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Ⅰ Introduction   A capacitor is an electrical device that stores energy as an electric field. It consists of two metal plates separated by a dielectric or non-conducting material. Fixed capacitance and variable capacitance are the two broad categories of capacitors. The most common are fixed capacitance capacitors, but variable capacitance capacitors are also available. Rotary or trimmer capacitors are examples of these. Fixed capacitance capacitors are classified as film capacitors, ceramic capacitors, electrolytic capacitors, and superconductor capacitors. Follow the link to learn more about the various types of capacitors. This article goes into greater detail about the ceramic capacitor.     Images of  Capacitors     Catalog Ⅰ Introduction Ⅱ Ceramic Capacitor Basics 2.1 What is a Ceramic Capacitor? 2.2 Ceramic Capacitor Polarity and Symbol 2.3 Types and Properties of Ceramic Capacitors 2.4 Ceramic Capacitor  Classes Ⅲ Why Ceramic Capacitors Mostly Used in Electronic Circuit than Others? 3.1 Applications and Uses of Ceramic Capacitor 3.2  Properties or Advantages of Ceramic Capacitors Ⅳ How to Read Ceramic Capacitor? 4.1 Where to Use a Ceramic Capacitor? 4.2 How We Read Ceramic Capacitor Value？ 4.3 Calculate Ceramic Capacitor Value 4.4 Some Examples Ⅴ FAQ     Ⅱ Ceramic Capacitor Basics   2.1 What is a Ceramic Capacitor?   The capacitor value is unchangeable.  The working ceramic material acts as the dielectric, and it is a ceramic capacitor constructed of two or more alternating layers of ceramic and it has a metal layer acting as the electrodes, and the composition of the ceramic material defines the electrical behavior and thus applications.   As per below video of ceramic capacitors:     What is CERAMIC Capacitor _ Uses _ complete information in English     2.2 Ceramic Capacitor Polarity and Symbol   Ceramic capacitors are the most common type of capacitor found in all electrical devices, and they use a ceramic material as the dielectric. Ceramic capacitors are non-polarity devices, which means they have no polarities. As a result, we can connect it to a circuit board in any direction.   As a result, they are far safer than electrolytic capacitors. The symbol for a non-polarised capacitor is shown below. Many capacitors, such as tantalum beads, do not have polarity.     Ceramic Capacitor Polarity and Symbol       2.3 Types and Properties of Ceramic Capacitors   Ceramic capacitors come in three varieties, though other styles are available:   Resin-coated leaded disc ceramic capacitors for through-hole mounting.Multi-Layer Ceramic Capacitors with Surface Mount (MLCC).Microwave bare lead-free disc ceramic capacitors that are designed to fit into a PCB slot.   different types of ceramic capacitors     Ceramic disc capacitors   Ceramic disc capacitors are made by coating a ceramic disc on both sides with silver contacts. These devices can be made from multiple layers to achieve higher capacitances. Ceramic disc capacitors are typically through-hole components that are dwindling in popularity due to their size. If capacitance values allow, MLCCs are used instead. Ceramic disc capacitors have capacitance values ranging from 10pF to 100F and voltage ratings ranging from 16 volts to 15 kV and higher.   Multi-layer ceramic capacitor (MLCC)   MLCCs are fabricated by precisely combining finely ground granules of paraelectric and ferroelectric materials and then layering the mixture with metal contacts. Following the completion of the layering, the device is heated to a high temperature and the mixture is sintered, resulting in a ceramic material with the desired properties. The resulting capacitor is essentially made up of many smaller capacitors connected in parallel to increase the capacitance. MLCCs have 500 layers or more, with a minimum layer thickness of about 0.5 microns. As technology advances, layer thickness decreases, and higher capacitances for the same volume are achieved.     2.4 Ceramic Capacitor  Classes   Different ceramic capacitor classes are defined based on the working temperature range, temperature drift, and tolerance:   Class 1 Ceramic Capacitors   These are the most temperature-stable capacitors. They have nearly linear properties.The most commonly used dielectric compounds are.Magnesium Titanate is used to achieve a positive temperature coefficient.Calcium Titanate is used in capacitors that have a negative temperature coefficient.   Class 2 Ceramic Capacitors   Class 2 capacitors perform better at the price of volumetric efficiency, but at the expense of lower accuracy and stability. As a result, they are typically used for decoupling, coupling, and bypass applications where precision is not critical.Temperature range: -50 to +85 degrees CelsiusThe dissipation factor is 2.5 percent.Accuracy ranges from average to poor.   Class 3 Ceramic Capacitors   Class 3 ceramic capacitors have a high volumetric efficiency but a low dissipation factor. It is unable to withstand high voltages. Barium Titanate is a common dielectric.Temperature range of +10C to +55C will cause a -22% to +50% change in capacitance for a Class 3 capacitor.Dissipation factor: 3 to 5%.It will have a low level of accuracy (typically 20% or -20/+80%).   Class 3 is typically used for decoupling or in other power supply applications where accuracy is not critical.     Ⅲ Why Ceramic Capacitors Mostly Used in Electronic Circuit than Others?   Many circuits, particularly electronic circuits, use ceramic capacitors, as you may have noticed. Ceramic capacitors are largely used over electrolytic or other capacitors.   Ceramic capacitors     3.1 Applications and Uses of Ceramic Capacitor   In electronic sensor circuits, ceramic capacitors are used.Ceramic capacitors are used in the transmission and reception of electronic signals.Ceramic capacitors are applied in circuits such as audio mixers, controllers, and equalizers.Ceramic capacitors are suitable for frequency-dependent circuits, such as electronic filter circuits, audio circuits, radio signal transmitters, and receiver circuits. Resonant circuits, like radio frequency communication system, needs ceramic capacitors, too.Ceramic capacitors are used in alternating current circuits for no polarity such as high voltage protection circuits, power circuit breakers, and so on.Ceramic capacitors are used in direct current motors to reduce radio frequency noise.Ceramic capacitors can also be used as Bypass Capacitors.Why Ceramic Capacitors mostly used in Electronic Circuit?     3.2  Properties or Advantages of Ceramic Capacitors   Ceramic capacitors are available in extremely small sizes, which is a significant benefit. Because of the numerous electronic circuits, in fact, most modern electronic circuits necessitate the use of small size capacitors.   Many critical electronic circuits necessitate the use of very small capacitors. Ceramic capacitors are available in a wide range of sizes.   Ceramic capacitors can provide very high stability; in fact, they offer a wide range of stability.   Ceramic capacitors have a low temperature coefficient and a higher voltage breakdown characteristic.        5. Ceramic capacitors are the best choice for high-frequency applications.     Ⅳ How to Read Ceramic Capacitor?   Two reference tables   MarkingCapacitance (pF)Capacitance (ìF)101100 pF0.0001 ìF221220 pF0.00022 ìF471470 pF0.00047 ìF1021,000 pF0.001 ìF2222,200 pF0.0022 ìF4724,700 pF0.0047 ìF10310,000 pF0.01 ìF22322,000 pF0.022 ìF47347,000 pF0.047 ìF104100,000 pF0.1 ìF224220,000 pF0.22 ìF474470,000 pF0.47 ìF1051,000,000 pF1 ìF2252,200,000 pF2.2 ìF4754,700,000 pF4.7 ìF     Letter printed capacitor indicate tolerance LetterToleranceA±0.05 pFB±0.1 pFC±0.25 pFD±0.5 pFE±0.5%F±1%G±2%H±3%J±5 %K±10%L±15%M±20%N±30%P–0%, + 100%S–20%, + 50%W–0%, + 200%X–20%, + 40%Z–20%, + 80%     4.1 Where to Use a Ceramic Capacitor?   Ceramic capacitors are applied in a variety of applications. It is primarily used for filtration. It is used in a signal or frequency circuit to filter and purify the signal. It can convert a direct current to a direct current. The ceramic capacitor is a genre of energy storage device. It stores the DC while passing the AC. This is what the ceramic capacitor looks like.     4.2 How We Read Ceramic Capacitor Value？     alphabetic code     The first is an alphabetic code that indicates the component's tolerance. The second is a numeric code that tells us the actual capacitance of the capacitor.   So let's take a look at our example right now. In our example, the value is 102 k. The first significant digit in the code is one, and the second significant digit is zero. As a result, these are the numbers in front of our multiplier.         How to read the values of Ceramic Capacitors?   4.3 Calculate Ceramic Capacitor Value   So, if we take your multiplier, which is two, and looks at the chart, that equals two zeros. As a result, we append two zeros to the end of the number. So, picofarad, it's 1000. Now, K represents our component tolerance, which in this case is plus or minus 10%. So that's how we figure out the capacitor's size and rating.   Now I'm going to show you how to use a multimeter to measure the capacitance of a capacitor. In this example, I'm using a capacitor with the numerical value 103 written on it, which equals 10-nanofarads.       nine ferrites   When you look at the display of what is rated, you'll notice that its practical rating is it works, and it has nine ferrites. So tolerances are around 10%. When you connect it to your actual multimeter, In this one, make sure you have an appropriate terminal. As you can see, I have the capacitance symbol in the bottom right-hand corner. Then, make sure your multimeter is set to the appropriate range. Then double-check that you've selected the correct option.   Ceramic disk capacitor codes table   Picofarad pFNanofarad nFMicrofarad FCode100.010.00001100150.0150.000015150220.0220.000022220330.0330.000033330470.0470.0000474701000.10.00011011200.120.000121211300.130.000131311500.150.000151511800.180.000181812200.220.000222213300.330.000333314700.470.000474715600.560.000565616800.680.000686817500.750.000757518200.820.00082821100010.00110215001.50.0015152200020.00220222002.20.002222233003.30.003333247004.70.0047472500050.00550256005.60.005656210000100.110215000150.01515222000220.02222333000330.03333347000470.04747368000680.0686831000001000.11041500001500.151542000002000.22542200002200.222243300003300.333344700004700.474746800006800.68684100000010001105150000015001.5154200000020002205220000022002.2225330000033003.3335470000047004.7475   The final number written on a ceramic capacitor is the power of ten multiplied by the first two numbers. If a ceramic capacitor has the code 682, First, look at the last number. So, as we can see, the final number is 2. The multiplier is now 102.   4.4 Some Examples   204 = 20×104 = 200000 PF 472 = 47×102 = 4700 PF 502 = 50×102 = 5000 PF 330 = 33×100 = 33 PF   [100 = 1] UNITS   1000 nanofarad(nF) = 1 microfarad(µF) 1 picofarad = 10-12farads. Nano= 10-9 Micro= 10-6 1 Nano Farad= 10-9 Farad 1 Microfarad (µF)= 10-6 Farad 1 nF = 1000 pF 1 pF = 0.001 nF   Example:   convert 15 nF to pF: 15 nF = 15 × 1000 pF = 15000 pF   Capacitor voltage code   0G4VDC0L5.5VDC0J6.3VDC1A10VDC1C16VDC1E25VDC1H50VDC1J63VDC1K80VDC2A100VDC2Q110VDC2B125VDC2C160VDC2Z180VDC2D200VDC2P220VDC2E250VDC2F315VDC2V350VDC2G400VDC2W450VDC2H500VDC2J630VDC3A1000VDC   Ⅴ FAQ   1. What is ceramic capacitor used for? Ceramic capacitors are used for all types of circuits in a number of applications. There are four main capacitor applications that are described in detail below: coupling, decoupling, smoothing, and filtering.   2. Do ceramic capacitors go bad? Like mica capacitors, ceramic capacitors also very rarely go bad. Do not replace ceramic disc capacitors unless you are sure one has gone bad. ... While replacing the capacitors, check the radio's resistors. Since you will be replacing the capacitors, you should snip one lead of each paper and electrolytic capacitor.   3. Why do ceramic capacitors fail? Ceramic capacitors can fail in a couple of ways. They can be mechanically damaged - too much physical stress (pressure on the part or the board is bent a little too much) can cause a crack. The capacitor will then develop short circuits between layers. It acts more like a resistor in that case.  4. 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. 5. What is the practical use of capacitor? The most common use for capacitors is energy storage. Additional uses include power conditioning, signal coupling or decoupling, electronic noise filtering, and remote sensing. Because of its varied applications, capacitors are used in a wide range of industries and have become a vital part of everyday life.  6. Why capacitor is not used as battery? 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. 

Introduction The rectifier diode is a semiconductor device that converts AC into DC. Usually it contains a PN junction with two terminals, a positive electrode and a negative electrode. The most important characteristic is unidirectional conductivity. In electronic circuits, its breakdown voltage is high, the reverse leakage current is small, and the high temperature performance is good. Generally, it can be made of materials such as semiconductor germanium or silicon. In addition, high-voltage and high-power rectifier diodes are made of high-purity single crystal silicon (it is easy to reverse breakdown when there is more doping). This kind of device has a large junction area and can pass a large current (up to thousands of amperes), but the operating frequency is not high, generally below tens of KHz. Rectifier diodes are mainly used in various low-frequency half-wave rectifier circuits. If require full-wave rectification, several diodes need to be connected to form a rectifier bridge. What is a Rectifier? (AC to DC) Catalog Introduction Ⅰ Common Parameters Ⅱ Rectifier Diodes Selection Ⅲ Rectifier Common Failures Ⅳ Rectifier Diodes Detection Ⅴ Rectifier Diode Replacement 5.1 Replacing Rules 5.2 Commonly Used Rectifier Models List Ⅵ Rectifier Diode Circuit Types 6.1 Half-Wave Rectifier Circuit 6.2 Full-Wave Rectifier Circuit 6.3 Bridge Rectifier Circuit Ⅶ High-frequency Rectifier Diodes Ⅷ FAQ Ⅰ Common Parameters The rectifier diode uses the unidirectional conductivity of the PN junction to convert alternating current into pulsating direct current. Rectifier diodes have a large leakage current, and most of them are diodes packaged with surface mount materials. The parameters of the rectifier diode include the maximum rectifier current, which refers to the maximum current value allowed by the rectifier diode for long-term operation. It is the main parameter of the rectifier diode and the main basis for the option of the rectifier diode. Except it, other important parameters are introduced here.(1) Maximum average rectified current IF: It refers to the maximum forward average current allowed to pass through the diode during long-term operation. The current is determined by the PN junction area and the heat dissipation conditions. It should be noted that the average current passing through the diode cannot be greater than this value, and has heat dissipation.(2) Maximum reverse working voltage VR: It refers to the maximum reverse voltage allowed to be applied across the diode. If it is greater than this value, the reverse current (IR) will increase sharply, and the unidirectional conductivity of the diode will be destroyed, causing reverse breakdown. Usually take half of the reverse breakdown voltage VB as VR.(3) Maximum reverse current IR: It is the reverse current allowed to flow through the diode under the highest reverse working voltage. This parameter reflects the quality of the unidirectional conductivity of the diode. Therefore, the smaller the current value, the better the diode quality.(4) Breakdown voltage VB: It refers to the voltage value at the sharp bend point of the reverse volt-ampere characteristic curve of the diode. When the reverse is a soft characteristic, it refers to the voltage value under a given reverse leakage current condition.(5) The highest operating frequency fm: It is the highest operating frequency of the diode under normal conditions. It is mainly determined by the junction capacitance and diffusion capacitance of the PN junction. If the operating frequency exceeds fm, the unidirectional conductivity of the diode will not be well reflected.(6) Reverse recovery time trr: It refers to the reverse recovery time under the specified load, forward current and maximum reverse transient voltage.(7) Zero-bias capacitor CO: It refers to the sum of the capacitance of the diffusion capacitance and the junction capacitance when the voltage across the diode is zero. It is worth noting that, due to the limitation of the manufacturing process, even the same type of diode has a large dispersion of its parameters. The parameters given in the manual are often within a range. If the test conditions change, the corresponding parameters will also change. For example, the IR of the 1N5200 series silicon plastic rectifier diode measured at 25°C is less than 10uA, and at 100°C IR becomes less than 500uA.     Ⅱ Rectifier Diodes Selection Rectifier diodes are generally planar silicon diodes, which are used in various power rectifier circuits. When selecting a rectifier diode, the parameters such as its maximum rectifier current, maximum reverse working current, cut-off frequency and reverse recovery time should be mainly considered.The rectifier diode used in the ordinary series stabilized power supply circuit does not require high reverse recovery time of the cut-off frequency. The rectifier diode with the maximum rectified current and maximum reverse working current should meet the requirements of the circuit.The rectifier diode used in the rectifier circuit of the switching regulated power supply and the pulse rectifier circuit should be a rectifier diode with a higher operating frequency and shorter reverse recovery time (such as RU series, EU series, V series, 1SR series, etc.) or select fast recovery diodes, or Schottky rectifier diode.     Ⅲ Rectifier Common Failures (1) Inadequate lightning protection and poor overvoltage protection. The rectifier device is not equipped with lightning protection and overvoltage protection devices. Or insufficient routine maintenance of the equipment.(2) Poor operating conditions. In the indirect drive generator set, because the calculation of the speed ratio is incorrect or the ratio of the diameters of the two belt pulleys does not meet the requirements of the speed ratio, the generator runs at a high speed for a long time, so the rectifier is at a higher voltage for a long time. It accelerates the rectifier aging, and was damaged by premature breakdown.(3) Poor operation management. The load failure or diode breakdown doesn’t fixed in time.(4) Poor equipment installation or manufacturing process. The generator set has been operating under large vibration for a long time, which affects the rectifier tube operation. At the same time, because the generator set speed is unstable, the working voltage of the rectifier tube also fluctuates, which greatly accelerate the aging and damage of the rectifier tube.(5) The specifications and models of the rectifier tube do not match. When replacing a new rectifier tube, wrongly replace the tube whose working parameters do not meet the requirements or the wiring is wrong, causing the rectifier tube to breakdown and damage.(6) The safety margin of the rectifier tube is too small. The overvoltage and overcurrent safety margin of the rectifier tube is too small, so that the rectifier tube cannot withstand the overvoltage or the peak value of the overcurrent transient process that occurs in the generator excitation circuit and is damaged. Figure 1. Diode as Rectifier Symbol     Ⅳ Rectifier Diodes Detection Here is a more general and simple method. Remove all the rectifier diodes in circuit, use the 100×R or 1000×R ohm range of a multimeter to measure the two lead wires of the rectifier diode (adjust and test twice). If the resistance values measured twice are very different, for example, the resistance value is as high as a few hundred kΩ to infinity, or the resistance value is only a few hundred Ω or less, indicating that the diode is good (except under special circumstances). If the resistance value measured twice is almost the same and the resistance value is very small, it means that the diode has been broken down and cannot be used. In addition, if the resistance values measured twice are both infinite, it means that the diode has been internally disconnected and cannot be used.     Ⅴ Rectifier Diode Replacement   5.1 Replacing Rules After the rectifier diode is damaged, you should replace with the same model or another model with the same parameters.Generally, rectifier diodes with high withstand voltage (reverse voltage) can be substituted for rectifier diodes with low withstand voltage, while rectifier diodes with low withstand voltage cannot be replaced with rectifier diodes with high withstand voltage. A diode with a high rectification current value can be substituted for a diode with a low rectification current value, while a diode with a low rectification current value cannot be substituted for a diode with a high rectification current value.   5.2 Commonly Used Rectifier Models List Material Model Reverse Voltage Operation (peak) Average Rectified Current   Silicon Rectifier Diode 1N4001 50V 1A (Ir=5uA,Vf=1V,Ifs=50A) 1N4002 100V 1A 1N4003 200V 1A 1N4004 400V 1A 1N4005 600V 1A 1N4006 800V 1A 1N4007 1000V 1A 1N4148 75V 4PF, Ir=25nA,Vf=1V 1N5391 50V 1.5A (Ir=10uA,Vf=1.4V,Ifs=50A) 1N5392 100V 1.5A 1N5393 200V 1.5A 1N5394 300V 1.5A 1N5395 400V 1.5A 1N5396 500V 1.5A 1N5397 600V 1.5A 1N5398 800V 1.5A 1N5399 1000V 1.5A 1N5400 50V 3A (Ir=5uA,Vf=1V,Ifs=150A) 1N5401 100V 3A 1N5402 200V 3A 1N5403 300V 3A 1N5404 400V 3A 1N5405 500V 3A 1N5406 600V 3A 1N5407 800V 1A (Ir=5uA,Vf=1V,Ifs=50A) 1N5408 1000V 1A   Ⅵ Rectifier Diode Circuit Types The power grid supplies users with alternating current, and various electrical devices require direct current. Rectification is the process of converting AC into DC. Utilizing the device with unidirectional conductivity, the current of alternating direction and magnitude can be converted into direct current. The following introduces three main rectifier circuits composed of crystal diodes.   6.1 Half-Wave Rectifier Circuit Figure 2. Half-Wave Rectifier Circuit The figure shows the simplest rectifier circuit. It is composed of power transformer B, rectifier diode D and load resistor Rfz. The transformer transforms the voltage into the required alternating voltage e2, and then D transforms the AC into pulsating DC.The transformer threshold voltage e2 is a sine wave voltage whose direction and magnitude change with time, and its waveform is shown in Figure (a). In the 0~K time, e2 is a positive half cycle, that is, the upper end of the transformer is positive and the lower end is negative. At this time, the diode is in forward conductive conduction, and e2 is added to the load resistor Rfz through it. Within π~2π, e2 is in negative half cycle, the lower end of the transformer secondary is positive, and the upper end is negative. At this time, D bears the reverse voltage and does not conduct, and there is no voltage on Rfz. In the time of π~2π, the process of 0~π time is repeated, and in the time of 3π~4π, the process of π~2π time... half-cycle through Rfz, a single right direction voltage is obtained on Rfz (up positive and lower negative), as shown in Figure (b), which achieves the purpose of rectification. But the load voltage Usc, and the load current also changes with time, so it is usually called pulsating DC. Figure 3. Half-Wave Rectifier Wave This rectification method of removing the first half week and leaving half a week is called half wave rectification. It is not difficult to note that the half-wave rectification is at the expense of consuming half of the AC in circuit, and the current utilization rate is very low. According to it, half-wave rectifier diode is commonly used in high voltage and small current occasions, and is rarely used in general radio devices.   6.2 Full-Wave Rectifier Circuit Figure 4. Full-Wave Rectifier Circuit If some adjustments are made to the structure of the rectifier circuit, a full-wave rectifier circuit that can be obtained. The figure above is the electrical schematic diagram of the full-wave rectifier circuit.The full-wave rectifier circuit can be regarded as a combination of two half-wave rectifier circuits. A tap needs to be drawn in the middle of the secondary coil of the transformer to divide the secondary coil into two symmetrical windings, so as to get two voltages e2a and e2b of equal size but opposite polarity to form two energized circuits.The working principle of the full-wave rectifier circuit can be illustrated by the waveform diagram. Between 0 and π, e2a is a positive voltage to Dl, D1 is turned on, and a up positive and down negative voltage is obtained on Rfz. e2b is a reverse voltage to D2, and D2 is not conductive (see Figure(b) ). In the time of π-2π, e2b is a positive voltage to D2, D2 is turned on, and the voltage obtained on Rfz is still up positive and down negative voltage, therefore e2a is a reverse voltage to D1, and D1 is not conductive (see figure (c). Figure 5. Full-Wave Rectifier Circuit Wave Repeated this way, because the two rectifier elements D1 and D2 conduct electricity in turn, the result is that the load resistor Rfz has the same direction of current at the positive and negative half cycles, as shown in Figure(b). This is full-wave rectification, which not only uses the positive half-cycle, but also cleverly uses the negative half-cycle. Full-wave rectifier greatly improves the rectification efficiency. Figure 6. Full-Wave Rectifier Circuits This circuit requires the transformer to have a secondary center tap that makes the two ends symmetrical, which brings a lot of trouble to the production. In addition, in this circuit, the maximum reverse voltage that each rectifier diode can withstand is twice the maximum value of the transformer secondary voltage, so diodes should withstand higher voltages.   6.3 Bridge Rectifier Circuit Figure 7. Bridge Rectifier Circuit The bridge rectifier circuit is the most used rectification circuit. It has the advantages of a full-wave rectifier circuit as long as two diode ports are connected to form a bridge structure, so its shortcomings are overcome to a certain extent.The bridge rectifier circuit is as follows: Figure 8. Bridge Rectifier Circuit (a) When e2 is a positive half cycle, D1, D3 and the direction voltage, D1, D3 are turned on; D2, D4 are applied with reverse voltage, they are turned off. E2, Dl, Rfz, and D3 are energized a loop in the circuit. On Rfz, a positive and negative half-wave washing voltage is formed. When e2 is a negative half cycle, a positive voltage is applied to D2 and D4, and they are turned on; Apply reverse voltage to D1 and D3, they are cut off. E2, D2Rfz, and D4 are energized a loop in the circuit, and the other half-wave rectified voltage is also formed on Rfz. Figure 9. Bridge Rectifier Circuit (b) If repeated, a full-wave rectified voltage at Rfz is made. The waveform diagram is the same as the full-wave rectifier. It is not difficult to see from the figure that the reverse voltage of each diode in the bridge circuit is equal to the maximum value of the secondary voltage of the transformer, which is half smaller than the full-wave cleaning circuit.     Ⅶ High-frequency Rectifier Diodes The rectifier diode in the switching power supply must have the characteristics of low forward voltage reduction and fast recovery, and should also have sufficient output power. The following three types of high-frequency diodes can be used: fast recovery rectifier, ultra-fast recovery rectifier, and Schottky diode rectifier.Fast recovery and ultra-fast recovery rectifier diodes have moderate and high forward voltage drop, and the range is from 0.8 to 1.2V. These two types of rectifier diodes also have higher cut-off voltage parameters. Therefore, they are particularly suitable for use in low-power auxiliary power circuits with output voltages around 12V.Compared with general rectifier diodes, the reverse recovery time difference between fast recovery rectifier diodes and ultra-fast recovery rectifier diodes is reduced to the nanosecond level, thus greatly improving the efficiency of the power supply. According to experience, when choosing a fast recovery rectifier diode, its reverse recovery time should be at least 1/3 of the rise time of the switching transistor. These two kinds of rectifier diodes also reduce the switching voltage spike, because it will affect the ripple of the output DC voltage.Whether fast recovery rectifier diodes and ultra-fast recovery rectifier diodes used in switching power supplies need a heat sink, which depends on the maximum power of the circuit. Under normal circumstances, the allowable junction temperature is 175°C during manufacture. The manufacturer has a technical parameters provided for the designer to calculate the maximum output operating current, voltage, and case temperature. Even under the action of a large forward current, the forward voltage drop of Schottky rectifier diodes is very low, only about 0.4V. Moreover, as the junction temperature increases, its forward voltage drop decreases. Therefore, Schottky rectifier diodes are particularly suitable for low-voltage output circuits around 5V. Its reverse recovery time is negligible, because this device is a semiconductor device with majority carrier. During the switching process of the device, there is no need to remove the stored charge of the minority carrier.Schottky rectifier diodes have two major shortcomings: First, the reverse cut-off voltage tolerance is low, about 100V; second, the reverse leakage current is large, making the device more susceptible to have heat breakdown than other types of rectifier devices. Of course, these shortcomings can also be overcome by adding a transient overvoltage protection circuit and appropriately controlling the junction temperature.     Ⅷ FAQ 1. How does a rectifier diode work?A rectifier is a device that converts an Alternating Current (AC) into a Direct Current (DC) by using one or more contact diodes. ... In simple words, a diode allows current in just one direction. This unique property of the diode allows it to act sort of a rectifier by converting an alternating current to a DC source.   2. What is a function of rectifier diode?A rectifier diode is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC).   3. What is the function of diode in rectifier circuit?A characteristic of diodes is that current flows (forward direction) or current does not flow (reverse direction) depending on the direction of applied voltage. This works to convert alternating current (AC) voltage to direct current (DC).   4. Which is used as rectifier?We know that the core use of rectifier is to convert AC current into DC current. The rectifier consists of semiconductor diodes to do this function.   5. What is the limitation of a diode rectifier?Disadvantages of Full Wave Bridge RectifierIt needs four diodes. The circuit is not suitable when a small voltage is required to be rectified. It is because, in this case, the two diodes are connected in series and offer double voltage drop due to their internal resistance.   6. What is the ideal rectifier diode efficiency?It is the ratio of DC output power to the AC input power. The rectifier efficiency of a full-wave rectifier is 81.2%.   7. What is a fast recovery rectifier?Definition: Fast Recovery Diode is a semiconductor device which possesses short reverse recovery time for rectification purpose at high frequency. A quick recovery time is crucial for rectification of high-frequency AC signal. Diodes are mostly used in rectifiers because they possess ultra-high switching speed.   8. Which diode is fast recovery diode?FRD stands for fast recovery diodes. They offer high-speed support and generally have a trr of approximately 50 to 100 ns. With a VF of approximately 1.5V, it is rather large when compared to general rectifying diodes. Another generic term for the FRD type would be a “High-speed Diode.”   9. What is ultra fast recovery diode?A fast diode is a faster-than-standard current rectifier. ... A fast rectifier typically recovers ten times faster than a standard rectifier, and an ultrafast designation is usually applied to rectifiers designed to beat the standard rectifier recovery by being more than fifty times faster.   10. What is the difference between a Schottky diode and a rectifier diode?Schottky diode, also known as barrier diode is mainly used in low voltage circuits because the forward voltage drop of Schottky diode(Vf) is less than a rectifier diode. The forward voltage drop of a Schottky diode is typically in the range of . 25 to 0.5 V whereas the Vf of a rectifier diode is around 0.7 volts.   11. What is Schottky barrier rectifier?The Schottky diode or Schottky Barrier Rectifier is named after the German physicist Walter H. Schottky, is a semiconductor diode designed with a metal by the semiconductor junction. It has a low-forward voltage drop and a very rapid switching act. ... Actually, it is one of the oldest semiconductor devices in reality.

Ⅰ Introduction   One type of primary capacitor is the variable capacitor. Capacitors are classified into two types based on their capacitance. These are known as 'Fixed Capacitors' and 'Variable Capacitors.' Capacitors with a fixed capacitance value are referred to as 'Fixed Capacitors.' Similarly, capacitors with varying capacitance are referred to as Variable Capacitors.   What is a variable capacitor diode – how does it work? | Intermediate Electronics     This type of capacitor has the competence to change the capacitance values "Electrically" or "Mechanically." Variable Capacitors, unlike Fixed Capacitors, provide specific ranges of values rather than deciding the values during manufacturing. These capacitors are chosen based on the required values. This type of capacitor is preferred in the majority of Tuning Circuits.     Catalog Ⅰ Introduction Ⅱ What is a Variable Capacitor? Ⅲ Construction of Variable Capacitor 3.1 Summery Ⅳ Types  of Variable Capacitors 4.1 Tuning Capacitors 4.2 Common problems in turning circuits 4.3 Trimmer Capacitors 4.4 Mechanical Capacitors 4.5 Electronic Capacitors Ⅴ Working principle of Variable Capacitors 5.1 Turning types 5.2 Ceramic trimmers 5.3 Plastic foil types Ⅵ Variable Capacitor Applications Ⅶ FAQ     Ⅱ What is a Variable Capacitor?   Figure1:Variable Capacitor Symbol       Ⅲ Construction of Variable Capacitor   The variable capacitor's construction is shown below. As their simple construction, these capacitors are commonly used in a variety of applications. These capacitors are typically constructed with two sets of hemispherical metal plates separated by air gaps. One set of metal plates is fixed, while the other is connected to a shaft, allowing the user to turn the assembly and change the capacitance as needed. As a result, the construction of each type of capacitor differs.   Figure2: construction-of-variable-capacitor     The working principle of a basic capacitor can be applied to design this capacitor. The conductive plates of this capacitor are arranged in parallel and separated by dielectric coatings made of various materials such as reinforced paper, mica, or certain types of ceramics. These capacitors, unlike traditional fixed capacitors, are designed to change capacitance levels. In most cases, we can gain variable capacitance by varying the distance between parallel plates within a capacitor.     3.1 Summery This capacitor is built by inserting metal plates into it.Some of them are 'Fixed Plates,' while the rest are 'Movable Plates.'The area between the Fixed and the movable plates changes as a consequence of the rotation of the movable plates.Each type of capacitor in this category is built uniquely.     Ⅳ Types  of Variable Capacitors   In the market, there are two types of variable capacitors, which are as follows. The capacitance of the following capacitors can be changed manually with screwdrivers; otherwise, any device can be used.   Tuning CapacitorsTrimmer CapacitorsMechanical CapacitorsElectronic Capacitors     4.1 Tuning Capacitors   Tuning capacitors can be designed with the help of a frame. This frame has both a stator and a rotor. The frame of the capacitor can support both the mica material and the stator. When the stator is turned off, the rotors begin to rotate with the assistance of a shaft. When the movable rotor plates enter the immobile stator, the capacitance value is maximum; otherwise, it is minimum. These capacitors can provide capacitance values ranging from picofarads to tens of picofarads. Figure3:Tuning Capacitors     These capacitors are used in radio receivers with LC circuits. Tuning condensers is another name for these capacitors.       4.2 Common problems in turning circuits Variable capacitors used in tuning circuits can cause several issues. The main issue with the older types is a bend in the plates, which causes the component to short and thus become inoperative. As shown in Figure 1, this short can be detected.   Figure 4 - Testing a variable capacitor with a multimeter.     There must be no indication of low resistances around the entire turn of the variable capacitor. In good condition, the meter's needle should remain on infinite to a variable. If a short is discovered between the plates, the first step should be to attempt to correct the alignment of these plates using the screw that exists in the mobile variable axis. It is possible to adjust the plates if they are bent by pressing and releasing this screw. If the plates are bent, the technician can attempt to correct the defect very carefully, always performing a continuity test to detect the moment when the component is recovered. The insulating sheets inside them may have a small variable short problem. By carefully dismantling the component, you can obtain the defective sheets and attempt to correct the defect, or with insulating use of other variables abandoned by the same problem, or even with the improvisation of insulating sheets. Figure 5 depicts how the metal plates are arranged, with an insulating foil sandwiched between them to prevent contact between the mobile and fixed assemblies.     Figure 5 - Construction of a variable with plastic insulation.     After reassembly, an isolation test should be carried out to ensure that the short between the plates was indeed removed. If the problem is moisture or dirt, the variable can be disassembled for cleaning, but be careful not to bend plates and remember to reassemble any insulating sheet.       4.3 Trimmer Capacitors   Trimmer capacitors are used to provide basic calibration of equipment during manufacturing or servicing. These capacitors are frequently arranged on the printed circuit board in such a way that the user does not have access to change them. As a result, these capacitors are inexpensive. These capacitors are used in circuits to set the oscillator frequency, rise, latencies, and fall times. These capacitors enable servicemen to adjust devices as needed. These capacitors are classified into two types: air trimmer and ceramic trimmer.   There are three leads in this capacitor. The first lead is connected to the immobile part, the second to the rotary, and the third to the common. The purpose of a semi-circle-shaped movable disc is to observe the movement of this capacitor. This capacitor has two plates that are separated by a dielectric material and are arranged in parallel to each other.     Figure6:Trimmer Capacitors     These capacitors can be classified based on the dielectric material used, such as air trimmer or ceramic trimmer.     4.4 Mechanical Capacitors These capacitors are made up of a series of curved plates that are connected to a knob. The main advantage of this is that the capacitance of the capacitor can be easily changed if necessary. Mechanically, these are dependable because they are not overly complicated.     4.5 Electronic Capacitors By applying a DC voltage to these capacitors, you can change their capacitance. These capacitors' main applications are multimeters, resistance, and amperage. The DC (direct current) here refers to the type of current supplied by a battery.       Ⅴ Working principle of Variable Capacitors   The capacitance can be varied between a minimum and a maximum value using an electrode system composed of one fixed and one movable part – stator and rotor. The temperature coefficient (TC) for the various dielectrics has a great difference from the corresponding values for fixed capacitors. Except for the best precision components, the variations are significantly larger, which has to do with the mechanical conditions as well as the entire construction. Trimmer capacitors are primarily used on printed circuit boards (PCBs), but surface mount designs are becoming increasingly popular. Trimmers frequently have friction, which increases the turning moment and, as a result, locks the capacitor in its adjusted position.     5.1 Turning types   Air dielectric As shown in Figure 7, the classic variable capacitor is be composed of semicircular electrodes that can be turned into each other. The styles are designed for either PCB or panel mounting. They are mainly used for tuning resonance circuits.   Figure7: A variable air-insulated capacitor schematic and an example of Tronser's design.     Mechanical precision is required due to the air-insulated electrodes. The plate distance is usually between 0.2 and 1 mm. The cost is fairly high.     5.2 Ceramic trimmers We can make a ceramic trimmer capacitor by reducing the plates in Figure 7 to just one silver-plated ceramic rotor that is turned in over the stator electrode. Figure C5-2 depicts an example of this design. There are also multilayer designs. The capacitors are available in both hole mount and surface mount configurations.Because Type 1 ceramics are used, losses will be minimal.     Figure 8: Explanatory sketch of a cross-cut using a ceramic trimmer.       5.3 Plastic foil types If we replace the air insulation in Figure 7 with some plastic foil, the electrode distance can be reduced while the r – and thus the capacitance – increases, albeit at the expense of a slightly lower Q value. Low loss plastics such as Teflon (PTFE), polypropylene (PP), and polycarbonate (PC) are common, but polyester (PETP) is also available.       Ⅵ Variable Capacitor Applications         Ⅶ FAQ   1). What is the main function of the variable capacitor? It is used to fix the resonant frequency in the LC circuit.   2). How these capacitors are made? These are made with two sets of curved metal plates and they are divided by air gaps   3). What is a ganged capacitor? The combination of two capacitors that are connected together is known as a ganged capacitor.   4). What are the two types of variable capacitors? They are tuning capacitors and trimming capacitors.   5). What is the capacitance values of a variable capacitor? Typically ranges from 100pF to 500pF   Thus, this is all about variable capacitors and the characteristics of the variable capacitor mainly include accuracy, tolerance, polarity, voltage rating, and capacitance range. Here is a question for you, what are the advantages of a variable capacitor?

IntroductionIn the landscape of modern electronics in 2025, the Zener diode remains a fundamental component for voltage stabilization and reference. Unlike standard diodes, Zener diodes are engineered to operate in the reverse breakdown region. By utilizing the specific breakdown voltage of the PN junction, they maintain a constant voltage across their terminals even when the current varies significantly.Zener diodes serve critical roles as voltage regulators, surge suppressors, and reference elements in power supply circuits. Given their importance, proper maintenance and accurate fault detection are essential skills for technicians and engineers. This guide details how to detect, test, and distinguish Zener diodes using modern troubleshooting techniques.Ⅰ How to Test Zener Diodes with Three Methods?1.1 Resistance Measurement (Basic Health Check)The resistance measurement method describes the basic health of the component—specifically, checking for shorts or open circuits. While modern digital multimeters (DMMs) are standard in 2025, analog multimeters can still be useful for this specific test due to their load characteristics.The Principle: Using an analog multimeter set to the Rx10K block (which typically uses an internal 9V or 15V battery), you can bias the PN junction.Forward Bias: Connect the red probe (negative in analog meters) to the Anode and black to the Cathode. You should see low resistance.Reverse Bias: Connect in reverse. Ideally, the resistance should be high. However, if the battery voltage exceeds the Zener voltage (e.g., a 5V Zener tested with a 9V internal battery), you will measure a resistance drop, indicating the Zener is functioning (breaking down) correctly.Using a Digital Multimeter: Set the meter to Diode Mode. Touch the probes to the diode. In one direction (forward bias), you should see a voltage drop between 0.6V and 0.8V. In the reverse direction, it should show "OL" (Open Loop) unless the Zener voltage is lower than the meter's test voltage (rare in modern DMMs). If you read 0.000V in both directions, the diode is shorted.1.2 Voltage Measurement (The Most Accurate Method)To determine the exact Zener voltage (Vz), testing the component "live" or in a test circuit is required. This is the professional standard for verifying if a Zener diode is drifting or operating within tolerance.Procedure:Connect a DC Power Supply in series with a current-limiting resistor (e.g., 1kΩ to 10kΩ) and the Zener diode (Reverse Biased).Set the power supply voltage higher than the expected Zener voltage.Use a digital multimeter in DC Voltage mode to measure across the Zener diode.Result: If the reading matches the component's rated voltage (e.g., 5.1V, 12V), the diode is healthy. If the voltage fluctuates significantly or equals the input voltage, the diode is faulty.1.3 Measuring High-Voltage Zeners (Insulation Tester)For industrial Zener diodes with high regulation voltages (above 20V or 50V), a standard multimeter's test voltage is insufficient. In these cases, a Megger (Insulation Resistance Tester) or a high-voltage DC supply can be used.Method: Connect the Megger leads to the diode (reversed). Slowly generate voltage. When the resistance reading stabilizes at a specific voltage drop, that represents the Zener breakdown voltage. Warning: Ensure the current is limited to prevent destroying the device, as Meggers can output high voltages meant for insulation testing, not semiconductor characterizing.Figure 1. Standard Zener Diode SymbolⅡ How to Measure the Leakage of Zener Diode?Leakage current is a silent killer in precision circuits. A Zener diode might pass a basic voltage test but fail under load or temperature changes due to excessive leakage.Advanced Testing: A standard multimeter cannot effectively detect minor leakage. Instead, use a Curve Tracer or an Oscilloscope with a component tester function. By applying a reverse voltage gradually, you monitor the current. A healthy Zener should conduct negligible current until it hits the "Knee Voltage." If the current rises linearly before the breakdown voltage, the diode is "leaky" (soft breakdown) and should be replaced.Ⅲ How to Figure the Polarity of the Zener Diode?Correct installation is vital. Here is how to identify the Anode (+) and Cathode (-):Visual Inspection (Through-Hole): Look for the black or blue band on the glass/plastic body. This band indicates the Cathode (-) side.Visual Inspection (SMD): On Surface Mount Devices, the Cathode is usually marked with a white bar or a chamfered edge.Multimeter Test: Set to Diode Mode. Place probes on terminals. The orientation that gives a reading (approx 0.7V) indicates the Red probe is on the Anode and the Black probe is on the Cathode.Figure 2. Zener Diode Regulator ConfigurationⅣ How to Identify Color Code Zener Diode?While many modern diodes have the part number printed directly (e.g., "5V1" or "1N4733"), older glass-passivated diodes use color bands similar to resistors.The color bands typically represent the JEDEC type number (e.g., 1Nxxxx). Alternatively, in the European BZX series, bands may denote voltage: Example: A diode with Brown (1) and Red (2) bands might represent 12V (depending on the specific manufacturer coding system). Always cross-reference with a datasheet or use a modern SMD/Component Tester (LCR Meter) to verify the breakdown voltage automatically.Ⅴ How to Distinguish Zener Diodes and Ordinary Diodes?Physically, Zener diodes and standard signal diodes (like the 1N4148) often look identical (small, glass, orange/red body with a black band).The Distinction Test: The defining characteristic is the Reverse Breakdown Voltage.Standard Diode: Will block reverse voltage up to very high limits (e.g., 100V+). Under a 12V reverse test, it acts as an Open Circuit.Zener Diode: Will conduct current when the reverse voltage exceeds its rating (e.g., 5.1V).Practical Trick: Apply 12V DC via a 1kΩ resistor to the diode in reverse. Measure the voltage across the diode. If it reads ~12V, it is likely a standard diode. If it reads a lower, stable voltage (e.g., 5.1V, 9.1V), it is a Zener Diode.Figure 3. Zener Diode Voltage Regulator CircuitⅥ FAQ1. How do you identify a 12V Zener diode?The most reliable method is to place the diode in a reverse-biased circuit with a power supply set to roughly 15V-20V and a series resistor. If the voltage across the diode clamps and stabilizes at approximately 12V, it is a 12V Zener. If you use a standard multimeter diode test, it will only show the forward voltage drop (~0.7V), which does not reveal the Zener voltage.2. How do you know if a Zener diode is bad?Common Failure Signs:Short Circuit: Reading 0Ω or 0V in both directions (most common failure).Open Circuit: Reading "OL" in both directions.Drift: The diode regulates voltage, but at the wrong value (e.g., a 5V Zener regulating at 3V or 8V).3. What is the difference between a rectifier diode and a Zener diode?A standard rectifier diode is designed to conduct current in only one direction (Forward Bias) and block voltage in the reverse direction. A Zener diode is designed to conduct in the forward direction like a normal diode, but also safely conduct in the reverse direction once a specific voltage threshold (Zener Voltage) is reached.4. What happens when a Zener diode is shorted?When a Zener diode fails short, it acts like a straight piece of wire. It allows maximum current to flow in both directions with zero resistance. In a power supply circuit, this usually causes the fuse to blow or the series resistor to overheat and burn out immediately.5. Can I test a Zener diode in-circuit?In-circuit testing is often inaccurate due to parallel components (capacitors or other resistors) affecting the reading. However, you can check for a dead short. If you measure 0Ω across the Zener while it is on the board, it is likely dead. For accurate voltage testing, lift one leg of the component off the PCB.6. Why is a Zener diode used in reverse bias?Zener diodes are heavily doped. This doping creates a very thin depletion region that allows electrons to tunnel across the junction when a specific reverse voltage is applied (Zener Effect). This property is what provides the stable reference voltage required for regulation.7. What happens if you forward bias a Zener diode?If you connect a Zener diode in forward bias (Anode to Positive), it behaves exactly like a standard silicon diode. It will conduct current with a voltage drop of approximately 0.7V. It does not provide voltage regulation in this orientation.8. How do I identify an SMD Zener diode?SMD (Surface Mount Device) Zeners are often too small for full part numbers. They use Marking Codes (typically 2 or 3 alphanumeric characters). You must look up this code in an "SMD Codebook" or datasheet to identify the voltage rating. Visually, they often come in SOT-23 (3-leg) or SOD-123 (2-leg) packages with a band marking the cathode.

Introduction As we all know, Resistors play a important role in limiting current in the circuit. Among then, pull-up resistors and pull-down resistors are often mentioned and frequently used in electronics. The pull-up is to clamp the uncertain signal to a high logical level through a resistor, which acts as a current limiter; while the pull-down resistor clamps the uncertain signal to a low logical level. Because there are only two states of high level and low level in digital circuits, it is uncertain at the initial stage of digital signals. Pull-up/ Pull-down Resistor - Explained ( with calculation ) Catalog Introduction Ⅰ Why Pull-down and Pull-up Resistor? Ⅱ Pull-up & Pull-down Resistor Circuits Ⅲ What the Role of Pull-up and Pull-down Resistor? Ⅳ Pull-up & Pull-down Resistor Applications Ⅴ How to Select Pull-up & Pull-down Resistors? Ⅵ FAQ Ⅰ Why Pull-down and Pull-up Resistor? Pull-up and pull-down resistors are often applied when interfacing a switch or some other input with a microcontroller or other digital gates. That is, in the initial stage of digital circuit power-on, because the high logical level and low level of the output state are uncertain, in order to make the circuit state normally, a pull-up resistor or pull-down resistor is needed to stabilize the uncertain circuit state. The low logical level is connected to GND inside the IC, and the high level is connected to the super resistance inside the IC.The pull-up resistor connects with the status port of the power supply. Simply put, the high voltage is applied to this point, where the potential will increase. The pull-down resistor means that the resistor is connected to the negative pole, and there is also the case of digital grounding. When the input port signal changes due to different circuit forms, the change will be fed back to the output port, so that the output port acquires a state that should have been completed, but the input port has no signal at this time and keep the original state.According to the above understanding, many people may feel awkward. Take an example from daily life, when you use the key to open the door, people enter but the door is not closed, at this time, you can add a switch to make the door close automatically. Figure 1. Schematic of Pull-up Resistor at Positive Input The above schematic diagram explains why the positive pole and the input terminal resistor can high the level. The two resistances of the port are assumed to be equivalent. We can get that the voltage of the port is 2.5V according to Ohm's law. By connecting the pull-up resistor (red part), the voltage of the port rises at this time, calculate the port voltage. Among them, 10K is connected in parallel with the later connected 1K, and the resistance must be greater than or equal to 1K, which is equivalent to the series relationship between 1K and the 10K resistor below, but the passing current is actually the same. Finally, the voltage of the two 10K resistors increases, and the terminal voltage also increases.The pin connected to the IC and power (or ground) is not necessarily a pull-down resistor. When this happens, many people may think that the red part of the figure is also a pull-down resistor. However, it is not connected in series with any pin or ground. In fact, it is used for circuit startup resistor, not pull-up/pull-down resistor. For the pull-up/pull-down resistors, it is only for the input port and the output port. Although some circuits will connect the pull-up and pull-down resistors to the redundant ports for stability, not all the resistors are connected to one pin of the IC all the time, and the other pin is connected to power or ground to represent the pull-up and pull-down resistors.   Ⅱ Pull-up & Pull-down Resistor Circuits Look at the following analyses to figure out what are pull-up resistor and pull-down resistor in circuits. Pull-up resistors are used to ensure that a wire is pulled to a high logical level in the absence of an input, while pull-down resistors ensure the voltage between VCC and a microcontroller pin is actively controlled. Just check the details below. Figure 2. OC(TTL) Circuit，OD(COMS) Circuit When the I/O port of the IC is in high level, the impedance between the node and GND is very large, which can be understood as infinite. At this time, it is connected to VCC through a pull-up resistor (such as 4.7K ohm, 10K ohm resistor), and the voltage divider of the pull-up resistor is almost negligible. When the I/O port node is in low level, it can be directly connected to GND. At this time, VCC and GND are connected through the pull-up resistor, and the current passing through is very small, which can be ignored.The level value are relative to the ground level, so you should refer to the ground level value. See if those pins are connected to the ground, it has nothing to do with whether they are connected to peripheral devices.Connect a 10K ohm or 4.7K ohm pull-up resistor between the node and +5V to pull up the potential of this node. Often this node requires a single-chip microcomputer or other controller to control it (and this node is connected to I/O). If you simply want to make this node a high level, and the output impedance is very large, you can directly connect the power supply, but if the microcontroller wants to make this node low, that is, the node is grounded inside the microcontroller, so that the 5V power supply and the ground are short-circuited.In addition, when this node is required to be at a high level, the impedance between this node and the ground is generally very large. For example, with an impedance of 100K ohms, when connect a 10K ohm pull-up resistor, the voltage at this point is 100KΩ/(100K +10K)*5V=4.5V, so it can also get a high level.When the node is required to be low level, just connect it to the ground, and there is a 10K resistor between the power supply and the ground, so that it will not be short-circuited. When it is low, there is a loop formed by a load between the power supply and the ground. Sometimes this node will be connected with a resistor in series. Because the current flows to the place with low impedance, the current will flow to the ground through the resistor connected to the power supply instead of Flow to this resistance connected to the node, because the resistor connected to this node has a high impedance, so the potential at this point is in low level.It can be considered that, for the I/O port of the IC, controlling the high and low levels inside the IC is equivalent to controlling the O/O port to be connected to its internal GND or a very large resistor, such as 100K ohms. When the I/O port is the low level (0V), inside the IC, the pin that controls the O/O port of the IC chip is connected to GND.When the I/O port is at a high level, such as 5V, the I/O port pin is connected to a very large resistor in the chip, such as 100K ohms, and sometimes another one is connected in series at the I/O node. A resistor with a small resistance value, such as 68 ohms, because the current flows to a place with low impedance, when the I/O port and GND inside the chip are connected to a low level, the pull-up resistor and the GND inside the chip form a loop.At this time, the current at the I/O port node will flow to the GND inside the chip, because a small resistance resistor is connected in series at the node, which is high resistance relative to GND, so the current will not flow through this series resistor.Using a pull-down resistor, when the I/O port is in a high-impedance state, the pull-up resistor can keep it in a high-level state. That is, when the I/O port is in the high-impedance state, using a pull-down resistor to connect this port to GND. The high-impedance state has a large resistance value, which can be understood as disconnection, in fact, it is actually a large resistor inside the chip. The resistors are connected and pulled to the ground, so there is no current and the level value is 0. It can only work unless a high level value is given to this pin. Figure 3. Pull-up and Pull-down Resistor in MCU   Ⅲ What the Role of Pull-up and Pull-down Resistor? As for the purpose of pull-up & pull-down resistors, generally speaking, the pull-up resistor increases the current, and the pull-down resistor is used to absorb the current.1) Increase the voltage level.When the TTL circuit drives the CMOS circuit, if the output high level of the TTL circuit is lower than the lowest high level of the CMOS circuit, then it is necessary to connect a pull-up resistor to the output terminal of the TTL to increase the value of the output high level. The OC gate circuit must add a pull-up resistor to increase the high-level value of the output.2) Increase the drive capability of the output pin.In order to enhance the drive capability of the output pins, pull-up resistors are often used on some single-chip pins.3) The N/A pin (the pin not connected) should be anti-static and anti-interference.On the CMOS chip, in order to prevent damage caused by static electricity, the unused pins cannot be left floating. Generally, a pull-up resistor is connected to reduce the input impedance, provide a leakage path, and improve the anti-electromagnetic interference ability of the bus. Because the pin is left floating, it is easier to receive electromagnetic interference from the outside world.4) Resistance matchIn the long-line transmission, the resistance mismatch can easily cause the reflected wave interference. In addition, the pull-down resistor makes the resistance match, which can effectively suppress the reflected wave interference.5) Preset space state/default potentialPull-up or pull-down resistors are connected to some CMOS input terminals to preset the default potential. When these pins are not used, these input terminals are pulled down to low level or pulled up to high level. The state when idle on the bus such as I2C is obtained by the pull-up and pull-down resistors.6) Improve the noise tolerance of the chip input signal.If the input terminal is in a high-impedance state, or in a floating state, a pull-down or pull-down resistor needs to be added at this time, so as to avoid the random level. Similarly, if the output terminal is in a passive state, a pull-down or pull-down resistor needs to be added. For example, the output terminal is only the collector of a transistor, thereby improving the noise tolerance of the chip input signal and enhancing the anti-interference ability through a pull-up resistor or pull-down resistor. Figure 4. Pull-up/ Pull-down Resistor   Ⅳ Pull-up & Pull-down Resistor Applications When to use pull-up or pull-down resistors? Look at the following cases explained.1) If a pull-up & pull-down resistor is used for the input signal pin, the usual function is clamping the signal to a certain level to prevent the signal line from appearing in an uncertain state. In practical applications, the 10K ohm resistor is the most used pull-up resistor. Whether to use a pull-up resistor or a pull-down resistor depends mainly on the needs of the circuit system itself. For example, for a highly effective enable control signal, we hope that the circuit system be in an invalid state after power-on, and then a pull-down resistor will be used.Assuming that the enable signal is used to control the motor, if it is left floating, the signal line may be triggered falsely to a high level by other noise interference after power-on (or during operation), resulting in undesired rotation of the motor, and a pull-down resistor can be added at this time. Correspondingly, for the active-low reset control signal (RST#), if we want to be in an inactive state after power-on reset, a pull-up resistor should be used.2) Most chips with logic control functions (such as single-chip microcomputers, FPGAs, etc.) will integrate pull-up or pull-down resistors. Users can choose whether to turn on or not according to their needs. STM32 microcontroller GPIO mode includes pull-up or pull-down.3) According to the resistance value of the pull-up resistor, we can also divide it into strong or weak pull-up/down. The pull-up resistors integrated in the chip are usually weak pull-up (larger resistance), the smaller the pull-up resistance, the stronger the level capability (strong pull), and the stronger the ability to resist external noise (that is, if the unwanted interference noise is to change the strong pull signal level, the required energy must be strengthened accordingly ), but the smaller the pull-up resistance, the greater the corresponding power consumption, because the normal signal requires more energy to change the state of the signal line. In terms of energy consumption, both pull-up /down resistors are the same.4) There is no strict definition of how many ohms are the boundary between strong pull and weak pull. Generally, the pull-up resistors we use are weak pulls, so we can still use external control signals to pull up/down the signal lines as needed.The extreme of the strong pull resistance is the zero, that is, the signal line can directly connected to the power supply or ground.5) There are more knowledge points involved when the pull-up resistor is used as an output (or input and output), but the essential function is also to clamp the level. The most common output pull-up resistor appears in the open collector (OC) Or open drain (OD) structure pin.6) The current sink capability and current source capability are also called the drive capability of the chip pins. For any given chip, the pin drive capability is limited. If the load driven by the pin is large, it may cause the output level to be incorrect (the predetermined level cannot be output).7) OC (OD) pin output structure is different (OC structure exists in the transistor, and OD structure exists in the field effect transistor FET). The output of most comparator chips is an OD/OC output structure, and the signal pins of many chips or modules that feed back the system status are also in this structure, so that users can pull up the level to the corresponding level according to the actual needs of the circuit system. With the power supply voltage VCC, the level conversion can be omitted. Figure 5. Pull up Resistor with Example   Ⅴ How to Select Pull-up & Pull-down Resistor? When select pull-up & pull-down resistors, you can consider the following three aspects:1) Considering power saving, sink current capability of the chip should be large enough, the resistance is large and the current is small.2) It is necessary to ensure sufficient drive current, so the resistance is small and the current is large.3) For high-speed circuits, excessive pull-up resistors may have smooth edges.Considering the above three points comprehensively, the resistance value is usually selected between 1K and 10K. The same principle applies to pull-down resistors.   Ⅵ FAQ 1. What is pull-down and pull-up resistor?A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.   2. What is difference between pull up and pull-down resistor?A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.   3. When to use pull-up or pull-down resistors?Pull-up and pull-down resistors are often used when interfacing a switch or some other input with a microcontroller or other digital gates. Most microcontrollers have built-in programmable pull-up and/or pull-down resistors, so fewer external components are needed.   4. What is the function of a pull-up resistor?In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC.   5. What is the purpose of pull-down resistor?What is Pull-down Resistors. Similarly to pull-up resistors, pull-down resistors ensure the voltage between VCC and a microcontroller pin is actively controlled when the switch is open. However, instead of pulling a pin to a high value, such resistors pull the pin to a low valued instead.   6. How do you calculate pull-down resistors?To calculate the pull-down resistor value, it's slightly different from the pull-up resistor value. Knowing that current is 100uA, we'll take 0.5v as our pull-down voltage since the input is 0.8v. Thus, applying our R = V/I once again, but this time we don't have to minus, so our formula remains constant.   7. Why does I2C need pull-up resistor?As discussed in the I2C Basics module, the resistors that are commonly seen on I2C circuits sitting between the SCL and SDA lines and the voltage source are called pull up resistors. ... A pull up resistor is used to provide a default state for a signal line or general purpose input/ouput (GPIO) pin.   8. Which port has no built in pull-up resistor?Input/Output (I/O) pin − All the circuits within the microcontroller must be connected to one of its pins except P0 port because it does not have pull-up resistors built-in.   9. What is pull up and pull down in Arduino?Introduction: Understanding the Pull-up/Pull-down Resistors With Arduino. ... With a pull-up resistor and with the button unpressed you make a logic state ON and with the button pressed you make a logic OFF. With a pull - down resistor and a pressed button you make an ON logic state and OFF logic state when its unpressed.   10. What happens if the pull up resistor for an I2C signal is too small?Too small of a value will once again prevent the output drivers from sinking enough current to pull the pin all the way down to 0.

Introduction A resistor is a passive two-terminal electrical component. After it is connected to the circuit, the resistance is fixed, which can limit the current through the branch connected to it. On one hand, the resistance that cannot be changed is called a fixed resistor, on the other hand, the resistances of potentiometers or variable resistors are changeable. The main physical characteristic of a resistor is to transform electrical energy into thermal energy. It can also be said that it is an energy-consuming element, because internal energy is generated when current passes through it. Figure 1. Use Resistor in Circuit Catalog Introduction Ⅰ Functions of Resistor Ⅱ Three Basic Principles for Resistor Selection Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? 3.2 Pull-down Resistor in Transistor Circuits Ⅳ FAQ Ⅰ Functions of Resistor In short, the function of resistance is to limit current, divide current, divide voltage, and convert electric energy into internal energy (heating) in the circuit. According to Ohm's law, through calculations, resistors in parallel and series connections can be used to achieve the desired current and voltage. Also there are different resistors and switches combined to produce voice-activated switches, photosensitive switches, infrared switches and so on. How to Use Resistors in circuits? 1) Limit CurrentIn order to prevent the components connected in series from being burnt out by the excessive current and to ensure the normal operation of the electrical appliances, a variable resistor can usually be connected in series in the circuit.2) Current DiversionThe resistor is connected in parallel to the component or circuit that needs to be shunted, and the voltage does not change. The function of this resistor is to divide current.3) Voltage DiversionGenerally, electrical appliances are marked with a rated voltage value. If the power supply is higher than it, the electrical appliance cannot be directly connected to the power supply for a normal operation. In this case, a resistor with suitable resistance can be connected in series in the circuit to share a part of the voltage, therefore the electrical appliance can work at the rated voltage. At this time, the role of the resistor is to divide the voltage.4) Provide Bias VoltageIn the transistor circuit, the resistor is connected between the base of it and the working voltage. At this time, the power supply provides a bias voltage to the base through the resistor, and the resistance can determine the bias voltage. The role of the resistor in the circuit at this time is to provide a bias voltage.5) Negative FeedbackUsed in the resistance between the base and collector of the transistor, then the feedback branch of the negative feedback circuit is formed in the circuit. At this time, the resistor plays a negative feedback role in the circuit.6) OscillationResistor and capacitor form an RC circuit, which can be combined in parallel and in series.7) Damping EffectConnecting a resistor in parallel in the LC resonant circuit can reduce the Q value, at this time, resistor plays a damping effect.8) DecouplingThe use of resistors in multi-stage amplifier circuits can prevent harmful low-frequency interference, which play a decoupling effect.9) Convert Electrical Energy into Internal Energy (Heating)When the current passes through the resistor, it will convert all (or part) of the electrical energy into internal energy, which will generate heat. This principle is often used in electric stoves and heaters in our lives.10) Convert Current into VoltageWhen current flows through the resistor, a voltage will be generated across the resistor. As shown in the figure below, the collector load resistor R2 plays this role, converting the current flowing through the resistor R2 into a voltage and outputting it from U0. Figure 2. Resistor Circuit   Ⅱ Three Basic Principles for Resistor Selection 1) Choose resistors that are manufactured by a certification body that implement high-level standards.2) Choose resistors produced by manufacturers with functional advantages, quality advantages, efficiency advantages, price advantages, and service advantages.3) Choose a manufacturer that can meet the above-mentioned requirements in the model catalog.   Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? First of all, we must understand the basic principle of the transistor. It is a current-controlled element, which is different from the MOFET, a voltage-controlled element. The transistor has three working areas: cut-off area, amplification area and saturation area. Take NPN transistor as an example, the voltage difference（UBE）of BE is about 0.6V (the actual size depends on the model of the component). When UBE＜0.6V , the transistor is off; when UBE=0.6V, the transistor is in the amplification or saturation region. Figure 3. Schematic Diagram of the NPN Transistor Current When the transistor is in the amplification area, the added resistance between the base and VCC is a bias resistance. The following explains why the base should be added when the transistor is used as a switch. What is the difference between transistor and MOSFET circuits when adding a resistor.The following figure is the most commonly used circuit diagram of NPN transistors. The common input terminal is the I/O port of the microprocessor (microcontroller, DSP, ARM, etc.). Figure 4.  NPN Transistor Take the microcontroller I/O port with 0/5V input as an example. Why must a resistor be connected in series with the base? Can it work without a resistor? Here the resistor is a current control element. When the transistor is in an amplified or saturated state, the voltage of the UBE is 0.6V, and the base current can be calculated according to the input voltage U. The calculation formula is Ib=(U-0.6 )/R1. It can also be seen from the formula that if the current limiting resistor R1 is not connected, when the input voltage is greater than 0.6V, the base current will be very large to burn the tube.Moreover, the resistor cannot be used casually. It needs to be calculated according to the input voltage and the characteristics of the tube. For example, the amplification factor β of the transistor is 50, the maximum current of the collector is 500mA, and the input voltage is 5V. If the design requires the transistor to be in a saturated state, then Ic=500mA, Ib=Ic/β=10M=mA, where the current-limiting resistance R1=(5V-0.6V)/Ib=430Ω. If it is required to input 5V, the collector current is about 200mA, then Ib=Ic/β=200mA/50=4mA can be calculated, finally the current-limiting resistance R1=(5V-0.6V)/Ib=1075Ω (1K can be selected Standard resistance). Note: The above figure is used to explain the example, but it is not very reliable. A more reliable connection method should be to connect a large resistor (such as 10K, or 20K) between the base and the ground. When there is no input, pull the base down quickly to ensure that the tube is in a stable cut-off state.If the NPN transistor in the figure above is replaced with an N-channel MOS tube, the principle is the same. When a high level is input, the tube is turned on, and when a low level is input, the tube is turned off. Figure 5. MOSFET Circuit Since the MOSFET is a voltage-controlled device, the current of the gate (G) is very small and can be ignored, so it can work normally without connecting the resistor R1.The figure after remove the resistor is shown in the below: Figure 6. MOSFET Circuit without Resistor Note: In actual applications, a resistor is generally connected in series to improve reliability. The product reliability is very important. Without current-limiting resistor, when the MOS is   damaged by voltage breakdown, the components on the control terminal will be affected easily, especially the processor, is easily damaged by high current. 3.2 Pull-down Resistor in Transistor Circuits 🔺For TransistorsThe transistor is a current-type driving component, so a current-limiting resistor is connected to the base, generally less than 10K, and the typical values are 3.3K, 4.7K, 5.1K, 6.8K, etc. What is the function of this pull-down resistor?The following figure shows the transistor 8050 switching circuit. The transistor will be turned on when the I/O port outputs a high level, and the transistor will not be turned on. If the I/O port does not output a high level, the base will always be pulled low without a 68K pull-down resistor, that is to say it is in the cut-off state. The circuit may be in an unstable state, especially when it is initialized at the moment of power-on. It is easy to generate noise and easily cause the transistor to malfunction, especially for some general input/output ports. Therefore, this resistor is actually a bias resistor, which makes the base to be pulled down when there is no driving signal, making the circuit more reliable. Figure 7.  Pull-down Resistor in Transistor Circuit Although the pull-down resistor can make the circuit more reliable, tit cannot be too large or too small. If the resistance too large, the base current will not be enough to drive the transistor. On the contrary, if it is too small, the bias voltage will be less than the transistor conduction voltage. In general, this resistance is not more than 100K.Sometimes we see that a capacitor is connected in parallel with this resistor. In fact, this is generally designed in high-speed signal switching circuits. Adding a capacitor can improve performance, as shown below: Figure 8.  RC Circuit 🔺For MOSFETUnlike transistors, MOS transistors are voltage-controlled components, which are driven by voltage. We all know that there is parasitic capacitance between the two pins of MOS transistors. In fact, the key of MOS transistors’ conduction is the charging and discharging of capacitors. Therefore, for the N-type MOS, it will be turned on when Vgs is greater than a certain value, but for the P-type MOS, it will be turned on when the value of Vgs is less than a certain value.Therefore, due to the capacitive effect between the three pins, when the MOS is constantly turned off, the parasitic capacitance voltage can be properly discharged, which is similar to the role of a bleeder resistor and is a kind of protection for the MOS. Figure 9.  MOSFET Circuit Ⅳ FAQ 1. What is the function of the resistor?A resistor has the ability to reduce voltage and current when used in a circuit. The main function of a resistor is to limit current flow. Ohm's law tells us that an increase in a resistors value will see a decrease in current.   2. How do resistors work?A conductor has low resistance, while an insulator has much higher resistance. Devices called resistors let us introduce precisely controlled amounts of resistance into electrical circuits. ... A resistor works by converting electrical energy into heat, which is dissipated into the air.   3. Why do you need resistors?A resistor controls the flow of the electrical current within a circuit. ... Resistors are essential to many electoral circuits, and they can be applied to a myriad of different applications. Protect against voltage spikes. Resistors also protect components against voltage spikes.   4. What role do resistors play in electronic devices?A resistor is a passive two-terminal electrical device that resists the flow of current. It is probably the simplest element in an electronic circuit. It is also one of the most common components as resistance is an inherent element of nearly all electronic circuits. They are usually color-coded.   5. What is a good example of a resistor?A few examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude.   6. What happens if I use a higher ohm resistor?The cases where using a higher value resistor will damage a circuit exist, but are a bit less usual than the cases where it may simply produce a weaker result than desired, or a different frequency response than desired.   7. What is a resistor simple explanation?A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor. ... The most common type in electronic devices and systems is the carbon-composition resistor.   8. What happens when a resistor blows?Blowing Up a Resistor. By applying too high a voltage to a resistor, the resistor will draw too much current. This causes excessive power to be dissipated in the resistor which makes it go up in flames and a cloud of smoke as this video shows.   9. How is a resistor connected in a circuit?Resistors are said to be connected in “Series”, when they are daisy chained together in a single line. Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on.   10. Do resistors change voltage?The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor. Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. V = I R.