitors made?Aluminum electrolytic capacitors are made by layering the electrolytic paper between the anode and cathode foils and then coiling the result. The process of preparing an electrode facing the etched anode foil surface is extremely difficult. Due to this process, the electrolyte essentially functions as the cathode. 10. What are aluminum capacitors used for?Aluminum electrolytic capacitors (electrolytic) are widely used in power supply applications requiring high capacitance in energy-dense, small-volume packages having very low equivalent series resistance (ESR).