The Kynix Blog - Capacitors

Introduction Capacitors are now commonly used as decoupling capacitors, DC blocking capacitors, or as matching capacitors due to their characteristics of blocking DC while passing AC. But in practical applications, DC can charge the capacitor and pass through it. Is this contrary to its characteristics? Why can DC charge the capacitor? Here we will discuss this issue in details. Charging and Discharging of Capacitor -RC Circuit Catalog Introduction Ⅰ Capacitor Charging Principle Ⅱ Why Capacitor Charges in DC? Ⅲ Capacitor Transient and Steady-state Processes Ⅳ Capacitor Circuit Analysis and Calculations Ⅴ FAQ Ⅰ Capacitor Charging Principle A capacitor is a component that can store electrical energy. As one of the most commonly used electronic components, the simplest capacitor is composed of plates at both ends and an insulating dielectric (including air) in the middle. After being energized, the plates are charged to form a voltage (potential difference), but due to the insulating material in the middle, the entire capacitor is non-conductive. However, this situation is under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded. In fact, any substance is relatively insulating. When the voltage across the substance increases to a certain level, the substance can conduct electricity. We call this voltage breakdown voltage.It is the same for the capacitor. After the capacitor is broken down, it is not an insulator. In an AC circuit, because the direction of the current changes with time as a certain function. The process of charging and discharging a capacitor takes time. At this time, a changing electric field is formed between the plates, and it is also a function of time. So current passes between capacitors in the form of an electric field.Capacitors are similar to batteries in that they also have two electrodes. Inside the capacitor, the two electrodes are connected to two metal plates separated by a dielectric. When the capacitor is connected to the power supply, under the action of the electric field force, the free electrons of the capacitor plate connected to the positive electrode of the power supply will move to the negative electrode. The positive electrode is positively charged due to the loss of negative electrons, and the negative electrode is negatively charged due to its negative electrons. In addition, the charges on the positive and negative plates are equal, with opposite signs.The directional movement of the charge forms a current. Due to the repulsion of the same charges, the current is the largest at first, and then gradually decreases. During the charge movement, the charge stored in the capacitor plate continues to increase, and the charge stops moving when the voltage between the two plates of the capacitor is equal to the power supply voltage. That is, the current I=0, the switch is closed, and the positive and negative plates of the capacitor are neutralized through the connection of the wires. When the switch is closed, the positive charge of the positive pole of the capacitor can be moved to the negative pole and neutralized. When the charge gradually decreases, the current decreases, and the voltage gradually decreases to zero.   Ⅱ Why Capacitor Charges in DC? Why is there a charging current that lasts for a period of time when using DC to charge a capacitor? At this time, the circuit is equivalent to an open circuit, there is no continuous current without a loop, and the capacitor charging has time, not instantaneously, so the instantaneous current is not the answer. Having a potential difference, how does a circuit without a closed loop produce a charging current that lasts for a period of time? Figure 1. Transition Process When Charging the Capacitor The voltage across the capacitor is not allowed to change suddenly. So when the power is turned on, the voltage across the capacitor is equal to zero, and then the voltage rises exponentially until it enters a steady state. The capacitor after entering the steady state is equivalent to an open circuit. In fact, the capacitor can block the constant direct current and disconnect when it fully charged in the circuit. According to the leakage resistance of the capacitor, the charge can be stored in the capacitor for a long period of time.When Usr is instantly added to the resistor-capacitor circuit, because the voltage across the capacitor is not allowed to change suddenly, the capacitor is equivalent to being short-circuited at this time. So at time 0, the current flowing through the capacitor and resistor R is .Then the capacitor began the charging process, and the current became smaller and smaller. After 5 times the RC time, the capacitor charging is basically over and the current is reduced to zero. Since then, it has entered a steady state. The RC(τ) here is called the time constant.We know that resistance is equal to the ratio of voltage to current, that is, R=U/I. We also know that the capacitance C is equal to the ratio of the electric quantity Q to the voltage U, and the electric quantity Q is equal to the product of the current I and the time t .It turns out that the product of resistance and capacitance is time. The unit of resistance is ohms and the unit of capacitance is farads, so the unit of time is seconds.In Figure 1, when the capacitor is charged, the voltage across it is .We find Uc when t=0, 1RC, 2RC, 3RC, 4RC, and 5RC, as follows: It can be seen that when time t=0, the voltage across the capacitor is equal to zero; when t=5RC, the voltage across the capacitor is almost equal to the input voltage.Let's look at the current flowing through the capacitor, its expression is as follows: When t=5RC, where .It can be seen that the current at this time is almost equal to zero. Therefore, the transient process and steady-state process of the capacitor must be clearly distinguished.   Ⅲ Capacitor Transient and Steady-state Processes 1) There are transient and steady-state processes in the capacitor charging circuit.2) At the beginning of capacitor charging, it must be considered that the voltage across the capacitor does not allow sudden changes, which is an important principle.3) The transient process generally ends after 5τ.4) For Figure 1, at the moment of the transient start, the capacitor voltage Uc is equal to zero, and the current Ic is equal to the maximum value. We know from Ohm's law that the equivalent resistance of the capacitor is equal to zero . Usually we say that the capacitance at this time is equal to the short circuit i. In the steady state at the end of the transient, the capacitor voltage Uc is equal to the input voltage Usr, and the capacitor current Ic=0. According to the Ohm's law that the equivalent resistance of the capacitor is equal to infinity . At this time, the capacitance is equivalent to an open circuit.5) If the input signal voltage is a short pulse, the capacitor can transmit the signal to the load; if the input signal is a constant voltage, the capacitor will only respond during a short transition, and then block the input signal; if the input signal is an AC signal, which is exactly in the middle of the above two situations.The higher the frequency of the AC signal, the easier it is to pass through the capacitor. We call this feature a high-pass filter function. Although the AC signal can pass through the capacitor, there will be a certain amount of clipping. This shows that the capacitor has the function of isolating DC in the steady state, and a high-pass characteristic. So we can further analyze, any circuit with capacitor and inductor, we must analyze the circuit according to the transient state and the steady state, in order to get the correct analysis result.   Ⅳ Capacitor Circuit Analysis and Calculations The analysis is available from the figure below: Figure 2. Output Voltage Usc If set Usr=10Vdc, the capacitance is equal to 10 microfarads, and the resistances R1 and R2 are both 1 kiloohm, then how to analyze the value of Usc?Step 1: Determine the time constant of the capacitor. Figure 3. Usr in Short-circuit Connection From the analysis of the above figure, it can be seen that the time constant is 20 milliseconds , and the time for 5 times the time constant is 0.1 seconds.Step 2: Let's calculate the specific value of Usc.When Usr in Figure is just established, the capacitor voltage drop is equal to zero, so there is .After 5τ, the capacitor is full of voltage, and its value is Uc=Usr, so Usc=0, .When charging starts, t=0, When the time has passed 0.1 second, we have , and the Usc at this time is almost equal to zero. Now, let's connect R1 and C in parallel, and see what happens: Figure 4. R1 and C are Connected in Parallel We see that if Usr in the figure is short-circuited, R1 and R2 are connected in parallel, so the time constant is At the beginning of Usr power on, C is equivalent to a short circuit, and Usr is directly loaded on both ends of the resistor R2, so at this time Usc=UseWhen the circuit enters a steady state, Usc is equivalent to the partial pressure of Usr by resistors R2 and R1, namely Based on this, we can derive the following equation: .In the above formula, the first term on the right side of the equal sign is the change in capacitor voltage, which reflects the transition process. The second term on the right side of the equal sign is the final steady-state voltage.Substitute the parameters, and calculate the time constant first: .In other words, when the time is 5τ, that is, 25 microseconds, the output voltage tends to stabilize. The final value is .It is still 5V, but the transition process is only 25 microseconds, which is much shorter than the previous 0.1 second.   Ⅴ FAQ 1. When a capacitor is charging in a DC circuit?At this point, the electric field between the plates cancels the effect of the electric field generated by the battery, and there is no further movement of charge. Thus, if a capacitor is placed in a DC circuit then, as soon as its plates have charged up, the capacitor effectively behaves like a break in the circuit.   2. What happens to the current in a DC circuit once a capacitor is charged?For a capacitor charge Q = capacitance C multiplied by voltage V. This quite simply means that a rate of change of voltage gives rise to a current. If the voltage is rising linearly with time, the capacitor will take a constant current and once the voltage stops changing the current is zero.   3. Does current flow in a DC circuit while a capacitor is charging?Yes. For DC circuits, when a capacitor is charged or discharged, current is flowing into and out of it. For AC circuits, a capacitor can act almost like a "resistor" but instead it is called reactance. But alas, current does flow through the capacitor.   4. Do capacitors charge with AC or DC?When DC current is applied to a circuit with only resistance and capacitance, the capacitor will charge to the level of the applied voltage. Since DC only flows in one direction, once the capacitor is fully charged there is no more current flow.   5. Can we use capacitor in DC?Capacitors can be used in many different applications and circuits such as blocking DC current while passing audio signals, pulses, or alternating current, or other time varying wave forms. ... At DC a capacitor has infinite impedance (open -circuit), at very high frequencies a capacitor has zero impedance (short-circuit).   6. Can a capacitor be charged by DC?When capacitor is connected to dc voltage source, capacitor starts the process of acquiring a charge. This will built up voltage across capacitor. Once capacitor has acquire enough charge, current starts flowing and soon capacitor voltage reaches at value approximately equal to dc source voltage.   7. Why does AC pass through capacitor but not DC?Capacitors have two parallel metallic plates placed close to each other and there is a gap between plates. A capacitor blocks DC but it allows AC. ... Therefore the electrons flowing in one direction (i.e. DC) cannot pass through the capacitor. But the electrons from AC source seem to flow through C.   8. What happens when capacitor is connected to DC?When capacitors are connected across a direct current DC supply voltage, their plates charge-up until the voltage value across the capacitor is equal to that of the externally applied voltage. ... Then the Capacitance in AC circuits varies with frequency as the capacitor is being constantly charged and discharged.   9. Why capacitor is used in DC circuit?Capacitors are useful to reduce the voltage pulsation. When the high voltage is applied to the parallel circuit, the capacitor is charged, and on the other hand, it is discharged with the low voltage. While electricity flowing out is alternating current, most of electronic circuits work with direct current.   10. Why do capacitors block DC current?We know that there is no frequency i.e. 0Hz frequency in DC supply. If we put frequency “f = 0″ in the inductive reactance (which is AC resistance in capacitive circuit) formula. If we put XC as infinity, the value of current would be zero. That is the exact reason why a capacitor block DC.   11. How is a capacitor charged in a DC circuit?When used in a direct current or DC circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and basically an insulator. ... At this point the capacitor is said to be “fully charged” with electrons.   12. Which capacitor is used in DC circuit?Decoupling capacitor is used, where we have to decouple the two electronics circuits. In other words, the noise generated by one circuit is grounded by decoupling capacitor and it does not affect the performance of other circuit.   13. Can you charge a capacitor with DC current?A DC voltage source is used to charge a Capacitor. When the DC voltage source is outputting more than the DC voltage source can charge, the Capacitor will charge up. Capacitors will charge up to 9 volts if they are connected to a 9-volt battery.   14. What happens if DC is applied to capacitor?When capacitors are connected across a direct current DC supply voltage, their plates charge-up until the voltage value across the capacitor is equal to that of the externally applied voltage. ... Then the Capacitance in AC circuits varies with frequency as the capacitor is being constantly charged and discharged.   15. Can we charge capacitor with DC current?When capacitor is connected to dc voltage source, capacitor starts the process of acquiring a charge. This will built up voltage across capacitor. Once capacitor has acquire enough charge, current starts flowing and soon capacitor voltage reaches at value approximately equal to dc source voltage.

Introduction As a beginner, what the functions of capacitors in a circuit? A Capacitor is a passive electronic component that stores and releases the energy. Its unique characteristic is blocking direct current while allowing alternating current to pass. The main functions of capacitors are based on these characteristics. The use of capacitors is also based on this. Here are collecting 20 questions about capacitor use in electronics enclosed with details. Let you have a more comprehensive understanding of the use of capacitors. How Capacitors Work? 20 Questions about the Role of Capacitors in Circuits Help you learn about capacitors functions in 30 minutes. These questions forcus on how capacitors work, where capacitors are used, why capacitors are used, the different types. 1) What is the function of a capacitor connected in parallel with the positive and negative terminals of the voltage source?When cap used in a rectifier circuit, it has a good filtering effect. When the voltage is alternating, the voltage at both ends cannot be changed suddenly due to the charging effect of the capacitor, which ensures the stability of the voltage. When cap used as a battery power supply, it is equivalent to short-circuiting the battery's AC signal, avoiding the increase in battery internal resistance and parasitic oscillation of the circuit due to the battery voltage drop. 2) A capacitor in series or in parallel can achieve the effect of coupling in the circuit. What is the difference between whether there is a capacitor in the circuit?In the AC multi-stage amplifying circuit, because of the different gains and powers of each stage, the DC working offset values of each stage are different. If the levels are directly coupled, it will cause the bias values of all levels to be mixed and unable to work normally. The “Pass AC, Block DC” characteristic not only solves the coupling of inter-stage exchanges, but also isolates the inter-stage biased value intermixing. 3) The two coupling capacitors in the basic amplifying circuit, the positive pole of the capacitor and the DC positive pole are connected to pass the AC and block the DC. Can the reverse connection also have this function?If the connection is reversed, the electrolytic capacitor will leak, which will change the DC operating point of the circuit and make the amplifying circuit abnormal or unable to work. 4) What is the role of the capacitor in the resistance-capacitance coupling amplifier circuit?Block the DC signal so that the static operating points of adjacent amplifying circuits are independent of each other and do not affect each other. 5) Can the analog circuit amplifier do not have a coupling capacitor? The theory in amplifier circuit adds a coupling capacitor between the transformer secondary coil and the transistor. Turn the output of the former stage into the input of the latter stage, so that two stages do not affect. The former stage is alternating current, so does the latter stage, so there no mutual influence.The former stage is indeed alternating current, but the latter stage is alternating current superimposed direct current. The transistor needs a DC bias. If there is no capacitor to block the DC, the coil of the transformer will bypass the DC bias of the transistor (because the inductor passes DC). 6) In the basic amplifier circuit, can the coupling capacitor be non-polar?In the basic amplifying circuit, the coupling capacitor depends on the frequency. When the frequency is high, a non-polar capacitor is needed. It is characterized by relatively stable, high withstand voltage, small size and capacity. Its biggest use is to block direct current and pass alternating current. Coupling capacitor is widely used in high-frequency alternating current paths, bypass, resonance and other circuits. (high-pass)When the frequency is low, since the capacitance of the non-polar capacitor is relatively low, the capacitive reactance is relatively increased, so it is necessary to use a polar electrolytic capacitor. Because of the electrolyte inside, the capacity can be made large, allowing low-frequency alternating current to pass. However, because of the organic medium between the internal two poles, the withstand voltage is limited. Non-polar capacitor is mostly used in circuits such as low-frequency AC paths, filtering, decoupling, and bypassing. (low-pass) 7) In a battery-powered circuit, why does the capacitor charging and discharging have the delay effect?Capacitors accumulate electric charge. During the charging process, the voltage rises slowly, while discharging vice versa. During charging, at the beginning, the voltage across the capacitor is zero, as the time goes by, the voltage gradually rises to the voltage you set to control the switching of the circuit. Of course, the discharging process can also be used to achieve this. The delay time is related to capacitor capacity, capacitor leakage, charging resistance, voltage, and sometimes the load resistance is also taken into consideration. 8) The resistance-capacitance coupling amplifier circuit can only amplify AC signals, but cannot amplify DC signals?Capacitor is an electronic component that blocks DC and AC. Therefore, the resistance-capacitance coupling amplifier circuit can only amplify AC signals. A direct coupling amplifier circuit is used to amplify DC signals. 9) How to tell the coupling capacitor and the bypass capacitor in the amplifying circuit?The negative pole of the coupling capacitor is not grounded, but is connected to the input of the next stage, and the negative pole of the bypass capacitor is grounded. 10) How to choose coupling capacitor for the multi-stage AC amplifier circuit?Generally ceramic capacitors can be done, and tantalum capacitors can be used if the performance is good. According to the frequency range of your input signal, capacitance of 103,104 can be used for high frequencies, and also electrolytic capacitors of about 22uF can be used for lower frequency AC signals. 11) The amplifying circuit adopts direct coupling, and the feedback network is a pure resistor network. Why is the circuit only possible to produce high-frequency oscillation?The oscillation comes from the phase shift of the closed loop reaching 180 degrees and the loop gain at this time is greater than zero. Using a pure resistor network as a feedback network will definitely not have phase shift, which comes from the open loop circuit of the amplifier only. Using a direct-coupled open-loop amplifier, there will be no capacitive elements between stages that will cause phase shifts, but the capacitor inside the transistor or MOS tube will cause it. These capacitances are all fF, the maximum is pF. The resonant frequency of the circuit composed of these capacitors and the equivalent resistance of the circuit is quite high. Therefore, the amplifier adopts direct coupling, with a pure resistor feedback network, which can only produce high-frequency oscillations. 12) How to estimate the output resistance of the first-stage amplifier and the input resistance of the second-stage amplifier? When the amplitude of the signal source is too large, what will happen at the output of the two-stage amplifier? Shake the input end of the amplifier and observe the output end to see what appears? why?A. The input resistance of the second stage amplifier is the output resistance of the first stage amplifier. B. Have distortion. C. Cause clutter due to human body induction. 13) How to use the charge and discharge of capacitors to understand filtering, decoupling and bypassing?Capacitors block DC and pass AC. Blocking DC is easy to understand, but passing AC is not easy to understand. As long as you understand it, you can understand filtering, decoupling and bypass.Capacitors are charging and discharging, but the direction of alternating current changes alternately. The magnitude of the amplitude also changes periodically. The entire changing image is a sine curve.The capacitor is connected to the AC circuit, and due to the periodic change of the AC voltage, it is also periodically changes. There is a charging and discharging current in the line. This charging and discharging current has the same shape as the voltage except that the phase is 90 degrees ahead of the voltage, which is equivalent to the AC passing through the capacitor.The alternating current passing through the resistance consumes electric energy (heating) on the resistor. However, the capacitor only exchanges energy with the power supply. The power supply sends energy to the capacitor when charging, and the capacitor returns the electrical energy to the power supply when discharging. Therefore, the power generated by multiplying the voltage by the current here is called reactive power.What needs to be clear is that when the capacitor is connected to an AC circuit, the flowing electrons (current) do not really rush through the insulating layer, but generate current in the circuit. This is because in the circuit, reverse discharge and forward charge are in the same direction, the forward discharge and reverse charge either. Understand that the capacitor is connected to AC, then the AC component is bypassed to the ground, and also the filtering is completed. 14) How to use bypass capacitor, filter capacitor and decoupling capacitor respectively?These three types of capacitors are actually used for filtering, but they are used in different circuits, so their names and usages are different.Filter capacitor, this is the capacitor we usually use after power rectification. It is a capacitor that rectifies the AC of the rectifier circuit into a pulsating DC and smoothes it by charging and discharging. This type of capacitor is generally an electrolytic capacitor with a large capacity.Bypass capacitors are used to filter out the high frequency components in the input signal. They are mainly used to filter high frequency clutter. Usually, ceramic capacitors and polyester capacitors are used. The capacity is small and is at the picofarad level.The decoupling capacitor takes the interference of the output signal as the filtering object. It is equivalent to the battery and uses its charge and discharge so that the amplified signal will not be interfered by the sudden change of the current. Its capacity depends on the frequency of the signal and the degree of ripple suppression. 15) Regarding the function of the capacitor, under what circumstances use the coupling capacitor and under what circumstances use the filtering capacitor?After the alternating voltage is applied to the two ends of the capacitor, it will continue to charge and discharge with the alternating frequency of the current. At this time, there is an alternating current of the same frequency in the circuit, which is the passing characteristic of the capacitor.When the frequency is appropriate, the capacitor can be regarded as a path to the circuit, and the AC output of the previous stage can be transmitted to the subsequent circuit through the capacitor.For direct current, it is isolated, because when the voltage at both ends is charged to be equal to the circuit voltage, there will be no more charging current.When acting on the transmission of front and rear AC signals, it is coupling, and when acting on filtering out fluctuation components and useless AC components, it is filtering. 16) The capacitor filter of the rectifier circuit uses its charge and discharge, but sometimes the filter uses the capacitor to have a different capacitive reactance to the non-pass frequency signal, such as a bypass capacitor. So which point is used when analyzing capacitor filtering?The theoretical explanation of using capacitor characteristic is more general, and the theory using capacitive reactance is more in-depth. The role of capacitor is to use its charge and discharge characteristics, depending on what components you want to filter out. Use large capacitors to filter low frequencies and a small capacitor for high frequency. In theory, the filtering in the low-frequency rectifier circuit and the bypassing in the high-frequency circuit are the same, and the difference is the capacitive reactance. 17) After the filter capacitor is fully charged, it will discharge the back circuit and then in cycle?Such a working process in the circuit, capacitor is related to the frequency of the signal. First of all, it depends on what you want to put the capacitor in the circuit. When used as a filter, it filters out a certain frequency signal to the ground. For example, the capacitors at the front end of the chip power supply are decoupling. The phenomenon you mentioned is like the filter capacitor before the voltage regulator is turned off and the filter capacitor of the switching power supply. 18) What is the specific coupling of capacitors? Is there any difference compared with filtering?Coupling refers to the process of signal transmission from the first stage to the second stage, and usually refers to AC coupling when it is not specified. Decoupling refers to taking further filtering measures on the power supply to remove the influence of mutual interference between the two levels of signals through the power supply. The coupling constant refers to the time constant corresponding to the product of the coupling capacitance value and the second-stage input impedance value.Decoupling has three purposes: D.Remove the high-frequency ripple in the power supply, and cut off the high-frequency signal of the multi-stage amplifier through the crosstalk path of the power supply.E.When the large signal is working, the circuit's demand for the power supply increases, causing the power supply fluctuations, here decoupling reduces the impact of power fluctuations on the input stage/high voltage gain stage during large signals.F. Form a floating ground or floating power supply, and complete the coordination of various parts of the ground or power supply in a complex system.The high-frequency switching noise generated by the active device during switching will propagate along the power line. The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the noise on the board and to guide it to the ground. 19) How to distinguish whether the capacitor in the circuit is a filter capacitor or a bypass capacitor?The filter capacitor is in the power circuit; the bypass capacitor is in the signal circuit.In fact, their function is basically the same. The filter capacitor: Bypasses or filters out the pulsating current components and plays the role of charging and discharging. Bypass capacitor: Filter or bypass high frequency or low frequency components in the circuit. 20) Is the coupling capacitor a decoupling capacitor?It is completely different. The coupling capacitor is for signal transmission, and the decoupling capacitor is for reducing interference.

Introduction A Capacitor is a component that can store and release electricity, and it is also one of the most commonly used electronic components. Its distinguishing feature is the "Pass Alternating Current (AC), Stop Direct Current(DC)". In a DC circuit, a capacitor is equivalent to an open circuit. Based on this, we will have this question: What the differences betwen ac and dc capacitors? or Are ac and dc capacitors interchangeable? What's the difference between batteries and capacitors? or Why can't we use capacitors instead of batteries? As for capacitor calculations, what the time constant for discharging a capacitor? Here you will get the answers. Figure 1. Capacitor Symbol Catalog Introduction Ⅰ Why Can the Battery (DC) Charge the Capacitors? Ⅱ DC Capacitors vs AC Capacitors Ⅲ Battery or Capacitor? Ⅳ Calculate the Time Constant for the Discharge of the Capacitors? Ⅴ FAQ Ⅰ Why Can the Battery (DC) Charge the Capacitors? In circuit analysis, there are two types of circuit responses: zero-input response and zero-state response. The so-called zero input response means that the input signal is zero; the so-called zero-state response means that the states of all energy storage components and various power supplies in the circuit are zero.When analyzing the zero-state response, short-circuit the voltage source and open the current source. For the capacitor, at the moment of energization in the zero state response, it can be considered as a voltage source with zero voltage, so it is equivalent to a short circuit. Analyze the following figures: Figure one is the circuit structure: power supply E, internal resistance r, switch QF, capacitor C and resistance R. When the switch QF is turned on, let's take a look at the current Ic and voltage Uc flowing through the capacitor: Figure 2. Zero-input Response and Zero-state Response Curve We see that at the moment t=0, the current flowing through the capacitor is the largest. The capacitor at this time is equivalent to a voltage source with zero voltage, and the power source E must be charged to it through the internal resistance r. Therefore, we can understand that it is actually a short circuit, so the maximum charging current, that is, the charging current Icmax at t=0 is: . In the figure, we can see that after 5τ, the current has been zero and the voltage has been charged to almost E. After that, the current flowing through the capacitor will not change any more, and the capacitor at this time plays a role in isolating the direct current. As can be seen in the figure, the charging process of the capacitor is divided into two parts, one is the transient transition process, and the other is the steady state process.Next, analyze the transition process carefully. Let us first look at the opportunity RC of the resistance r and the capacitance C. Resistance is equal to voltage divided by current, and capacitance is equal to electricity divided by voltage, and electricity is equal to current divided by time, so there is: , here T is called the time constant, generally represented by τ.The current thus flowing through the capacitor is: The exponential function here, its exponent is equal to the ratio of time to the time constant, so it is a pure number. When the time is equal to 0, Ic=Icmax; when the time is equal to 5τ, the value of the exponential function is 6.738×10-3. After substituting the above formula, get the current at this time is: At this time, the expression of the capacitor voltage Uc is: Note: Theoretically, the voltage on the capacitor should be charged to ER/(R+r), but because in the steady state, the impedance of the capacitor is infinite, so its voltage can be charged to E.From here we can see that the so-called capacitor blocking DC actually refers to its steady-state characteristics. In the steady state, the equivalent impedance of the capacitor is infinite, and the DC current cannot pass through it, so the current is zero, and there is a very small leakage current at most. In the transient state, the capacitor can flow current, and in the initial stage since the current is similar to a voltage source due to the capacitance, its characteristic is almost a short circuit, so the initial value of the current is the maximum. If our power source is not a battery, but a square wave pulser, what is the voltage of the resistor R after the capacitor? Figure 3. Square Wave Pulser The Figure 3. is a case where the time constant is small, which reflects the impulse response of the capacitor; and the picture below is a case where the time constant is large, which reflects these two effects have a large number of applications. If our power supply is AC, what is the voltage on the resistor R after the capacitor?When discussing the response of the capacitor to the AC current range, we need to temporarily look back at the first picture. From the figure, we can see that when the current takes the maximum value, the voltage is the minimum value, however, when the current takes the minimum value, the voltage is the maximum value. Why is that?The capacitance is equal to the ratio of the electric quantity to the voltage, that is, C=Q/U=It/U, from which the current is obtained: I=CU/t. And the voltage Uc on the capacitor is actually constantly changing. It is a function of time, so the above formula can be written as: This formula is very important, it is the key to unlock the capacitor under the action of AC power.The AC voltage can be expressed as, put it into the expression of the capacitor current , and get: We can see that when the voltage is zero, the current has reached its maximum value. In other words, for an AC power supply, the current I flowing through the capacitor leads the voltage by 90 degrees. It reveals the expression form of capacitance under AC voltage.Capacitors are used to block direct current, but they only have this performance in steady state. When the DC power supply changes rapidly, that is, the power supply continuously changes from zero to the maximum value, and becomes zero again. In this cycle, we can see that the capacitor not only does not block the DC, but becomes a component with almost zero impedance.In fact, it can be known from the capacitive reactance () that when the frequency of the power supply increases, the capacitive reactance of the capacitor decreases linearly with the increase in frequency. When we charge the capacitor with a DC power supply enough, the charging voltage of the capacitor can reach the same level as the electromotive force of the power supply. Here the key is that the capacitor is an energy storage element. Figure 4. Various Capacitors Ⅱ DC Capacitors vs AC Capacitors 1) Whether DC capacitors and AC capacitors are polarized: AC capacitors are also called non-polarized capacitors. As can be seen from the literal meaning, it can be polarity-independent. So it can be used in AC and DC circuits. The DC current uses a polarized capacitor, which has a high capacity, and a relatively small withstand voltage. In addition, both of them will be lost over time.2) The mobility of DC capacitors and AC capacitors are different: the voltage at one end of the DC capacitor is always high, and the current will always be the same and flow in one direction. While the two lines from the AC capacitor power supply, their voltage level is changing, so that the current can flow from A to B, or from B to A, and make certain adjustments and changes over time.3) Direct current and alternating current are different in direction conversion: alternating current can be regarded as two groups of direct current in turn to exert an effect on the load, which can be understood as the vector sum of the two groups of direct current in different time periods. The alternating current can be understood as a group of direct current in one direction in a short enough time. Figure 5. Ceramic Capacitors Ⅲ Battery or Capacitor? Capacitors and batteries are both electrical components, and both are energy storage components. But battery and capacitor are two completely different concepts. The difference between them is:1) Chemical Energy vs Electrical EnergyThe battery stores chemical energy, and then converts it into electrical energy to output. Capacitors store electrical energy, which depends on the two plates to determine the capacity. The former is a chemical change, the latter is a physical change. The main physical feature of a capacitor is to store electric charge, which can be charged and discharged like a battery, but does not undergo a chemical reaction.2) CapacityBatteries store a lot of electrical energy, but capacitors store less.3) Charge and Discharge Figure 6. Charge and Discharge Curve The charging and discharging speed and the number of times are different. Generally, it only takes a few seconds or minutes to charge a capacitor, while a battery usually takes several hours. The number of charging and discharging of the capacitor is at least tens of hundreds to thousands of millions of times, and the battery is generally only a few hundred to a thousand times.4) FunctionsThe purpose of the two is different. Capacitors can be used for coupling, blocking, filtering, phase shifting, RC, LC resonance and as energy storage components for instantaneous large current discharge. The battery is only used as a power source. Replacing Bike Battery with Capacitor Ⅳ Calculate the Time Constant for the Discharge of the Capacitors? Let’s review the calculation formula for the charge and discharge time of the capacitor. Suppose there is a power supply that charges the capacitor C through the resistor R, V0 is the initial voltage value on the capacitor, Vu is the voltage value after the capacitor is fully charged, and Vt is the voltage value at any time t On the capacitor, then the following calculation formula can be obtained:Vt = V0 + (Vu – V0) * [1 – exp( -t/RC)]If the initial voltage on the capacitor is 0, the formula can be simplified to:Vt = Vu * [1 – exp( -t/RC)]...Charging formulaIt can be seen from the above formula that because the index value can only be infinitely close to 0, but it will never be equal to 0, it takes infinite time for the capacitor to be fully charged.🔺When t = RC, Vt = 0.63Vu🔺When t = 2RC, Vt = 0.86Vu🔺When t = 3RC, Vt = 0.95Vu🔺When t = 4RC, Vt = 0.98Vu🔺When t = 5RC, Vt = 0.99VuIt can be seen that after 3~5 RCs, the charging process is basically over. When the capacitor is fully charged, the power supply is short-circuited, and the capacitor C will be discharged through R. At any time t, the voltage on the capacitor is:Vt = Vu * exp( -t/RC)...Discharging formula   Ⅴ FAQ 1. Can you use a capacitor as a battery?A voltage applied across the conductors creates an electrical field in the capacitor, which stores energy. A capacitor operates like a battery in that, if a potential difference is applied across it that can cause a charge greater than its "present" charge, it will be charged up.   2. Why can't we use capacitors instead of batteries?Capacitors don't provide large amount of energy because they have less energy density than batteries. Capacitors are useful to provide short duration power requirements because they can be charged or discharged at a higher rate than the batteries.   3. What is the difference between a battery and supercapacitor?Differences Between Capacitor and BatteryBatteries excel at storing energy, while supercapacitors rate better for power. In practical terms, this means that supercapacitors are better at discharging their stored energy quickly, while batteries save more energy in the same amount of material.   4. Which is better battery or capacitor?A capacitor is able to discharge and charge faster than a battery because of this energy storage method also. ... However, in general batteries provide higher energy density for storage, while capacitors have more rapid charge and discharge capabilities (greater Power density).   5. What is discharging of capacitor?Discharging a capacitor means releasing the charge stored within the capacitor. ... Hence the capacitor current exponentially reaches zero from its initial value, and the capacitor voltage reaches exponentially to zero from its initial value during discharging.   6. Is it safe to discharge a capacitor with a screwdriver?It's often safe to discharge a capacitor using a common insulated screwdriver; however, it is usually a good idea to put together a capacitor discharge tool and use that for electronics with larger capacitors such as household appliances.   7. Can you discharge a capacitor with a multimeter?The multimeter isn't used directly to discharge the stored energy of a capacitor. Instead, people use it to measure the voltage and power of the capacitor to know whether it is fully released or not. You can use different tools such as a light bulb or a DIY discharge tool for the process.   8. Why do we need to discharge a capacitor?You must discharge the capacitors before working on power supply circuits so you won't get shocked. ... Using a screwdriver to discharge the capacitor is not recommended because you can generate a spark and damage the printed circuit board or circuitry of the power supply. You can even blow the power section.   9. What is discharging time of capacitor?RC Discharging Table. Note that as the decaying curve for a RC discharging circuit is exponential, for all practical purposes, after five time constants the voltage across the capacitor's plates is much less than 1% of its inital starting value, so the capacitor is considered to be fully discharged.   10. What is the time constant of a capacitor?The time constant of a series RC (resis-tor/capacitor) circuit is a time interval that equals the product of the resistance in ohms and the capacitance in farad and is symbolized by the greek letter tau (τ). The time in the formula is that required to charge to 63% of the voltage of the source.   11. Is the time constant the same for charging and discharging the capacitor?The time constant of a resistor-capacitor series combination is defined as the time it takes for the capacitor to deplete 36.8% (for a discharging circuit) of its charge or the time it takes to reach 63.2% (for a charging circuit) of its maximum charge capacity given that it has no initial charge.   12. What is the formula of discharging of capacitor?q=ϵC(1−eCR−t) where q is the charge on the capacitor at time t,CR is called the time constant, ϵ is the emf of the battery. Discharging: If the plates of a charged capacitor are connected through a conducting wire, the capacitor gets discharged.   13. What is energy stored in capacitor?Electrical potential energyEnergy stored in a capacitor is electrical potential energy, and it is thus related to the charge Q and voltage V on the capacitor. We must be careful when applying the equation for electrical potential energy ΔPE = qΔV to a capacitor. Remember that ΔPE is the potential energy of a charge q going through a voltage ΔV.   14. Where is energy stored in capacitor?A charged capacitor stores energy in the electrical field between its plates. As the capacitor is being charged, the electrical field builds up. When a charged capacitor is disconnected from a battery, its energy remains in the field in the space between its plates.   15. Which type of current is blocked by a capacitor?Alternating current doesn't really "flow", it just oscillates back and forth. A capacitor acts like an elastic membrane, it allows the oscillation but blocs the flow of DC current.

Introduction As a passive device, Capacitors have unique functions in electronic circuits such as tuning, bypassing, coupling, and filtering. For example, it is used in the tuning circuit of the transistor radio, and also used in the coupling circuit and bypass circuit of the color TV. With the rapid development of electronic information technology, the update speed of digital electronic products is getting faster and faster. Capacitors play an important role in consumer electronic products such as flat-panel TVs (LCD and PDP), notebook computers, digital cameras and other products. Therefore, it is very important to ensure the capacitances and test its quality. Here this article will talk about how to test/check a capacitor in detail. 3 Ways to Check Capacitors in Circuit with Meters & Testers Catalog Introduction Ⅰ Test a Capacitor Using Multimeter 1.1 Digital Multimeter Use 1.2 Capacitor Measurements Matter 1.3 Test Non-polar Capacitors 1.4 Test Polar Capacitors 1.5 Test Chip Capacitors 1.6 Test Solid State Capacitors 1.7 Test Electrolytic Capacitors 1.8 Test Variable Capacitors 1.9 Capacitor Polarity Distinction Ⅱ Test a Capacitor Using Bridge Ⅲ Test a Capacitor Using Professional Equipment Ⅳ FAQ Ⅰ Test a Capacitor Using Multimeter 1.1 Digital Multimeter Use 1.1.1 Using Capacitance GearSome digital multimeters have the function of measuring capacitance, and their ranges include five ranges: 2000p, 20n, 200n, 2μ and 20μ. During test, the two pins of the discharged capacitor can be directly inserted into the Cx jack on the meter board, and the display data can be read after selecting the appropriate range.🔺2000p range is suitable for measuring capacitances less than 2000pF.🔺20n range is suitable for measuring capacitances between 2000pF and 20nF.🔺200n range is suitable for measuring capacitances between 20nF and 200nF.🔺2μ range is suitable for measuring capacitances between 200nF and 2μF.🔺20μ gear is suitable for measuring the capacitance between 2μF and 20μF. Experiments have proved that some types of digital multimeters have large errors when measuring small capacitors below 50pF, and there is almost no reference value for measuring capacitors below 20pF. At this time, the series method can be used to measure small-value capacitors. For example: measure a capacitor of about 220pF. Test its actual capacity C1 with a digital multimeter, and then connect the small capacitor in parallel to measure its total capacity C2, then the difference between the two (C1-C2) is the capacity of the small capacitor. It is very accurate to use this method to measure small capacitance of 1-20pF. 1.1.2 Using Resistance GearIn practice, it has proved that the charging process of the capacitor can also be observed with a digital multimeter, which is actually a discrete digital quantity that reflects the change of the charging voltage. Assuming that the measurement rate of the digital multimeter is n times/second, in the process of observing the charging of the capacitor, n independent and successively increasing readings can be seen every second. According to this display values, the quality of the capacitor can be detected and the size of the capacitance can be estimated. This method is suitable for measuring large-capacity capacitors from 0.1μF to several thousand microfarads. 1.1.3 Using Voltage GearUsing a digital multimeter to detect capacitors with DC voltage is actually an indirect method. This method can measure small-capacity capacitors from 220pF to 1μF, and can accurately measure the size of the capacitor's leakage current. 1.1.4 Using BuzzerUsing the buzzer of the digital multimeter, you can quickly check the quality of the electrolytic capacitor. For example, set the digital multimeter to the buzzer position, and use two test leads to contact the two pins of the capacitor Cx to be tested. A short buzzer should be heard, then the sound stops, and the overflow symbol "1" is displayed at the same time. Then, exchange the two test leads for another measurement, the buzzer should sound again, and finally the overflow symbol "1" is displayed. This situation indicates that the measured electrolytic capacitor is basically normal. At this point, you can dial to 20MΩ or 200MΩ to measure the leakage resistance of the capacitor to judge whether it is good or bad. Figure 1. Various Capacitor Stuff 1.2 Capacitor Measurements Matter (1) Before the measurement, the two pins of the capacitor should be short-circuited and discharged, otherwise the reading process may not be observed.(2) Do not touch the capacitor electrode with two hands during the measurement process, so as to prevent the meter from jumping.(3) During the measurement process, the value of Vin(t) changes exponentially, and it drops quickly at the beginning. As time goes by, the speed of decline will become slower and slower. When the capacity of the capacitor Cx under test is less than several thousand picofarads, and the measurement rate of the meter is low, it is too late to reflect the initial voltage value, so the initial display value of the meter is lower than the battery voltage at very first.(4) When the measured capacitance value is greater than 1μF, in order to shorten the test time, the resistance gear can be used. In addition, when the capacity of the capacitor under test is less than 200pF, it is difficult to observe the charging process because the change in readings is very short.Be sure to cut off the power and discharge capacitor before measuring. The method of discharging is to find a metal object such as a screwdriver, hold the exposed part of the metal on the insulating handle with the two pins, and measure the capacitance with a digital multimeter. Locate the capacitor block and then plug the two pins into the socket for capacitance measurement, and wait for the changing reading on the meter screen to stabilize. The actual value is the capacitance of the capacitor on the side. If has leakage, an analog multimeter can be used. When measuring, the small-capacity capacitor multimeter can be placed in RX1K or RX100. The two test leads are connected to the capacitor, the pointer deflects clockwise, and then as the capacitor is fully charged, there is no current flows, finally the watch hand will reappear counterclockwise and return to infinity. The larger the angle of the watch hand, the greater the capacity. During the deflection process, the pointer must swing at a constant speed so that it can return to infinity, which preliminarily shows that the capacitor has no leakage.If the needle suddenly slows down or does not return at a certain position on the dial, it means that the capacitor is leaking in a certain period. If it is displayed as infinity at the end, it shows that there is no leakage, but this can only be a rough judgment. If you want to find an accurate value, you have to use a capacitance meter. And the observation characteristic on the capacitance leakage tester or oscilloscope, this is impossible for ordinary people to have. There are also capacitors that have withstand voltage, which is generally written on their body. However, some ceramic capacitors are not marked on it, be careful when selecting them. Figure 2. Film Capacitor (cbb21) 1.3 Test Non-polar CapacitorsIf it is a non-polar capacitor, the multimeter can be adjusted to the "diode" gear to measure the on-off state. If the multimeter displays "1", it is normal; if displays "0" or other numbers, it means the capacitor is damaged. 1.4 Test Polar CapacitorsElectrolytic capacitors with polarities have "bulging", "deformation" or "leakage" in the shell, which show they are damaged. The capacitance block of a digital multimeter can also be used to measure the quality of the capacitor:(1) According to the rated capacitance marked by the capacitor, set the multimeter to the appropriate block.(2) Insert the capacitor into the hole of the multimeter to measure the capacity.If the capacitance is within the rated value range, it means the capacitor is intact, otherwise the capacitor is damaged. 1.5 Test Chip Capacitors1) Adjust the multimeter to the appropriate ohm gear. The principle of gear selection is: 1μF capacitor uses 20K gear, 1~100μF capacitor uses 2K gear, and larger than 100μF uses 200 gear.2) Determine the polarity. First adjust the multimeter to 100 or 1K ohms. Assuming that one pole is positive, connect the black test lead to it, and the red test lead to the other pole. Note the resistance value, and then discharge the capacitor. Then change the test lead to measure the resistance. The black test lead with a large resistance value is connected to the positive electrode of the capacitor.3) Then connect the red pen of the multimeter to the positive electrode of the capacitor, and the black pen to the negative electrode of the capacitor. If the display gradually increases from 0, and the overflow symbol 1 is displayed at the end, which shows the capacitor is normal. If it is always displayed as 0, the capacitor is short-circuited. If 1 is displayed, the internal circuit of the capacitor is open. Figure 3. Chip Capacitors 1.6 Test Solid State Capacitors✔️Capacitance Greater than 20μFWith a common digital multimeter, the maximum measured value of the capacitance block is 20μF, which sometimes cannot meet the test requirements. To this end, the following simple method can be used to measure capacitance greater than 20μF, and also the maximum capacitance of several thousand microfarads can be measured. When using this method to measure large-capacity capacitors, there is no need to make any changes to the original circuit of the digital multimeter.The measurement principle of this method is based on the formula C = C1C2/(C1+C2) in series with two capacitors. Since two capacitors with different capacities are connected in series, the total capacity after series connection is smaller than the smaller capacitor. Therefore, if the capacity of the capacitor under test exceeds 20μF, only one capacitor with a capacity less than 20μF should be used. In series with it, it can be directly measured on the digital multimeter. According to the formula above mentioned, it is easy to deduce C1=C2C/(C2-C), using this formula can calculate the capacitance value of the capacitor under test. ✔️Capacitance Less than 10μFBecause the capacity of a fixed capacitor below 10pF is too small, it can only be roughly checked for leakage, internal short circuit or voltage breakdown with a multimeter. When measuring, you can choose the R×10k block, and use two test pens to connect the two pins of the capacitor arbitrarily, and the resistance should be infinite. If the measured resistance value (the pointer swings to the right) is zero, it means that the capacitor is damaged by leakage or has internal breakdown. ✔️Capacitance between 10PF and 0.01μFDetect whether the capacitor is charging, and then judge whether it is good or bad. The multimeter selects the R×1k block. The β value of the two transistors is above 100, and the penetration current should be small. A composite tube can be used consist of silicon transistors. The red and black test leads of the multimeter are respectively connected to the emitter e and collector c of the composite tube. Due to the amplification effect of the composite triode, the charge and discharge process of the capacitor under test is amplified, and the amplitude of the pointer of the multimeter is enlarged, which is convenient for observation. It should be noted that during the test operation, especially when measuring small-capacity capacitors, it is necessary to repeatedly exchange the contact points A and B of the tested capacitor pin to clearly see the swing of the meter pointer. ✔️Fixed Capacitance of 0.01μFFor a fixed capacitance above 0.01μF, the R×10k block of a multimeter can be used to directly test whether the capacitor has the charging process and internal short circuit or leakage, in addition, the capacitance of the capacitor can be estimated according to the magnitude of the pointer swing to the right. Figure 4. Electrolytic Capacitors 1.7 Test Electrolytic Capacitors1) Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, ranges should be selected for different capacities when measuring. According to experience, in general, the capacitance between 1 and 47μF can be measured with the R×1k block, and the capacitance larger than 47μF can be measured with the R×100 block.2) Connect the red test lead of the multimeter to the negative pole and the black test lead to the positive pole. At the moment of contact, the pointer of the multimeter will deflect to the right by a greater degree (for the same electrical barrier, the greater the capacity, the greater the swing), and then gradually turn to the left Turn around until it stops at a certain position. The resistance value at this time is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than several hundred kΩ, otherwise, it will not work normally. In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the hand does not move, it means that the capacity has disappeared or the internal circuit is broken; if the measured resistance value is very small or zero, it means that the capacitor has a large leakage or has been broken down.3) For electrolytic capacitors with unknown positive and negative signs, the above method of measuring leakage resistance can be used to distinguish. That is to measure the leakage resistance arbitrarily, remember its size, and then exchange the test leads to measure a resistance value. The larger resistance of the two measurements is the positive connection, that is, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode. Use a multimeter to block electricity and charge the electrolytic capacitor. According to the magnitude of the pointer swing to the right, the capacity of the electrolytic capacitor can be estimated.When measuring electrolytic capacitors, if the measured value does not change significantly, the corresponding pins of the probe should be exchanged for multiple measurements. 1.8 Test Variable Capacitors1) Rotate the shaft gently and smoothly. When pushing the load shaft in full directions, there should be no looseness of it.2) Rotate the shaft with one hand and gently touch the outer edge of the film set with the other hand. You should not feel any looseness. The variable capacitor with poor contact between the rotating shaft and the moving plate can no longer be used.3) Place the multimeter in the R×10k gear, connect the two test leads to the moving piece and the lead end of the fixed piece of the variable capacitor with one hand, and slowly rotate the shaft several times back and forth with the other hand. The pointers of the multimeter should not move at infinity. In the process of rotating the shaft, if the pointer sometimes points to zero, it indicates that there is a short-circuit point between the moving piece and the fixed piece. If it encounters a certain angle, the multimeter reading is not infinity but a certain resistance value, indicating that the variable capacitor has a leakage phenomenon between the film and the stator. 1.9 Capacitor Polarity DistinctionThe black part with a mark on the capacitor is negative. There are two semicircles on the position of the capacitor on the PCB, and the pin corresponding to the colored semicircle is the negative electrode. The length of the pins is also useful to distinguish the polarity: the long pin is anode and the short pin is cathode.When we don't know the positive and negative poles of the capacitor, we can use a multimeter to figure them out. The medium between the two poles of the capacitor is not an absolute insulator, and its resistance is not infinite, but a finite value, generally above 1000 megohms. The resistance between the two poles of a capacitor is called insulation resistance or leakage resistance. Only when the positive electrode of the electrolytic capacitor is connected to the positive power supply (the black test lead), and the negative terminal is connected to the negative power supply (the red test lead), the leakage current is small (the leakage resistance is large), on the contrary, the leakage current increases (the leakage resistance decreases).Without knowing it, you can first assume the “+” pole of a certain pole. Using R*100 or R*1K of the multimeter, connect the test leads, and record the scale of the stop of the test needle (the resistance value of the test needle to the left is large), and the reading can be read directly for a digital multimeter. Then discharge the capacitor, then exchange the two test leads, and perform the measurement again. In the two measurements, the black test lead is connected to the positive electrode of the electrolytic capacitor when the last position of the needle is to the left (or the end with large resistance).When measuring large capacity capacitors, if you need to measure the positive and negative back and forth, discharge it to avoid damage to the multimeter. In addition, in high-frequency circuits, switching power supply circuits have many small capacitors, which ordinary multimeters cannot correctly judge whether they are good or bad. In terms of this case, it is recommended to use a dedicated digital capacitance meter to measure. Figure 5. SMD Capacitor Ⅱ Test a Capacitor Using BridgeThe data measured with a multimeter is not too accurate, and it can only measure the deviation of the capacity. For a little professional, you can use a bridge. When testing a capacitor with a digital bridge, you can clamp the lead of the capacitor to test its capacity, which can also show the loss of the capacitor, especially through the loss, it is easier to distinguish the quality of the capacitor.   Ⅲ Test a Capacitor Using Professional EquipmentIn general, capacitors have special test equipment for each performance, such as capacitor durability test, destructive test, loss angle test, inter-electrode withstand voltage test, self-healing test, charge and discharge test, pulse voltage test, spontaneous combustion test, ripple current durability test, etc., but for most users, these devices are more expensive and difficult to operate. If you really want these data, you can entrust a third party to test or ask the manufacturer for relevant information.   Ⅳ FAQ1. How do you check if a capacitor is bad?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 tell 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.   3. What are the symptoms of a bad start capacitor?Start Capacitor FailureMotor 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.   4. Can a capacitor test good and still be bad?It can, and most often does, although it is probably lower in capacitance than it originally was, but still usually within tolerance. There isn't likely to be a problem with leakage. There are two ways to test an ESR meter, a circuit unpowered or an oscilloscope.   5. How long can a capacitor last?Age. Like all things, capacitors have a limited life span. Most are designed to last approximately 20 years, but a number of factors can cause them to wear out more quickly.   6. 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 capacitors value and the third digit indicates the number of zero's to be added.   7. Will a capacitor discharge on its own?Will a Capacitor Discharge On Its Own? In theory, a capacitor will gradually lose its charge. A fully charged capacitor in an ideal condition, when disconnected, discharges to 63% of its voltage after a single time constant. Thus, this capacitor will discharge up to near 0% after 5 time constants.   8. How do I know if my AC capacitor is bad?The most common signs and symptoms of a bad AC capacitor include:AC not blowing cold air.AC takes a while to start once you turn it on.Humming sound coming from your air conditioner.AC shuts off on its own.AC won't turn on.   9. What side of capacitor is positive?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.   10. Can I use a multimeter to discharge a capacitor?The multimeter isn't used directly to discharge the stored energy of a capacitor. Instead, people use it to measure the voltage and power of the capacitor to know whether it is fully released or not. You can use different tools such as a light bulb or a DIY discharge tool for the process.   11. How fast can a capacitor discharge?A fully charged capacitor discharges to 63% of its voltage after one time period. After 5 time periods, a capacitor discharges up to near 0% of all the voltage that it once had.   12. Can a bad capacitor ruin a compressor?Using the wrong capacitor rating or a poor quality capacitor can adversely affect the operation of the motor, the compressor or an entire HVAC system. ... Depending on the motor load, this may result in a reduction in the motor's overall speed.   13. Can I replace a start capacitor with a run capacitor?Run Capacitors. 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 not handle current continuously.   14. How do you check 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. And so you can somewhat assume that your capacitor is in good condition.   15. What if a capacitor reads high?The high resistance across the capacitor is a sign that the capacitor is faulty. It is reading as if there is an open circuit.   16. How many ohms should a capacitor have?Make sure the capacitor is fully discharged. Set the meter on the Ohmic range (Set it at least on 1000 Ohm = 1kΩ). Connect the multimeter probes to the capacitor terminals (Negative to Negative and Positive to Positive).   17. What if a capacitor reads low?If it reads lower than nominal value, you may want to replace it. Non-polar capacitors lower than 1μF should not alter that much with aging. Capacitors in frequency sensitive circuits such as filters, time delays, should have a tighter tolerance.   18. What happens when capacitor goes bad?A bad capacitor prevents the exterior unit from properly functioning, which hinders the cooling process as a whole. Second, improper voltage delivery to exterior unit components forces the system to work harder as it attempts to perform its job. Additional components often sustain damage due to a faulty capacitor.   19. How can you tell if a capacitor is bad?Symptoms of defective capacitors may include:Excessive noise in audio or video, including 60hz audio hum or rolling bars in video.Scratchy, distorted, or missing audio.Low contrast, blurry, or distorted LCD displays.Intermittent or outright failure.   20. What does a damaged capacitor look like?A busted capacitor can be obviously broken (leaking brownish fluid, corroded, or with the leads severed), but sometimes it's subtle. The top of a blown capacitor will be slightly bent outwards in a convex shape, rather than flat or slightly indented inwards like a working capacitor.

What is a capacitor? Capacitor, a electronic component to hold charges, represented by the letter C. It composes of two metal electrodes between a layer of insulating dielectric. When a voltage is applied between the two metal electrodes, the charge is stored on the electrode, so the capacitor is an energy storage electrical part. Any of two conductors that are insulated and close to each other form a capacitor. In addition, the parallel plate capacitor consists of the electrode plate and the dielectric of the capacitor.  Capacitor is one of the widely used electronic components in electronic equipment. It is widely used in stopping DC and alternating AC, coupling, bypass, filtering, tuning loop, energy conversion, control and so on. Capacitor is different from capacitance. The capacitance is the basic physical quantity, the symbol C, the unit is F (Farah).   A video introducing basic knowledge of capacitors Catalog   I. Capacitor characteristics II. Functions of capacitor in electrical circuits III. How to use capacitors? IV. Capacitor types V. Capacitor volume VI. Charge and discharge of a capacitor VII. Matters needing attention when using capacitors VIII. Common fault of capacitor and treatment method FAQ   I. Capacitor characteristics  - It has the ability of charge and discharge, preventing DC current from passing through, allowing AC current to pass through.  - During the charge and discharge process, the charge on the bipolar plate accumulates, that is, the voltage is set up, therefore, the voltage on the capacitor will not change abruptly. Charging: two plates with the same amount of dissimilar charge, each plate with the absolute value of the charge is called capacitor volume. Discharging: positive and negative charges at both ends of capacitors are neutralized through conductors. During discharge, there is a transient current on the wire. Capacitor charge  - The capacitive reactance of capacitors is inversely proportional to frequency and capacity. When analyzing the capacitance, the frequency and capacity of the contacting signal must be analyzed. Formula of parallel plate capacitor The dielectric constant of vacuum εr=1, k is a constant of hydrostatic power, s is the positive area of two plates, and d is the distance between two plates. Explanation: the electric field in the parallel plate capacitor is uniform electric field. II. Functions of capacitor in electrical circuits In DC circuits, the effect of a capacitor is equivalent to a open circuit. Capacitors are one of the most commonly used electronic components to store charge. Capacitors are used in electronic circuits as low-pass, high-pass and band filters. A filter is a circuit that allows current and voltage of a specified frequency and waveform to pass through. A capacitor's reactance is inversely proportional to frequency. By controlling or changing the reactance, you can control the frequency allowed through the circuit. Capacitors also play a significant role in high-speed switching logic circuits. Such circuits' voltage level, which should be steady, can change with current fluctuation, thereby introducing noise or error signals. Decoupling capacitors are built into circuits to stabilize the current, minimizing noise signals. The effect of capacitor links with the structure of itself. The simplest capacitors are made up of polar plates at both ends and insulating dielectric (including air) at the middle. After electrification, the plate is charged, forming a voltage (potential difference), but the entire capacitor is non-conductive because of the intermediate insulation. However, the condition is that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulated, and when the voltage at both ends of the material increases to a certain extent, the material can conduct electricity. We call this voltage a breakdown voltage. When the capacitor is broken down, it is not an insulator. However, in AC circuits, the direction of the current changes with time, that is, this change has functional relation. The charging and discharging process of capacitors is time-dependent, and at this time, a varying electric field is formed between the plates, and this electric field is a function of the change with time. In fact, the current passes between capacitors in the form of an electric field. III. How to use capacitors? As a relatively common electronic component, capacitors have a wide range of uses. The following content gives you a brief introduction to the 9 most common scenarios where capacitors are used: Stopping DC, bypass (decoupling), coupling, filtering, temperature compensation, timing, tuning, rectifier, and energy storage. 1.Stopping DC: the function is to prevent the passage of DC and allow the AC to pass through. DC blocking capacitor 2. Bypass (decoupling): it provides a low impedance path for some parallel components in AC circuits.       Signal input and output   3. Coupling: as a connection between two circuits, AC signals are allowed to pass and transmitted to the next stage of the circuit. Coupling capacitor circuit model Capacitor as coupling component The purpose of using capacitor as coupling part is to transmit the front stage signal to the next stage, and to separate the influence of the DC of the former stage on the latter stage, so that the circuit is simple to debug and its performance is stable. The amplification of AC signal without capacitor will not changed, but the work points at all levels need to be redesigned. Because of the influence of the front and back stages, to debug at working points is very difficult and can hardly be realized at multistage. 4. Filtering: this is very important for the circuit, the capacitor behind the CPU is having this function basically. Impedance formula(filtering circuit) That is, the larger the frequency f, the smaller the impedance Z of the capacitance. At low frequency, the capacitance C can pass smoothly because of the large impedance Z, and at high frequency, the capacitance C is very small because of the impedance Z, which is equivalent to shorting the high frequency noise to the GND. 5. Temperature compensation: it improves the stability of the circuit by compensating for the influence of other components on the temperature adaptability.   Temperature compensation Analysis: because the capacity of the timing capacitor determines the oscillation frequency of the horizontal oscillator, the capacity of the timing capacitor must very stable and does not change with the humidity in the environment. Therefore, the capacitors with positive and negative temperature coefficients are used for temperature complementation. When the operating temperature increases, the capacity of Cl is increasing, while the capacity of C2 is decreasing, and the total capacity of two capacitors is the sum of the two capacitors after parallel connection. Because one capacity is increasing and the other is decreasing, the total capacity is basically stable. Similarly, when the temperature decreases, the capacity of one capacitor decreases while the other increases, and the total capacity is basically unchanged, which stabilizes the oscillation frequency and realizes the purpose of temperature compensation. 6. Timing: the use of capacitors in conjunction with resistors to determine the time constant of the circuit. Capacitor and resistor(timing) Inputting signal from low to high, after buffer 1 then input RC circuit. The characteristics of capacitor charging make the B point signal not change immediately with the input signal, but there is a gradual process of increasing. When it becomes larger to a certain extent, the buffer 2 flips over, resulting in a delay jump from low to high at the output end. 7. Tuning: having systematic tuning to circuits which related to frequency, such as cell phones, radios, and televisions. System tune Because the resonant frequency of the oscillation circuit is a functional relation of lc. It is fond that the ratio of maximum to minimum resonant frequency varies with the square root of capacitance ratio. Here the capacitance ratio refers to the ratio of the capacitance at the minimum reverse bias voltage to the capacitance at the maximum reverse bias voltage. Therefore, the tuning characteristic curve (bias voltage and resonant frequency) is basically a parabola. 8. Rectifier: switch on or off a semi-closed conductor component at a predetermined time. Rectification Filtering wave form 9. Energy storage: storage of electrical energy for release when necessary. For example, camera flashlights, heating devices, etc. (some capacitors now store energy at levels close to lithium batteries; a capacitor can store electricity as one-day power for a mobile phone.   IV. Capacitor types According to the analysis and statistics, capacitors are divided into the following 10 categories: 1. According to the structure: solid capacitor, variable capacitor and fine-tuned capacitor. 2. Classified by electrolytes: organic dielectric capacitor, inorganic dielectric capacitor, electrolytic capacitor, electrothermal capacitor and air-spaced capacitor. 3.According to the usage: high-frequency bypass  capacitor, low-frequency bypass  capacitor, filtering capacitor, tuning capacitor, high-frequency coupling capacitor, low-frequency coupling capacitor, small capacitor. 4. According to the different materials: ceramic capacitor, polyester capacitor, electrolytic capacitor, tantalum capacitor, advanced polypropylene capacitor etc. 5. High frequency bypass: ceramic capacitor, mica capacitor, glass film capacitor, polyester capacitor, glass-glazed capacitor. 6. Low frequency bypass: paper capacitor, ceramic capacitor, aluminum electrolytic capacitor, polyester capacitor. 7. Filter: aluminum electrolytic capacitor, paper capacitor, composite paper capacitor, liquid tantalum capacitor. 8. Tuning: ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors. 9. Low coupling: paper capacitor, ceramic capacitor, aluminum electrolytic capacitor, polyester capacitor, solid tantalum capacitor. 10. Small capacitors: metallized paper capacitor, ceramic capacitor, aluminum electrolytic capacitor, polystyrene capacitor, solid tantalum capacitor, glass-glazed capacitor, metallized polyester capacitor, polypropylene capacitor, mica capacitor. V. Capacitor volume Since capacitors are a container for storing charges, there is a problem of capacity. In order to measure the capacity of capacitors to store charges, the capacity is determined. A capacitor must store a charge under the action of an applied voltage. The amount of charge stored in different capacitors under voltage may also different. According to the international standard, when the capacitor is subjected to a 1V DC voltage, the value is the charge that can store in the the capacitor (that is, the electric quantity per unit voltage), which is expressed by the letter C. The basic unit of capacitance is the Farah (F). At 1V DC voltage, if the capacitor stores the charge is 1 Coulomb, the capacitance is set at 1 farah, and Farah is represented by the symbol F, 1 F=1 Q/ V. In practical application, the capacitance of capacitors is often much smaller than that of 1F, and is often used in smaller units, such as mF, μF, nF, pF, etc. The relationship between them is as follows:   1F=1000mF1mF=1000μF1μF=1000nF1nF=1000pF1F=1000000μF1μF=1000000pF VI. Charge and discharge of a capacitor When the capacitor is connected to the power supply, under the action of the electric field force, the free electron connected with the positive electrode of the capacitor moves through the power supply to the plate connected to the negative electrode of the power supply. The positive electrode is positively charged because of the loss of the negative charge; the negative electrode is negatively charged because of gaining negative charge. The positive and negative plates have the same charge size and the opposite sign, so the charge moves in a fixed direction to form a current. Due to the repulsive effect of the same charge, the initial current is maximum, and then decreases gradually. During the process of charge movement, the charge stored on the electrode plate of the capacitor increases continuously. When the voltage Uc between two poles of capacitor is equal to the power-supply voltage U, the charge stop moving. The current I=0, switch closed, through the wire connection, the capacitor plate charge neutralized. When K is closed, on the one hand, the positive charge of the capacitor C can be neutralized on the negative electrode; on the other hand, the negative charge of the negative electrode can also be moved to the positive electrode. The charge gradually decreases, the apparent current decreases and the voltage decreases to zero. VII. Matters needing attention when using capacitors Because the two poles of the capacitor have the residual charge, it is necessary to release the charge at first, otherwise the electric shock will occur easily. When dealing with the faulty capacitor, the circuit breaker and the upper and lower disconnector of the capacitor set should be opened first, and if the fuse protection is adopted, the fuse tube should be removed first. At this time, although the capacitor set has discharged  itself, there will still be part of the residual charge, therefore, it is necessary to carry out manual discharge. When discharging, the grounding end of the ground wire and the grounding grid should be fixed first, then the capacitor should be discharged with the grounding rod several times until there is no spark and discharge sound, and finally the ground wire is fixed again. Meanwhile, it should also be noted that if the capacitor has internal breakage, fuse failure or poor lead contact, there may be residual charges between the two poles, which will not be released during automatic discharge or manual discharge. Therefore, the operation or maintenance personnel should wear insulating gloves before contacting the faulty capacitor, and use a short line to connect the two poles of the fault capacitor to make it discharge. In addition, the capacitor with series connection should be discharged separately. VIII. Common fault of capacitor and treatment method (1) When the capacitor explodes, the power should cut off immediately and extinguish the fire with sand and dry-firefighter. (2) When the capacitor fuses, it shall report to the dispatch and open the circuit breaker of the capacitor after obtaining the consent. When the power supply is cut off to discharge it, external checks are carried out, such as whether there are flashover marks on the outside of the casing, whether the casing is deformed, the oil leakage and the short circuit of the earthing device, etc., and the insulation resistance between the poles and the ground is measured. Check whether the capacitor set connection is complete, firm, lacking of phase phenomenon. If not found fault phenomenon, it can be replaced after the investment. If the insurance still melts after power transmission, the faulty capacitor should be withdrawn and the rest should be power on. If the circuit breaker tripped at the same time as the fuse, at this time, don’t connect power supply. After the above inspection has been completed, the insurance must be replaced. (3) The circuit breaker of the capacitor tripped and the shunt safety was not broken, the capacitor should be discharged for three minutes before checking the power cable of the circuit breaker current inductor and the outside of the capacitor. If no anomaly is found, it may be due to external fault bus voltage fluctuations. After inspection, it may be put on trial; if not, a comprehensive test of the protection should be carried out. Through the above inspection, the test, if still can not find the reason, it is necessary to act according to the system, the capacitor is gradually tested. No trial test shall be made until the cause has been found.   FAQ   1. What is a capacitor used for? A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator).   2. What is capacitor and how it works? In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. ... Inside the capacitor, the terminals connect to two metal plates separated by a non-conducting substance, or dielectric.   3. When should you use a capacitor? Power Supply Smoothing. This is the easiest and very widely used application of a capacitor. ... Timing. If you supply power to a capacitor through a resistor, it will take time to charge. ... Filtering. If you pass DC through a capacitor, it will charge and then block any further current from flowing.   4. What is capacitor and its types? The most common kinds of capacitors are: Ceramic capacitors have a ceramic dielectric. Film and paper capacitors are named for their dielectrics. Aluminum, tantalum and niobium electrolytic capacitors are named after the material used as the anode and the construction of the cathode (electrolyte).   5. Are capacitors AC or DC? When we connect a charged capacitor across a small load, it starts to supply the voltage (Stored energy) to that load until the capacitor fully discharges. Capacitor comes in different shapes and their value is measured in farad (F). Capacitors are used in both AC and DC systems (We will discuss it below).   6. What is the principle of capacitor? A capacitor is a device that is used to store charges in an electrical circuit. A capacitor works on the principle that the capacitance of a conductor increases appreciably when an earthed conductor is brought near it. Hence, a capacitor has two plates separated by a distance having equal and opposite charges.   7. Are capacitors dangerous? Capacitors may store hazardous energy even after the equipment has been de-energized, and may build up a dangerous residual charge without an external source. "Grounding" capacitors in series, for example, may transfer (rather than discharge) the stored energy.   8. What type of capacitor should I use? The general rule is always use a capacitor with a higher working voltage than the circuit it is used in. This is of particular importance in power supply circuits with high value electrolytic capacitors. The working voltage should always exceed the peak working voltage of the circuit by a minimum of 20%.   9. What is capacitor and its applications? Capacitor is a basic storage device to store electrical charges and release it as it is required by the circuit. Capacitors are widely used in electronic circuits to perform variety of tasks, such as smoothing, filtering, bypassing etc…. One type of capacitor may not be suitable for all applications.   10. Do capacitors change AC to DC? No, capacitor cannot convert AC to DC. Capacitor can add DC to AC so that zero reference of AC signal can be changed, in other words capacitor works as level shifter.   11. Can Capacitors store AC? Capacitors do not store AC voltage - it stores voltage. It's rated to handle 450 VAC; that means it can withstand an AC voltage being applied to it. In other words, the capacitor is non-polar (it has no positive or negative lead). Polar (or polarized) capacitors are best known as "Electrolytic" capacitors.   12. What is the difference between a capacitor and a battery? A battery is an electronic device that converts chemical energy into electrical energy to provide a static electrical charge for power. Whereas a capacitor is an electronic component that stores electrostatic energy in an electric field.   13. How much current can a capacitor handle? A 3.5V charger will charge the capacitor up to 3.5V only. You need a higher voltage DC source to charge the capacitor to higher potential. Remember, in your case, 100V is the maximum which capacitor can handle.   14. What happens when a capacitor fails? During a failure, half of the capacitor could fail open, which would result in overall capacitance being lost. Or half of the capacitor could fail short, which would result in the overall capacitance being halved.   15. Does type of capacitor matter? Yes, the type of capacitor can matter. Different types of capacitor have different properties. Some of the properties that vary between capacitor types: a. Polarised vs unpolarised b. Max voltage c. Equivalent Series Resistance (ESR) d. Lifetime (electrolytics are particularly bad in this case) e. Physical size (e.g. a 100,000 uF ceramic capacitor would be HUGE!) f. Tolerance of capacitance (again, electrolytics are bad here, often being +/- 20%

The solid-state capacitor is called a solid-state aluminum electrolytic capacitor. The biggest difference between it and ordinary capacitors (i.e. liquid aluminum electrolytic capacitors) lies in the use of different dielectric materials. The dielectric materials of liquid aluminum capacitors are electrolyte, while the dielectric materials of solid capacitors are electroconductive polymer materials.   Electronic Basics #14: Capacitors Catalog I. Solid State Capacitor Introduction II. Solid State Capacitor Advantages III. Solid State Capacitor Types IV. Advantages and Disadvantages of Solid Capacitors FAQ   I. Solid State Capacitor Introduction   In view of the many problems of liquid electrolytic capacitance, the solid aluminum electrolytic capacitor has emerged as the times require. Since the 1990s, solid conducting polymer material has been used as cathode instead of electrolyte for aluminum electrolytic capacitor, which has achieved great development. The conductivity of conductive polymer materials is usually 2 ~ 3 orders of magnitude higher than that of electrolytes.    The application of aluminum electrolytic capacitors can greatly reduce the ESR and improve the features of temperature frequency, what’s more, because of the good processability of polymer materials, it is easy to be packaged. All greatly promote the development of aluminum electrolytic capacitance.   On the market, there are two types of aluminum electrolytic capacitors: organic semiconductor aluminum electrolytic capacitors (OS-CON) and polymer conductor aluminum electrolytic capacitors (PC-AC) (PC-CON).    The structure of an organic semiconductor aluminum electrolytic capacitor is similar to that of a liquid aluminum electrolytic capacitor; both are packaged in straight-pin and vertical configurations.   The difference is the cathode material of solid aluminum polymer electrolytic capacitor using the organic semiconductor extract, which can effectively solve the tough problems of electrolyte evaporation, leakage, flammability, and so on. Also, a solid aluminum polymer patch capacitor is a unique structure formed by combining the characteristics of aluminum electrolytic capacitance and tantalum capacitance.   Like liquid aluminum electrolytic capacitors, solid aluminum polymers are mostly in the form of patches. The film of polymer electrode with high conductivity is deposited on alumina as cathode, carbon, and silver as an extraction electrode, which is similar to the structure of solid tantalum electrolytic capacitance.     II. Solid State Capacitor Advantages   （1）With high stability, the solid aluminum electrolytic capacitor can work stably in a high-temperature environment, and improve the performance of the motherboard directly. At the same time, it is suitable for power filters because of its stable impedance in a wide temperature range, provides a stable and abundant power supply effectively, especially in overclocking.    Solid-state capacitors can work at high temperatures and maintain various electrical properties. The capacitance changes less than 15% in the whole temperature range, which is obviously superior to the liquid electrolytic capacitance. Meanwhile, the capacitance of solid-state electrolytic capacitor is independent of its working voltage, so it can work stably in the environment of voltage fluctuation.   （2）The solid-state aluminum electrolytic capacitor has an extremely long service life (over 50 years). It longer than the liquid aluminum electrolytic capacitance. And it will not be broken down, nor need to worry about liquid electrolyte drying and leakage affecting the stability of the motherboard. Solid-state electrolytes do not expand or even burn as liquid electrolytes do at high temperatures. Even if the temperature of the capacitor exceeds its limit, it just melts, which does not cause the capacitor metal shell to burst, so it is very safe.    The working temperature has a direct effect on the life of electrolytic capacitance. Advantages of its electrolyte make a longer service life than liquid electrolytic capacitor under different temperature conditions.   （3）Low ESR(Equivalent Series Resistance) and high mA rms are important indexes of capacitance. The lower the ESR, the faster the charge and discharge speed of capacitance. It directly affects the decoupling performance of the microprocessor power supply circuit, which is more obvious in high-frequency circuits. Therefore, it can be viewed the biggest difference between solid-state electrolytic capacitance and liquid capacitance.   Solid aluminum electrolytic capacitance with the lower ESR and energy dissipation under high power operation conditions can fully absorb the high amplitude voltage between the power lines in the circuit and prevent its interference to the system. When the CPU changes from a low power state to a full load state, the transient (generally less than 5 milliseconds) power required for this CPU switch comes from the CPU power supply circuit, at this moment, the high peak current can be output instantly by the high-speed charge-discharge characteristic of the solid-state capacitor, which can guarantee sufficient power supply and ensure the CPU to work stably.     III. Solid State Capacitor Types     According to the medium, capacitors can be divided into inorganic dielectric capacitors, organic dielectric capacitors, and electrolytic capacitors three categories.   1. Inorganic dielectric capacitors: including familiar ceramic capacitors and mica capacitors, we will often see ceramic capacitors on the CPU. Ceramic capacitors have excellent comprehensive properties and can be used in GHz-class UHF devices, such as CPU/GPU, thus its price is also very expensive.   2.Organic dielectric capacitors: such as thin-film capacitors, which are often used in loudspeakers with their precision, high temperature, and high-pressure resistance.   3. Electrolytic capacitors: known as aluminum capacitors. The traditional method of classifying electrolytic capacitors is based on anode materials, such as aluminum, tantalum, or niobium. However, this method of judging capacitance performance based on the anode is out of date. At present, the key to determine the performance of electrolytic capacitance lies not in the anode, but in the electrolytic, cathode. According to the classification of cathode materials, electrolytic capacitors can be divided into electrolyte, manganese dioxide, TCNQ organic semiconductors, solid polymer conductors, and so on.      IV. Breif Analysis of Advantages and Disadvantages of Solid Capacitors   The dielectric of liquid electrolytic capacitors is liquid electrolyte: liquid particles are very active at high temperatures and have a low boiling point relative to the internal pressure of the capacitor, making it easily explosible. The solid-state capacitance is made of polymer dielectric: at high temperatures, the particle growth and behavior of solid particles are lower than that of liquid electrolytes, and its boiling point will reach 350 degrees Celsius, making it almost impossible to burst.    The ESR of solid-state capacitance in high-frequency operation is shown to be very weak, and the conductivity is very fine. It has the properties of lowering impedance and producing less heat, which is the most obvious between 100KHz and 10MHz.   Traditional electrolytic capacitance is easily influenced by the operating environment's temperature and humidity, and it is less stable at high and low temperatures. The ESR of the solid capacitance can be as low as 0.0040.005 ohms between minus 55 and 105 degrees Celsius, but the electrolytic capacitance varies with temperature.   In terms of capacitance values, liquid capacitance would be lower than the indicated capacitance value below 20 degrees Celsius, and the lower the temperature, the lower the capacitance value. At minus 20 degrees Celsius, capacitance decreases by around 13%, and at minus 55 degrees Celsius, capacitance decreases by 37%. Since solid capacitance decreases by less than 5% at minus 55 degrees, solid state capacitors are guaranteed not to be harmed by lower temperatures. The low-frequency response of solid-state capacitance is not as good as electrolytic capacitance.     In other words, a motherboard with all-solid-state capacitance is not the most reasonable. Whether solid or electrolytic capacitors, their main function is to filter clutter, so long as the capacity and quality of capacitance can reach certain requirements, it can also ensure a stable operation. Solid-state capacitors at 105C have the same lifetime as electrolytic capacitors for 2000 hours.    When the temperature drops, their lives increase, but the solid-state capacitors increase even more. In general, the operational temperature of the capacitor is 70 degrees or less. In addition, the service life of solid-state capacitance can last 23 years, almost six times than the electrolytic capacitance. Compared with electrolytic capacitors, the capacity of electrolytic capacitors is much larger than that of solid capacitors at the same volume and voltage.     At present, solid capacitors are mostly used in the CPU power supply of computer motherboard, but the capacity redundancy is very little, it is necessary to improve the switching frequency of the part of the CPU power supply. Both solid and electrolytic capacitors will have the problem of capacity attenuation in the process of use. However, although the capacity of the circuit board with solid-state capacitance fluctuates slightly, the power supply will appear ripples, which will cause the CPU to work improperly.     Therefore, the lifetime of the solid-state capacitor is very high theoretically, but not in practice. Maintenance when using solid-state capacitor computer board: the power supply part of the CPU is often connected with multiple capacitors, so the solid-state capacitance will not have deformation, explosive slurry, leakage, etc. There is no way to determine which one is out of order basically. Therefore, in maintenance, one of them is often removed (no matter good or bad), and a large-capacity capacitor can be replaced (often with electrolytic capacitance). This method can usually solve the problem quickly.      In theory, the lifetime of the solid-state capacitor is very long, but there will still be a lot of faults in the process of practical use. At present, it seems that most motherboards with overclocking as the selling point put forward by many manufacturers will use solid-state capacitors. But it is not the capacitance that determines the performance of the CPU. The design of the circuit, the development of BIOS, the quality of the CPU itself, and the heat dissipation measures may determine the success or failure of the CPU.   FAQ   1. What is a solid state capacitor? The full name of a solid capacitor is a conductive polymer aluminum electrolytic capacitor, also called a polymer aluminum capacitor. It is currently the highest level of capacitor products. The dielectric material of the solid capacitor is a functional conductive polymer, which can greatly improve the product.   2. Are Solid Capacitors better? Solid capacitors have a higher tolerance not only for higher temperatures, but they also perform better with higher frequencies and higher current than electrolytic capacitors. ... Because there is less impedance at higher frequencies, solid capacitors are more stable and generate less heat than electrolytic capacitors.   3. How do you read a solid state capacitor? If you have a capacitor that has nothing other than a three-digit number printed on it, the third digit represents the number of zeros to add to the end of the first two digits. The resulting number is the capacitance in pF. For example, 101 represents 100 pF: the digits 10 followed by one additional zero.   4. What do you need to know about solid state capacitors? Solid-state capacitors have already gone down the altar. Many common electronic and digital products use these products in large quantities. The solid-state capacitors are similar to the common aluminum electrolytic capacitors, some are replaceable, and there is a solid capacitor, sheet, for Replace the common tantalum capacitor.   5. Which is the best electrolytic capacitor for motherboard? Solid aluminum electrolytic capacitors can directly improve the performance of the motherboard. At the same time, it is suitable for power supply filtering due to its stable impedance over a wide temperature range. It can effectively provide a stable and abundant power supply, which is especially important in overclocking.   6. How do you read a solid state capacitor? If you have a capacitor that has nothing other than a three-digit number printed on it, the third digit represents the number of zeros to add to the end of the first two digits. The resulting number is the capacitance in pF. For example, 101 represents 100 pF: the digits 10 followed by one additional zero.   7. What is the average lifespan of a capacitor? Design lifetime at rated temperature. Manufacturers of electrolytic capacitors specify the design lifetime at the maximum rated ambient temperature, usually 105°C. This design lifetime can vary from as little as 1,000 hours to 10,000 hours or more.   8. What metals are capacitors made of? There are three different anode metals in use for electrolytic capacitors: Aluminum electrolytic capacitors use a high-purity etched aluminium foil with aluminium oxide as dielectric. Tantalum electrolytic capacitors use a sintered pellet (“slug”) of high-purity tantalum powder with tantalum pentoxide as dielectric.   9. When should you use a capacitor? Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies.   10. How do I choose the right size capacitor? You mainly need to look at 2 values: the voltage and the capacity -both are written on most capacitors-. For example, if you are going to charge a capacitor with 24V, you need to make sure your capacitor will support that voltage; so you'll need a capacitor for at least 25V (plus error margin).       You May Also Like Operational Amplifier(OP Amp) Tutorial Instructions of Common problems in the Application of Inverter About Operational Amplifier LM358: 24 Classical Circuits DIY Community:  DIY Capacitor Flux Capacitor - Back TO The Future