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IntroductionLED lights cannot directly use the conventional mains grid voltage, because of the characteristics of LED lighting. In order to meet the special voltage and current requirements of LEDs, a specially designed voltage conversion device must be used to make LEDs work normally. This device is an LED driver. LED drivers are usually switching mode devices that convert the input voltage (Typically 120-220 VAC or 12 VDC) into a voltage at which the current drawn by the LED's is equal to its drive current. The drive current is regulated for optimum brightness, led service life, and battery life. A drive current lower than the maximum drive current of an LED can greatly prolong service life. As a key part of LED lighting, the quality of LED drivers directly affects the performance of LED lighting.Choose the Correct LED Drivers For LED LightsNo matter how good the quality of the LED driver is, failure and maintenance are inevitable. This article will analyze the 10 failures in LED lighting design and its application based on the relevant technology and practical experience of the LED driver.CatalogIntroductionⅠ LED Driver Failure Analysis1.1 Forward Voltage Drop (Vf) Range1.2 Power Margin and Derating Requirements1.3 LED Working Characteristics1.4 Test Session1.5 Different Load with Different Test Results1.6 LED Driver Circuit Problem1.7 Wrong Phase Wring1.8 Grid Fluctuation1.9 Frequent Line Trips1.10 Drive CoolingⅡ LED Driver Maintenance2.1 Multimeter to Detect LED Driver2.2 Identify LED Power SupplyⅢ LED Driver Circuit Modulation3.1 Pulse Width Modulation (PWM)3.2 Pulse Frequency Modulation (PFM)3.3 Sliding-Mode ModulationⅣ One Question Related to LED DriverⅠ LED Driver Failure AnalysisThe LED driver is measuring current passing through LEDs using sense resistor and then increase or decrease the voltage to maintain constant current continuously. LEDs are kind of diode so they need DC voltage to operate so most of the LED drivers are boost and can vary output supply in wide range (example, 16V to 38V). They also have dimming control by PWM signal from microcontroller OR by having a manual potentiometer to change sense resistor. According to them, LED driver failures are complex, but we can follow the steps below to analyse.1.1 Forward Voltage Drop (Vf) RangeLED lamp load end is generally composed of a number of LEDs connected in series, and its working voltage Vo=Vf×Ns, where Ns represents the number of LEDs. And the Vf of an LED varies with temperature. Generally, at a constant current, Vf becomes lower at high temperatures and becomes higher at low temperatures. The LED lamp load working voltage is VoL at high temperature, and VoH represents a value at low temperature. When selecting an LED driver, consider that the driver output voltage range is greater than VoL～VoH.If the maximum output voltage of the LED driver is lower than VoH, the maximum power of the lamp may not reach the actual power required at low temperature. If the minimum voltage of the selected LED driver is higher than VoL, the output of the driver may exceed the working range at high temperature. And LED driver will work unstable, making the lights flicker.Considering the overall cost and lamp efficiency, don’t blindly pursue the ultra-wide output voltage range of the LED driver. Because the driver voltage is only in a certain range, its efficiency is the highest. When the range is exceeded, the efficiency and power factor (PF) will deteriorate. In addition, if the design of the driver output voltage range is too wide, high costs and unoptimized efficiency will be made. 1.2 Power Margin and Derating RequirementsIn general, the nominal power of the LED driver refers to the data measured under the rated environment and rated voltage. Taking into account different applications, most LED driver suppliers will provide power derating curves in their product specifications (common load vs. ambient temperature derating curves and load vs. input voltage derating curves).As shown in Figure 1, the red curve represents the power derating curve when the input is 120Vac, and its load varies with the ambient temperature. When the ambient temperature is lower than 50℃, the LED driver is allowed to be 100% full load. When the ambient temperature is as high as 70℃, the LED driver can only be derated to 60% of the load. When the ambient temperature changes between 50℃~70℃, the driver load varies with the temperature linearly.Figure 1. Power Derating Curve (Load vs Ambient Temperature)The blue curve represents the power derating curve when the input is 230Vac or 277Vac, and its load varies with the ambient temperature. The principle is similar to the above mentioning.As shown in Figure 2, the blue curve represents the derating curve of the LED driver when the ambient temperature is 55°C, its output power varies with the input voltage. When the input voltage is 140Vac, the load of the driver is allowed to be 100%, and the input voltage will be adjusted downward. If the output power remains the same, the input current will rise, resulting in input terminal loss and lower efficiency. When the device temperature rises, exceeding the rated temperature, which may cause the device to fail.Figure 2. Power Derating Curve (Load vs Input Voltage)Therefore, when the input voltage is less than 140Vac, the output load of the LED driver is required to linearly decrease as the input voltage decreases. According to the above derating curve and corresponding requirements, when choosing a LED driver, actual applying needs are important, as well as the derating margin. 1.3 LED Working CharacteristicsWhen the required input power is a fixed value, such as a fixed error of 5%, the output current can only be adjusted to the specified power for each lamp. Due to different working ambient temperature and different lighting time, the power of each lamp will vary greatly.Although there are considerations for marketing and business factors. However, the volt-ampere characteristic of the LED lamp determines that the LED driver is a constant current source, and its output voltage varies with the series voltage Vo of the LED load. When the efficiency of the driver is basically unchanged, its input power changes with Vo. And meanwhile, the overall efficiency of the LED driver will increase after thermal equilibrium. Under the same output power, the input power will decrease compared to the boot time.Therefore, when formulating requirements, LED driver users should first understand the operating characteristics of LEDs. Avoid suggesting indicators that do not meet the principles of operating characteristics, and indicators that far exceed actual requirements, resulting in excess quality and cost waste. 1.4 Test SessionSample test problems, for example, multi-brand LED driver samples all failed during the test. The reason is that a self-dual voltage regulator is used to directly power the LED driver for testing. After power on, the voltage regulator is gradually adjusted from 0Vac to the rated operating voltage of the LED driver. This kind of test operation can easily make the LED driver start and work with the load when the input voltage is very small, but this situation will cause the input current to be far greater than the rated value. And the internal input terminal related components, such as fuses, rectifier bridges, thermistors, etc. will fail due to excessive current or overheating, damaging the LED driver.The correct test method is to adjust the voltage regulator to the rated operating voltage range of the LED driver, and then connect the driver to power-on test. Of course, technically improving the design can also avoid the failure caused by this kind of test misoperation. That is, a starting voltage limit circuit and an input undervoltage protection circuit are set at the input of the driver. When the input does not reach the start-up voltage set by the driver, the driver does not work. When the input voltage drops to the input undervoltage protection point, the driver enters the protection state. Although the driver has a self-protection function and will not fail, you must carefully understand whether the purchased LED driver product has this protection before testing (considering the actual application environment of the LED driver, most LED drivers currently do not have this set). 1.5 Different Load with Different Test ResultsOn the one hand, when the LED driver is tested with LED lights, the result is normal; on the other hand, when driver tested with an electronic load, the result may be abnormal. Usually this phenomenon has the following reasons:1) The output instantaneous voltage or power of the driver exceeds the working range of the electronic load instrument. (Especially in CV mode, the maximum test power should not exceed 70% of the maximum power of the load. Otherwise, the load may instantaneously have overpower protection when loading, causing the driver to fail to work.)2) The characteristics of the electronic load instrument used are not suitable for measuring constant-current device. And the load voltage gear jumping, result in the drive to fail to work.3) Because there is a large capacitor inside the input of the electronic load meter. The test is equivalent to connecting a large capacitor in parallel with the driver output, which may cause the driver's current sampling work to be unstable. As we all known, the LED driver is designed to meet the working characteristics of LED lamps. The most practical test method is to use the LED lamp as a load, and connects an ammeter and a voltmeter in series to test. 1.6 LED Driver Circuit ProblemThe following conditions often cause damage to the LED driver:Connect AC to the DC output terminal of the driver, causing the driver to fail.Connect AC to the DC/DC output or input of the driver, causing the driver to fail.Connect the output terminal of the constant current to the dimming light, causing the driver to fail.Connect the phase wire to the ground wire causing the driver has no output and the housing is charged. 1.7 Wrong Phase WringTake an international example: the rated working voltage between each phase line and the neutral line is 220V, and the voltage between the phase line and the phase line is 380V. If the driver is connected to two phase wires, after power on, the LED driver input voltage exceeds the rated range, which cause the product to fail.As shown in Figure 3, V1 represents the first phase voltage, V2 represents the second phase voltage, and R1 and R2 respectively represent the drivers normally installed on the line. When the neutral line (N) on the circuit is disconnected, the drivers R1 and R2 on the two branches are connected to the 380V voltage after being connected in series. Because of the difference in input internal resistance, when one of the drivers is charged to start, the internal resistance becomes smaller. Most of the voltage may be applied to another driver, causing the overvoltage damage. Therefore, it is recommended that switches or short-circuiters on the same distribution branch should be disconnected together, not just cut off the neutral line. What’s more, do not put the power distribution fuse on the neutral line to avoid bad effect of the neutral line on the circuit.Figure 3. Neutral Line Open Circuit Diagram 1.8 Grid FluctuationWhen wires of a transformer grid branch is too long and there is large power equipment on the branch, the grid voltage will fluctuate sharply when the large equipment starts and stops. It even causes the grid to be unstable. When the grid voltage exceeds 310V, the drive may be damaged (even if there is an LED lightning protection device, it is useless. Because the lightning protection device is to deal with pulse spikes of tens of uS level, and the fluctuation of the grid may reach tens of mS, or even hundreds of mS) . Therefore, special attention should be paid when there is large electric machinery on the street lighting branch power grid. It is best to monitor the fluctuation range of the power grid or to supply power to the grid transformer separately. 1.9 Frequent Line TripsToo many lights are connected on the same branch, which leads to overload on a certain phase and uneven power distribution among the phases, resulting in frequent line trips. 1.10 Drive CoolingAlthough the LED has high luminous efficiency, only a small part of the energy flowing through the LED is radiated in the form of visible light. And most of the remaining energy is consumed in the LED in the form of heat, so the LED generates more serious heat. When the driver is installed in a non-ventilated environment, the driver housing should be in contact with the lamp housing as much as possible. If possible, apply thermal glue or a thermal pad on the contact surface between the housing and the lamp housing to improve the heat dissipation of the LED driver and ensure the reliability of the driver.Ⅱ LED Driver Maintenance2.1 Multimeter to Detect LED DriverMeasuring the output voltage of the no-load LED driver with a multimeter, if the output voltage is not detected, does it mean that the driver is broken? Look at the following steps:1) The voltage of the non-isolated LED power supply in the no-load state is about 300V tested with a multimeter, and it is about 220V with a PFC.2) Isolating the LED power supply, the voltage in the no-load state, tested with a multimeter, is about 3-5V more than the total voltage of the rated LED series. However, although the output voltage can be tested under no load, it does not mean that it can be normal under load. At this time, it is necessary to connect the corresponding LED light board to see the performance of the LED lighting. If there is no flicker, the output voltage is also equal to the total voltage of LED lights in series connection. This situation can be considered normal, otherwise it fails. If there is no output voltage at no load, the power supply must be broken. 2.2 Identify LED Power SupplyThe LED power supply is widely used in many applications. So how to distinguish the quality of LED power supply is particularly important. A few methods are briefly introduced below. LED Driver ICThe power of IC drive, the quality of IC directly affects the whole power supply. The lighting manufacturer should understand the IC design solution and calculate the cost of the driver, so as to purchase power products at a reasonable price. TransformersThe control chip can be regarded as the brain center of the power supply, while the transformers determine the power and temperature resistance. The transformer is responsible for the transfer of "AC to DC". However, the energy overload will damage the device. The core of the transformer is the magnetic core and the wire package. Electrolytic Capacitors and Ceramic CapacitorsThe quality and life requirements of input electrolytic capacitors are important. However, people tend to ignore the quality requirements of the output capacitor. In fact, the life of the output capacitor also has a great impact on the life of the power supply. The output end has a switching frequency of up to 60,000 times per second, which causes the parasitic resistance of the capacitor to heat up and produce substances similar to scale. Finally, the electrolyte heats up and bursts. Ceramic capacitors: The materials are divided into X7R, X5R and Y5V, and the actual capacitance value of Y5V can only reach 1/10 of the actual value. In addition, the nominal capacitance value only refers to when a capacitor works at 0V. Therefore, this tiny chip with poor options will also lead to a price difference in cost and greatly shorten the life of the power supply. Circuit Design and Welding ProcessJudgment of the pros and cons of the design: Aside from the professional point of view, it can be distinguished by some intuitive methods, such as the neat layout of the components, and soldering points. As for flying leads and manually adding components, it is a serious lack of techniques and efficiency. As we all know, the quality of mechanized production of wave soldering process is definitely better than manual welding. Because the machining process is more neat and uniform. Identification method: whether there is red glue on the back board.The flashing phenomenon of the lamp after a period of use is basically caused by the power supply or the weak welding of the lamp beads. However, it is extremely difficult to detect the virtual welding of products through aging, so AOI must be used to detect the quality of the power supply. Batch Inspection of Aging Racks and High Temperature Aging RoomsNo matter how good the power products are controlled by materials and production processes, they still need to be tested for aging. Because the incoming inspection of electronic components and transformers is difficult to control. Only through the aging of the entire batch of power supplies and the high temperature sampling inspection of the high temperature room. This is a wide-ranging screening to determine whether the materials have safety hazards. Ⅲ LED Driver Circuit ModulationThe LED driver circuit is divided into constant-voltage type and constant-current type according to the power supply to the LED. Constant-current switch type LED driver circuit samples the current flowing through the LED lamp, and gives the output control signal to control the on and off of the switching power tube, which aims to adjust the output current as the set value. The dimming control circuit mainly includes SCR dimming circuit, pulse width modulation (PWM), pulse frequency modulation (PFM), sliding mode control, PWM_PFM, PSM, etc. Let's take pulse width modulation (PWM), pulse frequency modulation (PFM), and sliding mode modulation to introduce in detail below. 3.1 Pulse Width Modulation (PWM)Pulse width modulation, shown in the figure below, refers to the stability of the output voltage by changing the on-time of the switching power tube in each cycle at a specific frequency. That is adjusting the duty cycle to obtain stable output voltage. When the output voltage changes due to the working environment, noise and other factors, the error amplifier samples the voltage change and sends the signal to the control circuit. The control circuit adjusts the duty cycle of the switching power tube signal to maintain the stability of the output voltage.Figure 4. PWM Modulation Based on BUCK StructureFigure 4 (a). Voltage ModeFigure 4 (b). Peak Current ModeFigure 4 (c). Average Current Mode3.1.1 Advantages of PWM(1) The PWM modulation method has high efficiency under heavy load, and has a good dynamic response to load changes.(2) The output ripple voltage is small and the linearity is high.(3) The frequency is stable, the duty cycle adjustment is not restricted, the control is simple, and both the current control mode and the voltage control mode are applicable.3.1.2 Disadvantages of PWM(1) The efficiency of PWM modulation method decreases at light load.(2) The transient response is slow during constant-voltage driving, and a more complicated compensation circuit is required.(3) Accurate current detection circuit is required for constant-current driving. 3.2 Pulse Frequency Modulation (PFM)The pulse frequency modulation is shown in the figure below. Under the condition of a certain on-time of the switching power tube, the output voltage can be controlled by adjusting the off time. When the output voltage changes, the error amplifier samples the feedback signal and sends the output signal compared with the reference signal to the control circuit. The control circuit analyzes the error signal and generates a square wave signal with constant pulse width and varying frequency to control the switch power tube to maintain the stability of the output voltage.Figure 5. Pulse Frequency Modulation Based on BUCK Structure3.2.1 Advantages of PFM(1) The PFM modulation has very high efficiency, better frequency characteristics and higher voltage regulation rate at light load.(2) The PFM modulation has a relatively high transmission signal-to-noise ratio and a good anti-interference ability.(3) The output voltage has a large adjustable range and low power consumption.3.2.2 Disadvantages of PFM(1) The efficiency of the PFM modulation will decrease under heavy load.(2) The frequency spectrum of the output ripple is scattered and irregular.(3) The load adjustment range is very small, resulting in high filtering costs. 3.3 Sliding-Mode ModulationSliding-mode modulation mode, the full name is sliding mode variable structure control,  is a discontinuous control. As shown in Figure 6, the sliding mode makes the system structure change purposefully according to its current state, which force the system to make small amplitude and high frequency up and down movements along the designed trajectory under response conditions. That is, sliding mode movement. Reduce the system's sensitivity to disturbances and load jumps.Figure 6. Sliding Mode Control Based on BUCK Structure3.3.1 Advantages and Disadvantage of Sliding ModeIt has the advantages of fast dynamic response, strong robustness and wide stability range, but it also has a problem that the operating frequency is not fixed. Ⅳ One Question Related to LED Driver4.1 QuestionHow long do LED drivers last?4.2 AnswerWhile the light function of an LED may last for years, drivers can give out much sooner. This is why we recommend name brand LED bulbs for the home, especially those with 25,000 hour rated lives. In general, high power white LEDs use much more current, and need of more complicated drivers. Frequently Asked Questions about LED Drivers Failure Analysis and Maintenance1. What is a LED driver IC?They are configured as either inductorless (charge pump) or switching regulator-based LED drivers that support driving white LEDs in series, parallel or combination. ... Topologies include boost regulator, buck regulator, buck/boost, SEPIC topology LED drivers, and more. 2. What is a LED driver used for?LED drivers are electrical devices that prevent damage to LEDs by regulating the forward voltage (VF) of the LED that changes with temperature, avoiding thermal runaway while delivering a constant current to the LED. LED drivers also aid efforts to meet new energy requirements (e.g., Energy Star). 3. How do I choose an LED driver?Use an LED driver with at least the same value as your LED(s). The driver must have a higher output power than your LEDs require for extra safety. If the output is equivalent to the LED power requirements, it is running at full power. Running at full power may cause the driver to have a shorter life span. 4. Why do LED drivers fail?LED FailureThe LEDs usually fail, because they have been connected to a constant LED driver in parallel. If the LEDs have failed you may want to also replace the LED driver. We usually recommend using a model with an adjustable output, and trimming down the output voltage slightly, to avoid over powering the LEDs. 5. How long do LED drivers last?Namely, the life of the driving circuit expires prior to when the LED stops emitting light or has its brightness dropped. The typical nominal lifetime of these elements is often times less than 25,000 hours, while the lifetime of LED itself could be as long as 50,000-100,000 hours. 6. Why do my LED drivers get hot?If the LED driver is trying to draw DC (not a balanced load circuit) then that can also cause the transformer to overheat.7. What is the difference between a transformer and an LED driver?LED drivers and electronic transformers for retrofit LED lighting are not interchangeable. They differ in output and load compatibility i.e. which LED lights they will work with. The fundamental difference between the two is that LED drivers output DC while electronic halogen transformers output 12VAC.

CatalogI IntroductionII What is Infrared?III Theoretical Principle of Infrared Temperature MeasurementIV The Principle of Infrared ThermometerV Differences in Accuracy of Different Types of Infrared Thermometers  5.1 Three Categories of Infrared Thermometers  5.2 Differences Between Mainstream Infrared Thermometers  5.3 Infrared Temperature GunVI Infrared Thermometer Accuracy And Factors Affecting Accuracy  6.1 Precision of Infrared Thermometer  6.2 Factors Affecting The Accuracy of The Infrared Thermometer MeasurementVII Factors to Consider When Choosing An Infrared ThermometerVIII How To Make Infrared Thermometers More AccurateIX One Question Related to Infrared Thermometers  9.1 Question  9.2 AnswerX FAQI IntroductionIn the past two months, due to the outbreak of Coronavirus Disease 2019 (COVID-19), output of infrared thermometers exceeded the whole year of last year, driving the shipments and demand for chips such as sensors, MCUs, and operational amplifiers. Infrared thermometer is a non-contact diagnostic technology that can scan and image the thermal radiation of objects and display data. It has the advantages of wide measurement range, fast temperature measurement, high accuracy and high sensitivity. With the widespread use of infrared thermometers, some users have doubts about its working principle and accuracy. This article will introduce how the infrared thermometer works, and explain its accuracy and the factors that affect it.Figure1. Infrared ThermometerII What is Infrared?Infrared is an electromagnetic wave with a wavelength between microwave and visible light. The wavelength is between 1mm and 760 nanometers (nm), which is invisible light longer than red light. Anything above absolute zero (-273.15°C) can generate infrared rays. Modern physics calls it heat rays. Medical infrared can be divided into 2 categories: near infrared and far infrared. Containing thermal energy, the sun's heat is mainly transmitted to the earth through infrared rays. Infrared is a part of the many invisible rays of the sun's rays. It was discovered by British scientist Herschel in 1800 and is also called infrared thermal radiation. It has a strong thermal effect. He split the sunlight with a prism, and placed thermometers on the ribbons of various colors in an attempt to measure the heating effect of light of various colors. It was found that the thermometer located outside the red light warmed the fastest.  Therefore, it is concluded that in the solar spectrum, there must be invisible light outside the red light, which is infrared. Can also serve as a medium of transmission. The wavelength of infrared light in the solar spectrum is greater than visible light, with a wavelength of 0.75 to 1000 μm. Infrared can be divided into three parts, namely near infrared, with a wavelength between (0.75-1) to (2.5-3) μm; mid-infrared, with a wavelength between (2.5-3) to (25-40) μm; far infrared , The wavelength is between (25-40) ~ l500μm.Figure2. InfraredIII Theoretical Principle of Infrared Temperature MeasurementIn nature, when the temperature of an object is higher than absolute zero, due to the existence of internal thermal movement, it will continuously radiate electromagnetic waves to the surroundings, including infrared rays with a wavelength range of 0.75µm ~ 100µm. Its biggest feature is that at a given temperature and wavelength, the radiant energy emitted by an object has a maximum value.  This substance is called a black body, and its reflection coefficient is set to 1; the reflection coefficient of other substances is less than 1, and is called gray body. Because the black body's spectral radiant power P (λT) meets Planck's law between the absolute temperature T, it shows that at the absolute temperature T, the radiant power of the black body per unit area at the wavelength λ is P (λT). According to this relationship, the relationship curve can be obtained as shown in the figure below: (1) As the temperature increases, the stronger the radiant energy of the object. This is the basis of the theory of infrared radiation and the design basis of a single-band infrared thermometer. (2) As the temperature rises, the radiation peak shifts to the short-wave direction (to the left) and satisfies the Wien shift theorem. The wavelength at the peak is inversely proportional to the absolute temperature T, and the blue curve is the line connecting the peaks. This formula tells us why the high temperature thermometer works mostly in the short wave and the low temperature thermometer works mostly in the long wave. (3) The rate of change of radiant energy with temperature is larger at the short wave than at the long wave, that is, the thermometer working at the short wave has a relatively high signal-to-noise ratio (high sensitivity) and strong anti-interference. This is particularly important at wavelengths, especially for small targets at low temperatures.Figure3. Planck's Law of Blackbody RadiationIV The Working Principle of Infrared ThermometerThe infrared thermometer consists of the optical system, photodetector, signal amplifier, signal processing and display output. The radiation of the measured object and the feedback source is adjusted according to the modulator and input to the infrared detector. The difference between the two signals is amplified by the inverse amplifier and the temperature of the feedback source is controlled so that the spectral radiance of the feedback source is the same as that of the object. The display indicates the brightness temperature of the object being measured.How does an Infrared Thermometer work?V Differences in Accuracy of Different Types of Infrared Thermometers5.1 Three Categories of Infrared ThermometersAccording to different uses and accuracy, infrared thermometers can be roughly divided into medical-grade infrared thermometers, consumer-grade infrared thermometers, and industrial-grade infrared thermometers. Strictly divided, medical-grade infrared thermometers have the highest accuracy requirements. The accuracy needs to be between 0.1 and 0.2 degrees. High-precision infrared ear thermometers can meet the medical-grade temperature standards. However, to avoid cross-infection, hospitals use ear thermometers. One-time sheath is needed for warm guns; consumer grades are next, and accuracy around 0.5 can meet our daily temperature measurement needs. The accuracy is about 0.3 degrees, which belongs to the consumer-grade infrared thermometer; the industrial grade has the lowest, generally the maximum allowable error is more than ± 1 ° C, and the distance is far.5.2 Differences Between Mainstream Infrared ThermometersIn fact, whether it is a medical or industrial infrared thermometer, they use the same principle of receiving infrared waves from the human body, but the object distance ratio has been adjusted differently, and the surface temperature is measured. The normal forehead temperature is about 2-3 ° C lower than the temperature of the armpit, and the forehead is directly affected by the environment. It is for preliminary investigation and reference and cannot be used as a basis for medical diagnosis. In addition, the temperature of the ear and neck will be more stable than the temperature of the forehead and barely affected by the environment. This is one of the reasons why the ear thermometer is more accurate than the forehead.5.3 Infrared Temperature Gun The medical thermometer has been revised by software or the relevant range has been limited by the software before leaving the factory. The emissivity of a normal human body is 0.98 (the thermometer defaults to 0.95), so the measured result is about 34-35 ° C. All infrared products (infrared cameras) can correct the difference by changing the emissivity to 0.8 to avoid inaccurate body temperature when used by non-professionals; and industrial-grade thermometers provide more realistic feedback on temperature measurement. It shows the actual temperature detected.Figure4. Infrared Temperature GunVI Infrared Thermometer Accuracy And Factors Affecting Accuracy6.1 Precision of Infrared ThermometerThe accuracy of contact measurement is about 0.1 degrees. Compared with contact temperature measurement, the accuracy of non-contact temperature measurement is lower. The infrared thermometer with higher accuracy is about 0.2 degrees, and the worse temperature error is 1 degree. Even above 1 degree. In general, the accuracy of infrared thermometers is ± 2 ° C. Today, temperature measurement products such as handheld infrared thermometers on the market are easily affected by measurement distance and ambient temperature, and the measurement error is often around 1 degree.6.2 Factors Affecting The Accuracy of The Infrared Thermometer Measurement6.2.1 EmissivityAll objects reflect, transmit, and emit energy, and only the emitted energy can indicate the object's temperature. When the infrared thermometer measures the surface temperature, the instrument can receive all three kinds of energy. Therefore, all infrared thermometers must be adjusted to read only the emitted energy. Measurement errors are usually caused by infrared energy reflected from other light sources.  Some infrared thermometers can change the emissivity, and emissivity values for many materials can be found in published emissivity tables. Other instruments have a fixed pre-set emissivity of 0.95. The emissivity value is the surface temperature of most organic materials, paints or oxidized surfaces, which is compensated by applying a tape or flat black paint to the measured surface. When the tape or lacquer reaches the same temperature as the base material, measure the temperature of the surface of the tape or lacquer, which is its true temperature.Figure5. Emissivity6.2.2 Ratio of Distance To Light SpotThe optical system of the infrared thermometer collects energy from a circular measurement spot and focuses it on the detector. The optical resolution is defined as the ratio of the distance from the infrared thermometer to the object to the size of the measured spot (D: S). The larger the ratio, the better the resolution of the infrared thermometer and the smaller the spot size to be measured. 6.2.3 Field of ViewMake sure the target is larger than the spot size of the infrared thermometer. The smaller the target, the closer it should be. When accuracy is particularly important, make sure the target is at least 2 times the spot size.Figure6. Field of ViewVII Factors to Consider When Choosing An Infrared Thermometer(1) Temperature rangeThe temperature measurement range is actually the range of the infrared thermometer, and the range of different thermometers will be different. The temperature measurement range is generally -50 ~ 360 ° C, -30 ~ 380 ° C, -18 ~ 280 ° C, -32 ~ 450 ℃, -32 ~ 650 ℃, -32 ~ 1050 ℃, etc., and the range for measuring body temperature is generally 35 ~ 42.5 ℃. You need to choose the appropriate range according to the temperature range of the measured object. (2) Measurement accuracyMeasurement accuracy is the only indicator to ensure the accuracy of the measurement, and it is also a key indicator to determine the performance of the infrared thermometer. Accuracy is usually expressed as ± X ℃ or ± X%. The smaller the value, the higher the accuracy. (3) Display resolutionThe display resolution is the last digit of the temperature display, usually 0.1 ° C or 0.1 ° F. (4) Optical resolutionThe optical resolution is the ratio of the distance D from the thermometer to the target to the diameter S of the measurement spot, that is, the ratio of the distance to the spot diameter D; S, D: S, the greater the accurate temperature measurement distance. In order to obtain accurate temperature readings, the distance between the thermometer and the test target must be within a suitable range. If the pyrometer must be measured away from the target due to environmental conditions, and a small target is to be measured, a pyrometer with high optical resolution should be selected. (5) EmissivityEmissivity is the ratio of the energy radiated by an object at a specific temperature to the energy radiated by an ideal radiator at the same temperature. Different objects have different emissivities. Some infrared thermometers have a fixed emissivity of 0.95, while others are adjustable. The emissivity of the infrared thermometer can be adjusted according to the material of the measured object to ensure the accuracy of the measurement results. (6) Response timeThe response time is the time it takes for the infrared thermometer to reach 95% of its final reading. It represents the speed at which the infrared thermometer responds to changes in the measured temperature. The response time of the new infrared thermometer can even reach 1ms. If the target moves fast or measures a fast-heated target, a fast-responding infrared thermometer should be selected; otherwise, a sufficient signal response cannot be achieved, which will reduce the measurement accuracy.Figure7. Infrared ThermometerVIII How To Make Infrared Thermometers More Accurate(1) Accurately determine the emissivity of the measured object;(2) Avoid the influence of high-temperature objects in the surrounding environment;(3) For transparent materials, the ambient temperature should be lower than the temperature of the measured object;(4) The thermometer should be vertically aligned with the surface of the measured object. Under no circumstances should the angle exceed 30 ° C.(5) Can be applied to the temperature measurement of bright or polished metal surfaces, and cannot be measured through the glass;(6) Correctly follow-off coefficient, the target diameter is full of field of view;(7) If the infrared thermometer is suddenly in a situation where the ambient temperature difference is 20 ° C or higher, the measurement data will be inaccurate, and then take the measured temperature value after the temperature is balanced. IX One Question Related to Infrared Thermometers9.1 QuestionWhat is infrared radiation?A. It's the transfer of energy by electromagnetic wavesB. The radiation given off by radioactive particlesC. Infrared radiation is a type of gasD. It is the reaction that occurs by freezing water9.2 AnswerA X FAQ1. How do you accurately use an infrared thermometer?Keep the Infrared Thermometer Close to the TargetThe Distance-to-spot ratio is the surface area being able to be detected compared to the distance taken from the target. As a rule of thumb, the closer you are to the target, the smaller the measurable surface area is, thus the more accurate the measurement. 2. How does the infrared temperature sensor work?These sensors work by focusing the infrared energy emitted by an object onto one or more photodetectors. These photodetectors convert that energy into an electrical signal, which is proportional to the infrared energy emitted by the object. 3. How accurate are thermal thermometers?Research has shown that, when used correctly, infrared or no-contact thermometers are just as accurate as oral or rectal thermometers. No-contact thermometers are popular among pediatricians, as kids often squirm around when trying to get a temperature read, but it also holds true in mass temperature screenings. 4. What is normal forehead temperature with an infrared thermometer?Normal forehead skin temperature can vary several degrees depending on your environment (indoors or out), exercise, perspiration, direct heat or air conditioning, etc. It would be normal to read an actual forehead skin surface temperature between 91F and 94F if using a general-purpose infrared thermometer. 5. Are infrared thermometers dangerous?As long as the Non-Contact Infrared Thermometers are used properly, they do not represent a risk of possible eye damage, as these Thermometers do not use lasers to measure body heat, the authorized thermometers measure infrared light; therefore they are not dangerous. 6. How far away should you hold an infrared thermometer?Usually, 6 inches is considered the ideal distance for using an infrared thermometer and correctly monitoring the temperature. 7. What is the benefit of using an infrared thermometer?IR thermometers are handy for use in measuring drafts and insulation breakdown. They can pick up hot spots in electrical systems and bearings and help monitor cooling systems. They are even used to measure food storage temperatures and can do this with no cross-contamination. 8. Are digital or infrared thermometers more accurate?Ranging from 0 to 600 Fahrenheit, the best IR Thermometer has a correct accuracy of about ±3.5 Fahrenheit. A digital thermometer could be used in three different ways. The accuracy of each might differ from one another. 9. What are the benefits of a non-contact infrared thermometer?• The non-contact approach may reduce the risk of spreading disease between people being evaluated.• Easy to use.• Easy to clean and disinfect.• Measures temperature and displays a reading rapidly.• Provides the ability to retake a temperature quickly. 10. How do I know if my digital thermometer is accurate?Add a little clean water until the glass is full and stir. Wait for about three minutes before inserting the sensor on the thermometer into the ice-filled water. Wait for about thirty seconds and check that the thermometer reads 32°F. If it does, then it is accurate, but if not, it requires calibration. 

IntroductionA diode is a fundamental PN junction semiconductor device in the realm of microelectronics. Structurally, it consists of P-type (positive) and N-type (negative) semiconductor materials joined together. Ideally, it functions as a one-way switch, allowing electrical current to flow easily in one direction (forward bias) while severely restricting it in the opposite direction (reverse bias).The 1N4007 diode is the most popular member of the silicon 1N400x series family. It is a general-purpose rectifying diode widely used to convert alternating current (AC) signals into direct current (DC) in power supplies and electrical appliances.This tutorial will discuss its pinout, technical specifications, modern equivalents (including SMD versions), example circuits, and practical applications.Electronic Project Idea utilizing Switch, LED, and 1N4007 DiodeⅠ What is the 1N4007 Diode?The 1N4007 diode is a non-linear semiconductor device that enforces unidirectional current flow. Current flows from the Anode (positive) to the Cathode (negative).The 1N4007 is specifically designed for high-voltage rectification. While its continuous current carrying capacity is 1 Ampere (1A), it can withstand non-repetitive surge currents (peaks) of up to 30A (typically for a duration of 8.3ms, or one half-cycle of 60Hz AC).Modern Context: While the 1N4007 is the "Through-Hole" (Axial) version, the industry has largely moved toward Surface Mount Devices (SMD). The SMD equivalent of the 1N4007 is known as the M7 Diode.Because these diodes block reverse voltage effectively, they are critical in building rectifiers. Using a diode with a lower voltage rating than required can lead to component breakdown and circuit failure.Ⅱ 1N4007 Diode PinoutThe graphic below depicts the logic symbol and physical pinout of a 1N4007 diode:The logic symbol pinout of 1N4007 diodeForward Bias vs. Reverse BiasWhen the voltage at the Anode is more positive than the voltage at the Cathode, the diode is "Forward-Biased." In this state, it conducts electricity. The 1N4007 typically has a forward voltage drop of approximately 0.7V to 1.1V depending on the current load.Conversely, when the Cathode voltage is more positive than the Anode, the diode is "Reverse-Biased." Theoretically, it acts as an open switch. However, in reality, a minuscule "leakage current" (approx 5 µA) does flow. If the reverse voltage exceeds the diode's rating (1000V for the 1N4007), the diode will experience avalanche breakdown and likely fail.The 1N4007 pinout diagram showing the cathode band.2.1 Pin ConfigurationPin NumberPin NameDescription1AnodePositive (+Ve) terminal where current enters.2CathodeNegative (-Ve) terminal where current exits. Marked by a Grey/White band on the body.2.2 Reverse Recovery TimeThe 1N4007 is a standard recovery diode. When switching from forward conducting to reverse blocking, it requires a finite amount of time to clear charge carriers from the junction. This is called "Reverse Recovery Time" ($t_{rr}$).Because the $t_{rr}$ for a 1N4007 is relatively slow (typically around 2µs to 30µs), it is not suitable for high-frequency applications (like modern switching power supplies operating at >50kHz). It is best suited for low-frequency inputs (50Hz/60Hz mains rectification).Ⅲ 1N4007 Features and SpecificationsBelow are the corrected standard specifications for the 1N4007:Max Repetitive Reverse Voltage ($V_{RRM}$): 1000VAverage Rectified Forward Current ($I_{O}$): 1.0 ANon-Repetitive Peak Forward Surge Current ($I_{FSM}$): 30 A (for 8.3ms single half sine-wave)Operating Junction Temperature ($T_J$): -55°C to +150°C (some manufacturers rate up to +175°C)Forward Voltage Drop ($V_F$): ~1.0V to 1.1V at 1AReverse Current ($I_R$): ~5 µA at full rated voltage (25°C)Package Type: DO-41 (Plastic Axial)Technical Parameters TablePackage DescriptionDO-41 (Plastic Axial) / M7 (SMD Equivalent)StatusActive (Widely Available)Component TypeGeneral Purpose RectifierMaterialSiliconPeak Reverse Voltage1000 VPower Dissipation3.0 W (Ideal condition) / Typically 1.0 W in free airⅣ Applications of 1N4007 DiodePower Supply Rectification: Converting AC Mains to DC (Half-wave and Full-wave bridge rectifiers).Reverse Polarity Protection: Preventing damage to circuits if a battery is inserted backward.Flyback Diode: Connected across inductive loads (like motors or relay coils) to suppress voltage spikes when turned off.Logic Gates: Used in simple DTL (Diode-Transistor Logic) implementations.Ⅴ 1N4007 Diode Replacement and EquivalentDirect Equivalents: 1N4007G (Green/Halogen Free), 1N5408 (Higher current capacity: 3A), HER208 (High Efficiency), 1N5822 (Schottky).⚠️ Critical Warning: The 1N4148 is often suggested as a diode equivalent, but it is a Signal Diode with a max current of only 300mA. Do not use a 1N4148 to replace a 1N4007 in power applications, or it will burn out immediately.Voltage Ratings within the Series:The 1N400x series are physically identical but rated for different maximum reverse voltages. You can always use a "higher" number to replace a "lower" number, but not vice-versa:1N4004: Max 400V1N4005: Max 600V1N4006: Max 800V1N4007: Max 1000V (Can replace all the above).Ⅵ 1N4007 Diode Example Circuits6.1 Forward and Reverse Biased ModeThe simulation below demonstrates the fundamental switching behavior. In the first circuit (Forward Biased), current flows and the LED lights up. In the second (Reverse Biased), current is blocked.6.2 1N4007 as a Voltage Dropper (Crude Regulator)Since every silicon diode drops approximately 0.6V to 0.7V when conducting, you can arrange them in series to reduce voltage.In the example above, a 9V source is reduced to 3V by using a chain of diodes ($10 \times 0.6V \approx 6V$ drop). Note: This is inefficient and provides poor regulation. For stable voltage, use a dedicated regulator like an LM7805 or LM317.Ⅶ. How Does the 1N4007 Work in a Rectifier?The most common application is the Full Bridge Rectifier. Four 1N4007 diodes are arranged to ensure that regardless of the polarity of the AC input, the output polarity remains constant (DC).A classic bridge rectifier circuit using four 1N4007 diodes to convert AC to DC.Ⅷ How to Test a 1N4007 Diode?Diodes typically fail in one of two ways: Open Circuit (blocks current in both directions) or Short Circuit (allows current in both directions).Using a Digital Multimeter (Diode Mode)Identify Terminals: Locate the grey/white ring; this is the Cathode (-). The other end is the Anode (+).Set Multimeter: Turn the dial to the Diode Test mode (usually indicated by a diode symbol).Forward Bias Test: Place the Red probe on the Anode and Black probe on the Cathode.Good Reading: 0.5V to 0.7V.Bad Reading: "OL" (Open) or 0.00V (Short).Reverse Bias Test: Swap the probes (Red on Cathode, Black on Anode).Good Reading: "OL" or "1" (No continuity).Bad Reading: Any voltage reading indicates leakage or a short.Ⅸ FAQ1. Can I replace a 1N4001 with a 1N4007?Yes. The 1N4007 has a higher reverse voltage rating (1000V) than the 1N4001 (50V), making it a superior and safe upgrade.2. Is the 1N4007 a Schottky Diode?No. The 1N4007 is a standard silicon PN junction rectifier. Schottky diodes (like the 1N5819) have lower forward voltage drops and faster switching speeds but usually lower reverse voltage ratings.3. Can I use a 1N4007 for high-frequency switching?No. Due to its slow reverse recovery time, 1N4007 is suitable for 50Hz/60Hz mains rectification. For high-frequency switching (e.g., SMPS), use "Fast Recovery" (FR series) or "Ultra-Fast" (UF series) diodes.4. What does "1N" stand for?"1N" is JEDEC notation. "1" indicates the number of PN junctions (one junction), and "N" stands for Semiconductor.5. What is the SMD equivalent of 1N4007?The surface-mount equivalent is the M7 diode, usually found in an SMA or DO-214AC package. table { width: 100%; border-collapse: collapse; margin: 20px 0; background-color: #fff; box-shadow: 0 2px 4px rgba(0,0,0,0.1); } th, td { padding: 12px; text-align: left; border-bottom: 1px solid #ddd; } th { background-color: #f2f2f2; font-weight: bold; } tr:hover { background-color: #f5f5f5; } .highlight-box { background-color: #e8f4f8; border-left: 5px solid #3498db; padding: 15px; margin: 20px 0; } .warning-box { background-color: #fff3cd; border-left: 5px solid #ffc107; padding: 15px; margin: 20px 0; } iframe { display: block; margin: 20px auto; max-width: 100%; } .caption { text-align: center; font-style: italic; color: #666; font-size: 0.9em; }

IntroductionThe relay is an electrical device regarded as a switch in the circuit. That is, the current in the control circuit depends on the "open" and "close" of relay contacts. Therefore, the reliability and service life of the relay depend on the quality and performance of the contacts greatly. The performance of the contact is affected by factors such as contact material, contact voltage, load type, operating frequency, atmospheric environment, contact configuration and bounce.  If any of these factors cannot meet the predetermined value, contact problems such as electrochemical corrosion of the metal between the contacts, contact welding, contact wear, and contact resistance may occur. The volume of the load determines the size of the voltage and current that the relay can control (The rated load of the contact refers to the voltage and current that the electromagnetic relay allows to break.). If you not pay attention to it when use, it is easy to damage the relay contacts.Relay ContactCatalogIntroductionⅠ Relay Contact Form ConfigurationⅡ Relay Contact SymbolⅢ Relay Contact Fault Analysis3.1 Terminology3.2 Contact Bonding and Fusion Welding3.3 Contact Erosion3.4 Contact Metal Migration3.5 Contact Loose and Crack3.6 Contact DustⅣ Contact Protection MethodsⅤ Frequently Asked Questions about Relay ContactⅠ Relay Contact Form Configurationa. Normally Opened ContactIt would mean the contacts are normally open when the coil of the relay is not energized or there is no magnetic field nearby in a reed switch. b. Normally Closed ContactIt would mean the contacts are normally closed when the coil of the relay is not energized or there is no magnetic field nearby in a reed switch. c. Common ContactIt would have 3 leads and would have one normally open and one normally closed circuit. This is also called a “changeover” because the common contact changes from the normally closed position to the normally open position when the coil is energized in a relay or a magnetic field is nearby in a reed switch. Ⅱ Relay Contact Symbol Ⅲ Relay Contact Fault Analysis3.1 TerminologyThere is something in which the relay contact seems to be closed, but the circuit works abnormally sometimes. This is due to the existence of the contact resistance of the relay contacts. When the current passes through the closed contact, the contact resistance will consume a certain amount of power, which will increase the temperature of the contact. If the current is large, the contact material will soften and deform, resulting in greater contact resistance, and even having welding failure in severe cases, making the closed contact unable to be disconnected. Another form of contact resistance is "membrane resistance". Because the contacts of the relay are exposed to the air for a long time, there will always be compounds produced by dust, water vapor, and chemical gas, which will adhere to the contacts to form a thin film. Because of it, the conductivity of the contacts will become worse, and even become non-conductive in severe cases. 3.2 Contact Bonding and Fusion WeldingContact bonding usually occurs when the contacts are in a static connection. Contact resistance making the temperature of the conductive spots and nearby materials increase, which leads to a great increase in the diffusion rate and a large expansion of the contact area. The molecular force formed by the mutual extrusion and penetration of metal molecules at the contact point is the internal factor leading to the contact bonding, in addition, the sliding friction between the contacts is a necessary condition for accelerating the molecular extrusion penetration and accumulating bonding force. The size of the bonding force depends on the rigidity of the contact material and the physical conditions that cause molecular extrusion and penetration. Whether the contacts are bonded depends on the bonding force is greater than the return force of the reed. Fusion welding refers to the phenomenon that the contact areas of two electrodes are united together by metal welding. According to the reasons for formation, welding can be divided into static welding and dynamic welding. The Joule heat generated by the contact resistor melts the contacts part, and the phenomenon that they are combined and cannot be disconnected is called static welding. In the process of the contacts controlling the external circuit, the contact pressure of the contacts is near zero or above, and meanwhile, the liquid metal bridge between the contacts made. The welding phenomenon that occurs owing to the arc heat flow melting the contacts is called dynamic welding. 3.3 Contact ErosionA load of contact switching is mostly inductive. When the inductive load is disconnected, its accumulated magnetic energy will generate a high back electromotive force at both ends of the contact, which will break up the air gap between the contacts to form sparks and cause electrical corrosion. Cause the contact surface to dent or stick and cannot be separated, all of them belong to poor contact, which will result in a short circuit. The main factors that affect arc erosion include the characteristics of the arc and its effect on the heat flow and force of the electrode and the response of the contact material to the heat and force of the arc. In general, there are two main forms of arc erosion: 1) Vaporization and evaporation: Under the action of arc energy, the surface material of the contact changes from solid to liquid, and then into a gaseous state to leave the contact. Except that, in certain conditions, the contact material also has a sublimation process from a solid-state to a gas state. 2) Liquid splashing: Under the action of arc energy, a certain area of the surface of the contact melts. The liquid metal splashes out in the form of tiny droplets under the action of various forces, resulting in a larger material loss. These forces include spot pressure, electrostatic field force, electromagnetic force, force and reaction force of material movement, contact surface tension, etc. The form of arc erosion varies with the contact material and load current conditions. When the load current is small, the erosion of the contact material is dominated by vaporization and evaporation. When the current is increased, not only the vaporization and evaporation of the contact material but also the splashing phenomenon of liquid metal will occur. When the current is further increased, the metal liquid splashing becomes the main form of contact erosion. Preventing electrical corrosion between the contacts can be obtained by setting up a resistance spark extinguishing circuit and a resistance-capacitance spark extinguishing circuit. Therefore, when choosing a relay, you should consider the voltage applied to the contact and the load capacity of the contact. For example a relay with a contact load of 28V(DC)×10A means that the relay’s contact can only work at a DC voltage of 28V, and the contact current is 10A. If these two ratings are exceeded, the service life of the relay will be affected, and even the contacts will be burnt and damaged. In addition, the number of circuits that the relay needs to control should be determined according to actual requirements. In the same model series of relays, there are generally a variety of contact forms for selection, and each group of contacts should be fully utilized when using. 3.4 Contact Metal MigrationDuring the working process, there is usually a mutual transfer of materials between two contacts. If this mutual transfer cannot be offset, a net transfer of materials occurs. The significant contact metal migration is a big net transfer. The asymmetry of various factors in the contact operation is the main reason for the metal migration of the contact. These factors include arc, contact material characteristics and various external forces. Details are as following: 1) The arc has various forms of energy input to the contacts. For the contact at the cathode, the kinetic energy of the ion current colliding with the cathode after being accelerated by decompression, the potential energy released by the ion current on the cathode surface and the electrons, the arc column radiation or the energy conducted to the cathode surface, and the cathode Joule heat generated by the current in the body. All of these energies will increase the temperature of the contact material, resulting in contact material melting and evaporation. 2) The contact has various forces in the working process, including electronic force, electrostatic force, electromagnetic force, the reaction force of material movement, plasma flow force, these forces may cause the metal in the molten pool on the surface of the contact Liquid splashing occurs. 3) The material properties that affect the migration of the contact metal include electrical conductivity, specific heat capacity, latent heat of melting and vaporization, melting point and boiling point, metallurgical dynamics, and so on. In addition, the size, shape, and connection form of the contacts will also affect the metal migration. 3.5 Contact Loose and CrackContacts are electrical contact parts for relays to switch loads. Some products have contacts that are press-fitted by riveting. The main drawbacks of this installing method are loose contacts, cracks in the contacts, or excessive size and so on. They will affect the contact reliability of the relay. The loosening of contacts is caused by the improper size of the mating part of the reed and the contact or the improper adjustment force by the operator. Contact cracking is caused by too high material hardness or too much pressure. Different crafts should be used for contacts of different materials, and some contact materials with higher hardness should be annealed before contact manufacturing, riveting, or welding. 3.6 Contact DustSometime after use, dust and dirt will deposit on the contacts of the relay, which will cause a black oxide film on the surface, resulting in poor contact. Therefore, the contacts need to be cleaned regularly. For example, carbon tetrachloride liquid can be used to ensure good contact performance.  Ⅳ Contact Protection MethodsFigure 1. Contact Oscillogram (contact action time, release time, rebound time and stabilization time)We know that the relay contact protection needs to be more careful than MOSFET. Generally, the load of the relay is much larger than MOSFET. Common DC motors, DC clutches and DC solenoid valves with large DC loads, these inductive load switches are often closed, because surges caused by hundreds of or even thousands of back electromotive force will shorten the life of the contacts or even completely damage them. On the contrary, if the current is small, such as around 1A, the back electromotive force will cause arc discharge, which will cause metal oxides to contaminate the contacts, leading to failure of the contacts and increasing contact resistance. Protect contacts mainly to extend the use time of the relay, because the contacts will always accumulate carbon and age, and the surface is not as clean as it was originally. What’s more, when the relay life is approaching the end, its contact resistance will increase rapidly. Generally, under normal temperature and pressure, the breakdown voltage of the key dielectric in the air is 200~300V. Therefore, our goal is generally to control the voltage below 200V or less.Figure 2. Breakdown VoltageThere generally have the following methods to do it:MethodCircuitCharacteristicComponent SelectionResistor and CapacitorIf the load is related to time, the initial leakage current may cause the load to malfunction.R: The contact voltage is 1VC: The contact current is 1A, and the value of RC varies with the relay and load.The function of the capacitor C is to suppress the excessive voltage when the inductor is discharged.The value of resistance R is determined by the test needs.The breakdown voltage of the capacitor C is 200~300V.If the load is a relay or solenoid valve, the release time will be extended. When the contact power supply voltage range is 24V~ 48V, the voltage across the load is 100 ~ 200V.DiodeThe diode (regarded as a freewheeling diode) acts as a channel for the coil to release energy and a way to dissipate heat. Compared with the RC circuit, it significantly changes the release time of the relay (2~5 times).The reverse breakdown voltage is at least 10 times the power supply voltage, and the forward current is equivalent to the load.Zener DiodeThis circuit effectively prevents the diode from affecting the release time of the relay.The breakdown voltage of the Zener diode must be consistent with the power supply voltage of the relay.VaristorBased on the characteristics of the varistor to stabilize the voltage, this circuit can prevent the contact voltage from being too high, and also slightly delay the relay release time. When the load contact power supply voltage is 24V or 48V, and the voltage across the load is 100 to 200V, the varistor is very effective. * Standard diodes can significantly extend the rebound time. Connecting conventional diodes in series with Zener diodes will affect it lightly. If it is an inductive load, when the contacts are separated, a longer rebound time prolongs the arc generation time and shortens the life of the contacts. For example, a relay with a diode connected to the coil needs 9.8ms to release the contact. Combining the Zener diode with the small signal diode can shorten the time to 1.9ms. In addition, the return time of the relay without a diode connected to the coil is 1.5ms. Although the inductive load is not easy to handle than the resistive load, the use of effective protection will make the performance better. There are two methods that can’t be used.Figure 3. Capacitor and Relay CircuitIn the actual circuit, the protection device (diode, resistor, capacitor, varistor, etc.) and the load should have a certain distance. If the two are too far apart, the effect of the protective device may be weakened. Generally, the distance between the two should be within 50cm. DC loads at higher frequencies will cause abnormal switch corrosion (electric spark generation). When the DC solenoid valve or clutch is controlled at a higher frequency, the contacts may have corrosion. The reason for this is that when an electric spark (arc discharge) is generated, the reaction between nitrogen and oxygen causes contact corrosion. Ⅴ Frequently Asked Questions about Relay Contact1. How do relay contacts work?A relay is an electrically operated switch. They commonly use an electromagnet (coil) to operate their internal mechanical switching mechanism (contacts). When a relay contact is open, this will switch power ON for a circuit when the coil is activated. 2. What is a relay contact output?A relay contact output works basically like an on/off switch. To simplify, if the output is "off" the circuit will be broken (open). If the output is "on" the contact will be made, completing the circuit. Therefore, the controller does not supply any current or voltage itself. 3. Why do relay contacts weld?Consequently, when the contacts are ON again, short-circuited current from the capacitance may cause contact weld. This circuit effectively suppresses arcs when the contacts are OFF. When the contacts are ON again, however, charge current flows to the capacitor, which may result in contact weld. 4. How do I protect my relay contacts?Various ways to protect relay contacts from the effects of switching an inductive load – from left to right: a diode, a spark quench capacitor, Zener diodes or a transil, a varistor. 5. What is a contact form relay?Contact Form: The arrangement of the contacts in the relay. This determines how many circuits the relay can operate. Form 1A (or “1 Form A): One circuit is opened and closed with the contacts in a Normally Open position. 6. What is a relay contact?Relays control one electrical circuit by opening and closing contacts in another circuit. ... When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized. In either case, applying electrical current to the contacts will change their state. 7. How many contacts does a relay have?Two. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke that provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts. 8. What is the difference between relay and contactor?A contactor joins 2 poles together, without a common circuit between them, while a relay has a common contact that connects to a neutral position. Additionally, contactors are commonly rated for up to 1000V, while relays are usually rated to the only 250V. 9. What is the purpose of contactor or relay?A contactor is a large relay, usually used to switch current to an electric motor or another high-power load. Large electric motors can be protected from overcurrent damage through the use of overload heaters and overload contacts. 10. What are the three major parts of a contactor or relay?There are three major parts of a contactor or relay: the coil, mechanical linkage and contacts. The coil is used to create a magnetic field and is rated based on voltage (24 V, 120 V, 208/204 V, 480 V). The mechanical linkage connects the armature to the contacts when the coil is energized, completing the circuit. Recommended ReadingBasic Knowledge of Relay Electronics Tutorial with VideoThe Role of the Relay and Its Working PrincipleHow Relays Work? Relay Functions and Applications

CatalogI IntroductionII Definition, Symbol and Labeling of Variable Resistor  2.1 Definition   2.1.1 What is Variable Resistance?   2.1.2 What is Variable Resistor?  2.2 Symbol  2.3 Labeling Method of Variable ResistorIII How The Variable Resistor WorksIV Features of Variable Resistor ShapeV Structure and Function of Variable Resistor  5.1 Basic Structure  5.2 Schematic Diagram of Two Variable Resistors  5.3 The Role of The Variable ResistorVI Types of Variable Resistors  6.1 Resistance box  6.2 Sliding Rheostat  6.3 Potentiometer  6.4 Specific Classification of Variable Resistors   6.4.1 Film Variable Resistor   6.4.2 Wire Wound Variable ResistorVII Typical Application Circuits of Variable Resistor  7.1 Variable Resistor Circuit in Transistor Bias Circuit  7.2 Stereo Balance Control Variable Resistor CircuitVIII Causes and Solutions of Variable Resistor Malfunctions  8.1 Causes of Variable Resistor Malfunctions8.2 Characteristics of Variable Resistor Malfunctions  8.3 Methods For Repairing Variable Resistor  8.4 Testing a Variable Resistor with a Multimeter   8.4.1 Method   8.4.2 PrecautionsIX Active Variable Resistors with Wide Range of Load ImpedanceX One Question Related to Variable Resistors  10.1 Question  10.2 AnswerXI FAQ I IntroductionA resistor is a current-limiting element. After the resistor is connected to the circuit, the resistance of the resistor is fixed. It generally has two pins, which can limit the current flowing through the branch connected to it. Those whose resistance cannot be changed are called fixed resistors, and those with variable resistance are called potentiometers or variable resistors.Setting Up A Variable Resistor, Rheostat, or Fixed ResistorII Definition, Symbol and Labeling of Variable Resistor2.1 Definition2.1.1 What is Variable Resistance?Variable resistance is a kind of resistance, which can play the role of resistance in electronic circuits. The difference from ordinary resistance is its resistance can be continuously changed within a certain range. In some cases where the resistance value is required to change but does not change frequently, a variable resistor can be used. 2.1.2 What is Variable Resistor？A variable resistor is an electronic component with adjustable resistance. It consists of a resistor and a rotating or sliding system. It is usually used in the circuit that needs to adjust the resistance frequently and plays the role of adjusting the voltage, adjusting the current, or controlling the signal. Its main parameters are basically the same as those of the fixed resistor. 2.2 SymbolThe symbol of the variable resistor is R and the unit is Ω. 2.3 Labeling Method of Variable Resistor(1) The variable resistor uses the direct standard method to indicate the nominal resistance value, that is, the nominal resistance value is directly marked on the variable resistor. In the case of high current applications, the variable resistor is also marked with the rated power parameter. In addition, the resistance value of small variable resistors is expressed in three digits, which is the same as that of resistors.(2) For variable resistors used in small-signal circuits, we generally only care about their nominal resistance and have no power requirements. III How The Variable Resistor WorksWhen a voltage is applied between two fixed electric shocks of the resistor body, the position of the contact on the resistor body is changed by rotating or sliding the system, and a position is formed between the movable contact and the fixed contact. Certainly related voltage. In other words, the resistor body of the variable resistor has two fixed ends. By manually adjusting the rotating shaft or sliding handle to change the position of the moving contact on the resistor body, the relationship between the moving contact and any fixed end is changed. The resistance value changes the magnitude of voltage and current. IV Features of Variable Resistor Shape(1) The volume of the variable resistor is larger than that of the general resistor, and at the same time, the variable resistor in the circuit is less, and it can be easily found in the circuit board.(2) There are three pins in the variable resistor, and they are different from each other. One is a moving pin and the other two are fixed. Generally, the two fixed pins can be used interchangeably, but the fixed and moving pins cannot be used interchangeably.(3) There is an adjustment port on the variable resistor. Use a flat-blade screwdriver to protrude into this adjustment port. Turn the screwdriver to change the position of the moving plate and adjust the resistance value.(4) The nominal resistance value can be seen on the variable resistor. This nominal resistance value refers to the resistance value between two fixed chip pins and is also a fixed chip pin and a moving chip pin. The maximum resistance value between.(5) The vertical variable resistor is mainly used in small-signal circuits. Its three pins are vertically downward and mounted vertically on the circuit board. The resistance adjustment port is in the horizontal direction.(6) Horizontal variable resistors are also used in small-signal circuits. Its three pins are at 90 ° to the resistance plane and are mounted vertically on the circuit board with the resistance adjustment port facing upward.(7) The variable resistance of the small plastic case is smaller and has a circular structure. Its three pins are down and the resistance adjustment port is up.(8) Variable resistors (wire-wound structure) for large power applications. The volume is large, and the moving blade can slide left and right to adjust the resistance. V Structure and Function of Variable Resistor5.1 Basic StructureThe variable resistor is chiefly composed of a moving piece, a carbon film body, and three pins. The three pins are two fixed pins (also called fixed pieces) and one moving piece pin. The moving piece of the variable resistor can be rotated left and right. When using a flat-blade screwdriver to reach into the adjustment port and rotate, the contacts on the moving piece can slide on the resistance piece. According to diverse uses, the resistance material of the variable resistor includes metal wire, metal sheet, carbon film, or conductive liquid. For currents of general magnitude, metal-type variable resistors are frequently used. When the current is slight, it is better to use a carbon film type. When the current is large, the electrolytic type is most suitable. 5.2 Schematic Diagram of Two Variable Resistors Figure3. Schematic Diagram of Two Variable Resistors5.3 The Role of The Variable Resistor(1) A variable resistor is an adjustable electronic component, which is composed of a resistor body and a sliding system. The variable resistor resistance is a resistor that can be adjusted for the current or change of the circuit In the case of circuit resistance, the light can be dimmed, and the motor can be controlled to start its speed. (2) The variable resistor mainly controls the current in the series circuit by changing its own resistance, thereby protecting some electrical components with requirements for the current. The variable resistor is generally used in circuits that do not require frequent adjustment, mainly To fix the same value for the resistor. VI Types of Variable Resistors6.1 Resistance BoxVariable resistors are divided into three types: resistance box, sliding rheostat, and potentiometer. The resistance box is a variable resistance device that uses a conversion device to change its resistance value. This conversion device usually adopts a decimal disc type (knob type) structure, and can also adopt a plug type and an end button type structure as required. The circuit of the resistance box can be divided into series lines and series-parallel lines. Compared with the sliding rheostat, the resistance box can continuously change the resistance in the connected circuit, while the sliding rheostat cannot display the resistance value of the connected circuit.Figure4. Resistance Box6.2 Sliding RheostatA sliding varistor is one of the commonly used devices in electricity. Its working principle is to change the resistance by changing the length of the resistance line in the circuit, thereby gradually changing the current in the circuit. The resistance wire of a sliding rheostat is generally a nickel-chromium alloy with a high melting point and a large resistance, and a metal rod is generally metal with low resistance. As a result, when the cross-sectional area of the resistor is constant, the longer the resistance wire, the greater the resistance; the shorter the resistance wire, the smaller the resistance.Figure5. Sliding Rheostat6.3 PotentiometerA potentiometer is a resistance element with three lead-out terminals whose resistance can be adjusted according to certain change law. A potentiometer usually consists of a resistor and a movable brush. When the brush moves along the resistor body, a resistance value or voltage having a certain relationship with the amount of displacement is obtained at the output end. The potentiometer can be used as a three-terminal element or a two-terminal element. The latter can be regarded as a variable resistor. Because its role in the circuit is to obtain an output voltage that has a certain relationship with the input voltage (external voltage), it is called a potentiometer.Figure6. Potentiometer6.4 Specific Classification of Variable ResistorsThe variable resistor can be divided into the film-type variable resistor and wire-wound variable resistor according to the material. 6.4.1 Film Variable ResistorMembrane variable resistors are usually composed of a resistor body (synthetic carbon film), a movable contact (a movable metal reed or a carbon contact), an adjustment part, and three pins (or solder pads). Two of the fixed pins are connected to both ends of the resistor body, and the other pin (center tap) is connected to the movable contact piece. You can change the resistance between the center tap and the two fixed pins by turning the adjustment part with a small flat-blade screwdriver and changing the contact position of the movable contact with the resistor. Membrane variable resistors are available in hermetic, semi-hermetic, and non-hermetic configurations. (1) Fully sealed film variable resistors are also called solid variable resistors. The resistor is made of carbon black, quartz powder, an organic binder and other materials, and then pressed into plastic or epoxy resin. The matrix of the material is polymerized by heating. The movable contacts use carbon contacts and the adjustment parts are made of plastic. The resistor body and the movable contact are sealed by a metal casing (there is an adjustment hole above the metal casing). Its advantage is that it has good dustproof performance and rarely has bad contact failure. (2) The manufacturing process of the resistor body of the semi-sealed film variable resistor and the resistor body of the fully sealed variable resistor is basically the same. The movable contact piece adopts a metal reed, and the outer plastic cover is sealed. When the plastic cover is rotated, the movable contact piece also rotates with it. This variable resistor is easy to adjust, but its dust resistance is not as good as a fully sealed film-type variable resistor. (3) Unsealed film variable resistors are also called chip tunable resistors. The resistor body is made of carbon black, graphite, quartz powder, an organic binder, etc. to form a suspension, which is coated on a glass fiberboard or glue. Made from wooden boards. The movable contact piece uses a metal reed, and the reed has an adjustment hole, and no separate adjustment component is provided. Its disadvantages are poor dust-proof performance, the contacts are susceptible to oxidation, and prone to failure due to poor contact with the synthetic carbon film. 6.4.2 Wire Wound Variable Resistor(1) High-power wire-wound varistor is also called sliding wire varistor, which is divided into axial ceramic tube-type wire-wound variable resistor and porcelain disc-type wire-wound variable resistor. It adopts an unsealed structure.(2) Low-power wire-wound variable resistors include round vertical wire-wound variable resistors, round horizontal wire-wound variable resistors, and square wire-wound variable resistors, all of which are fully sealed. Package structure.In addition, the variable resistor can be divided into a vertical variable resistor and a horizontal variable resistor according to the structure.Figure7. Wire Wound Variable ResistorVII Typical Application Circuits of Variable Resistor7.1 Variable Resistor Circuit in Transistor Bias CircuitThe figure below shows a variable-resistor voltage-dividing bias circuit. In the circuit, the transistor VT1 constitutes a high-frequency amplifier, and RP1, R1, and R2 constitute a voltage-dividing bias circuit. The output voltage of the voltage dividing circuit is determined by the resistance of three resistors, RP1, Rl, and R2. R1 and R2 are fixed resistors. The variable resistor RP1 is adjusted, and then the VT1 static operating current is adjusted. The amount of current determines whether VT1 can work in the best state. Figure8. Variable Resistance Voltage Divider Bias Circuit7.2 Stereo Balance Control Variable Resistor CircuitThe following figure shows the left and right channel gain balance adjustment circuits in the audio amplifier. RP1 in the circuit is a variable resistor in series with R1. Figure9. Left and Right Channel Gain Balance Adjustment Circuit in Audio AmplifierIn the audio circuit, for a two-channel amplifier, we need to strictly require that the left and right channel amplifiers have an equal gain (balanced), but the discreteness of the circuit components makes this impossible. In order to ensure that the gains of the left and right channel amplifiers are equal, left and right channel gain balance adjustment circuit needs to be provided, which is referred to as a stereo balance circuit. In the right channel circuit, the resistance of R2 is determined, so that the gain of the right channel amplifier is fixed. Taking the gain of the right channel amplifier as a reference, changing the resistance of RP1 so that the gain of the left channel amplifier is equal to the gain of the right channel amplifier can achieve the same gain of the left and right channel amplifiers. VIII Causes and Solutions of Variable Resistor Malfunctions8.1 Causes of Variable Resistor Malfunctions(1) The use time is long, causing oxidation.(2) The failure of the circuit caused the variable resistor to overcurrent and burned the carbon film. At this time, the burned trace of the variable resistor can also be seen from the appearance. 8.2 Characteristics of Variable Resistor Malfunctions (1) Damage to the carbon film of the variable resistorThe carbon film of the variable resistor is worn or burned. At this time, the contact between the moving piece and the carbon film is poor or cannot be contacted.(2) Poor contact between the moving piece of the variable resistor and the carbon film causes the contact resistance between the moving piece and the carbon film to increase.(3) The variable resistor pin is broken. 8.3 Methods For Repairing Variable Resistor (1) When the track of the contact of the moving blade on the carbon film is worn, the contact on the moving blade can be bent inward to change the original track of the contact of the moving blade.(2) The contacts of the moving blade are dirty. You can clean the contacts with pure alcohol.(3) There is a disconnection between one stator and the carbon film. At this time, if it is used as a variable resistor (not used as a potentiometer), this stator that is not disconnected can be used instead. Resistance value.(4) A pin is broken due to twisting. A lead can be welded with a hardwire as a pin.Figure10. Test a Variable Resistor8.4 Testing a Variable Resistor with a Multimeter8.4.1 MethodThe detection method of the variable resistor is basically the same as that of the resistor. The resistance between the primers is measured with an ohmic block. The measurement can be performed directly on the circuit board, or the variable resistor can be disconnected from the circuit. (1) Measure the nominal resistance of the variable resistor. The multimeter is placed in the proper range of the ohmic block. The two-meter bars are connected to the two fixed pin pins of the variable resistor. At this time, the measured resistance value should be equal to the nominal resistance value of the variable electrical accessory, otherwise, the variable resistance is explained. The device is damaged. (2) Measure the resistance between the moving resistor and the stator of the variable resistor. The multimeter is placed in the proper range of the ohmic block. One meter rod is connected to the fixed piece, and the other one is connected to the moving piece. In this measurement state, when the variable resistor moving piece is rotated, the needle is deflected and the resistance value increases from zero To the nominal value, or decrease from the nominal value to zero. 8.4.2 PrecautionsDue to the particularity of the variable resistor, the following issues should be noted during the detection process:(1) If the resistance between the moving piece and a fixed piece is 0Ω, at this time, you should see whether the moving piece has turned to the end of the fixed piece. To exclude the effects of external circuits). (2) If the resistance value between the moving piece and any certain piece is greater than the nominal resistance value, it means that the variable resistor has an open circuit fault. (3) In the measurement, if the measured resistance between a moving piece and a certain piece is less than the nominal resistance value, it does not mean that it is damaged, but you should look at the position of the moving piece, which is different from ordinary resistors. (4) When taking off the measurement, you can use the appropriate range of the multimeter's ohmic stop.-One rod is connected to the pin of the pad, and the other rod is connected to afoot. Then use a flat screwdriver to slowly rotate the pad in a clockwise or counterclockwise direction. At this time, the hands should continuously change from 0Ω to the nominal resistance. The same method is used to measure the change of wake value between another fixed film and a moving film. The measurement method and test result should be the same. In this way, the variable resistor is good, otherwise, the variable resistor is damaged.Figure11. Digital MultimeterIX Active Variable Resistors with Wide Range of Load ImpedancePower resistors, variable resistors, and other electronic loads are often used to test power supplies and voltage regulators, as shown in the following figure: Figure12. Active variable resistors with several orders of magnitude constant resistanceAlthough the function is the same as a mechanical potentiometer, it is based on an active device, which can provide a wide range of load resistance, high resistance adjustment resolution, and less heat than a mechanical potentiometer. Analyzing the circuit shown in the figure above, the voltage expressions of the non-inverting and inverting ends of the operational amplifier are: Figure13. FormulaThese two voltages are equal, so Figure14. FormulaThe whole circuit can be regarded as the resistance of the non-inverting terminal IN + and the inverting terminal IN-. The non-inverting and inverting equivalent resistances are constant and independent of the test voltage (VIN). RSENSE includes several series resistors that provide multiple orders of magnitude in impedance selection. For example, if 10Ω is required, the terminal is IN + and "B" near IN-1 (points A, C, and D are not connected). For high power loads, pay attention to the rated power of the sense resistor and nFET. The power supply of the operational amplifier can be a battery or any other DC power supply. Its maximum working current is only 20 μA. It is powered by a 9V battery. Under normal circumstances, the active load can be used for 1-2 years.X One Question Related to Variable Resistors10.1 QuestionVolume control regulator in a CD receiver, radio and amplifier also useA.transistorB.variable resistorC.thermistorD.fixed resistor10.2 AnswerB  XI FAQ1. What is a variable resistor do?A variable resistor gives the user more control over the resistance, as it allows for variance or for the resistor to be changed in order to meet the resistance requirements of the user. Changing the resistance as a user is actually very simple. 2. What are the two types of variable resistors?The different types of variable resistors include Potentiometer. Rheostat. Thermistor. 3. What is the difference between a variable resistor and a potentiometer?In the potentiometer, the resistance of the track remains the same as the wiper moves and only the potential on the wiper changes. In a variable resistor, the resistance of the track apparently changes as the wiper moves and short circuits more or less of the track resistance. 4. What is the advantage of a variable resistor?The advantage of variable resistors is that you have more control over the voltage. You can also adjust the amount of voltage flowing through a circuit. 5. What is the symbol of a variable resistor?A variable resistor also called an adjustable resistor, consists of two terminals, where one of the terminals is a sliding or moving contact often known as a wiper. The variable resistor IEC symbol is represented by a rectangular box and an arrow across (or above) it, like that shown in the figure below. 6. How do you identify a variable resistor?The variable resistor is represented by a zig-zag line and an arrow across (or above) it, like that shown in the figure below. 7. How many types of variable resistors are there?Variable resistors can be categorized into three types: Potentiometers. Rheostats. Digital potentiometers. 8. Is LDR a variable resistor?An LDR is a component that has a (variable) resistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits. 9. Do variable resistors have polarity?Resistors are blind to the polarity in a circuit. Thus, you don't have to worry about installing them backward. Current can pass equally through a resistor in either direction. 10. Why is a variable resistor needed in a circuit?Simply put, a variable resistor is able to have its electrical resistance adjusted. These devices are used when working with electrical circuitry because they help to control voltage and/or currents. They specifically work with voltage and currents that are a part of the circuit. 

Ⅰ IntroductionIn electronics, the transient interference of voltage and current source is the main cause of damage to circuits and equipment, and it often causes immeasurable losses to the society. These disturbances usually come from the  the starting and stopping operation of power equipment, instability of the AC grid, lightning interference and electrostatic discharge, etc. They are almost ubiquitous and always present. Therefore, scientists have developed a high-efficiency circuit protection device TVS to effectively suppress transient interference.TVS (transient voltage suppressor) is a new product developed on the basis of Zener diode technology. Its circuit symbol is the same as that of ordinary Zener diode. As a common circuit protection component, it is widely used in various fields: automotive electronics, consumer electronics, power drives, industrial power distribution, renewable energy, telecommunications, home appliances, measuring instruments, medical electronics, industrial control, lighting, security systems, building control and automation, audio / video equipment, computers, etc. Learn more about tvs diode, let's check the following transient voltage suppressor tutorial. TVS Diode Tutorial: Transient Voltage SuppressorCatalogⅠ IntroductionⅡ Terminology2.1 Basic Characteristics2.2 Electrical Characteristics2.3 Main ParametersⅢ TVS SelectionⅣ TVS vs Varistor, CapacitorⅤ Application Examples5.1 Lighting Protection5.2 Transistor Protection5.3 Electric Relay Protection5.4 Silicon Control Protection5.5 Integrated Op Amp Protection5.6 Integrated Circuit (IC) Protection5.7 Microcomputer System Protection5.8 DC Regulated Power Supply Protection5.9 Suppression of Electromagnetic Pulse Interference Ⅱ Terminology2.1 Basic CharacteristicsTVS diode, under the specified reverse application conditions, when subjected to a high-energy transient overvoltage pulse, due to it has a very fast response time (sub-nanosecond) and a very high  surge absorption ability, its working impedance can be immediately reduced to a very low on value, allowing large currents to pass, and clamping the voltage to a predetermined level, thereby effectively protecting precision components in electronic circuits from damage. TVS can withstand instantaneous pulse power up to kilowatts, and its clamp response time is only 1ps (10-12S). The forward surge current allowed by TVS can reach 50 ~ 200A under the conditions of TA = 250C and T = 10ms.TVS diodes work similarly to common Zener diodes. If the breakdown voltage is higher than the mark, the TVS diode will conduct. Compared with the Zener diode, the TVS diode has a higher current conduction capability. When the two poles of a TVS diode are subjected to reverse transient high-energy shocks, the high impedance between the two poles of the TVS diode becomes low at a speed of the order of 10 ^ -12S, while absorbing surge power of up to several kilowatts. The clamped voltage between the two poles is at a safe value, which effectively protects precision components in electronic circuits from being damaged by surge pulses. Figure 1. Working Characteristic Curve of TVS DiodeWhen the reverse voltage of the two poles of the TVS is greater than the maximum reverse voltage, it starts to conduct reversely; after the reverse voltage is greater than the breakdown voltage, it begins to be broken down, while the current starts to change suddenly; when the reverse voltage is greater than the maximum clamping voltage, the tube is in an avalanche breakdown state. At this time, the current flowing through the tube increases sharply, and the voltage difference across the tube does not change much (the voltage is clamped).Under specified reverse application conditions, the TVS diode will provide a low-impedance path, and the instantaneous current flowing to the protected component will be shunted to the TVS diode through a large current method, while the voltage across the protected component will be limited to the clamping voltage of TVS. When the overvoltage condition disappears, the TVS diode returns to a high impedance state.  Note: Unidirectional and Bidirectional TVS DiodesUnidirectional TVS SymbolBidirectional TVS Symbol1) Look at the signs: for unidirectional tvs diode, there is a thin color ring, connected to the positive electrode, and for bidirectional tvs diode, there are two rings in the middle, or there is no sign, no polarity.2) Look at the specifications: bidirectional tvs is bidirectional conduction, and unidirectional tvs is unidirectional conduction.3) Look at the model: The model name of the tvs tube is regular, and most of the tvs diode models can see the parameters on the case. For details, it is necessary to consult the manufacturer.4) Using multimeter tool: the unidirectional has voltage, while avalanche breakdown characteristics are available on the DC side; voltage is on both sides, and the DC side is symmetrical on both sides.Bidirectional tvs diodes can absorb instantaneous large pulse power in both forward and reverse directions and clamp the voltage to a predetermined level. In addition, bidirectional TVS is suitable for AC circuits, and unidirectional TVS is generally used for DC circuits. 2.2 Electrical Characteristicsa. Unidirectional TVS (V-I characteristic) Figure 2. Unidirectional TVS DiodeThe unidirectional tvs diode has the same forward characteristics as ordinary Zener diodes, and the reverse breakdown inflection point is approximately “right angle” as a hard breakdown and is a typical PN junction avalanche device. The curve segment from the breakdown point to the VC value indicates that when there is a transient overvoltage pulse, the current of the device increases sharply while the reverse voltage rises to the clamped voltage value and remains at this level.b. Bidirectional TVS (V-I characteristic) Figure 3. Bidirectional TVS DiodeThe V-I characteristic curve of the bidirectional tvs diode is similar to the two back-to-back unidirectional tvs diodes combination. Its forward and reverse directions have the same avalanche breakdown characteristics and clamping characteristics. The symmetry relation of the breakdown voltage on both sides of the positive and negative is as follows: 0.9≤ VBR(positive)/(inverse) ≤1.1, once the interference voltage at both ends of it exceeds the clamping voltage will be immediately suppressed, thus the bidirectional tvs are very convenient for ac loop application.  2.3 Main Parameters1) breakdown voltage V(BR)In the region where the device breaks down, the voltage across the device is measured at the specified test current I (BR), which is called the breakdown voltage. In this area, the tvs diode becomes a low impedance path.2) maximum reverse pulse peak current IPPIn reverse operation, IPP refers to the maximum pulse peak current allowed by the device under specified pulse conditions. The product of IPP and the maximum clamping voltage VC (max) is the maximum value of the transient pulse power.The TVS should be properly selected during use, so that the rated transient pulse power PPR is greater than the maximum transient surge power that may occur in the protected device or wires.When the instantaneous pulse peak current appears, the TVS is broken down and its breakdown voltage value rises to the maximum clamping voltage value. As the pulse current decreases exponentially, the clamping voltage also decreases and returns to the original state. Therefore, TVS diode can suppress the impact of possible pulse power to effectively protect the electronic circuits.The test waveform of the TVS peak current uses a standard wave (exponential waveform), which is determined by TR / TP.Peak current rise time TR: The time from when the current reaches 0.9 IPP from 0.1 IPP.Half-peak current time TP: The time after the current passes through the maximum peak from zero and then drops to 0.5 IPP.The TR / TP values of typical test waveforms are listed below:A. EMP wave: 10ns / 1000nsB. Lightning wave: 8μs / 20μsC. Standard wave: 10μs / 1000μs3) Maximum reverse working voltage VRWMWhen the device operates in reverse, the voltage across the device is called the maximum reverse operating voltage VRWM under the specified IR, usually VRWM = (0.8 ~ 0.9) V(BR). At this voltage, the power consumption of the device is small. When used, VRWM should not be lower than the normal working voltage of the protected device or circuits.4) Maximum clamping current VC(max)The maximum voltage value across the device under the peak pulse current IPP is called the maximum clamping voltage. When used, VC (max) should not be higher than the maximum allowable safe voltage of the protected device. And the ratio of the maximum clamping voltage to the breakdown voltage is called the clamping coefficient.Clamping coefficient = VC(max) / V(BR), the general clamping coefficient is about 1.3.5) Reverse pulse peak power PPRThe PPR of TVS depends on the pulse peak current IPP and the maximum clamping voltage VC (max). In addition, it is also related to the pulse waveform, pulse time and ambient temperature.When the pulse time Tp is constant, PPR = K1‧K2‧VC (max) ‧IPP(K1 is the power coefficient, and K2 is the temperature coefficient of the power) The typical pulse duration tp is 1MS. When the pulse time tp applied to the transient voltage suppression diode is shorter than the standard pulse time, its peak pulse power will increase as tp is shortened.Figure 4. Peak Pluse Power vs Pluse TimeTVS reverse pulse peak power PPR is related to the pulse waveform subjected to surge, expressed by the power coefficient K1: E=∫i(t)‧V(t)dt     i (t) is the pulse current waveform, and V (t) is the clamping voltage waveform.This rated energy value is not reproducible to TVS in a very short time. However, in practical applications, surges often occur repeatedly. In this case, even if the single pulse energy is much smaller than the pulse energy that the TVS device can withstand, if repeat, these single pulse energy will accumulated, in some cases, it will exceed the pulse energy that the TVS device can withstand. Therefore, the circuit design must carefully consider and select the TVS device, so that the accumulation of pulse energy repeatedly applied within the specified interval does not exceed the pulse energy rating of the TVS device.6) Capacitance CPP  Figure 6. The Capacitance of TVS CircuitThe capacitance of TVS is determined by the area of the silicon sheet and the bias voltage. In the case of zero bias, the capacitance value decreases with the increase of the bias voltage. The value of the capacitance will affect the response time of the TVS device.7) Leakage current IRWhen the maximum reverse working voltage is applied to the TVS, the TVS tube has a leakage current IR. When the TVS is used in a high impedance circuit, the leakage current is an important parameter. In practice, especially in automotive electronics, this parameter affects static current.  Ⅲ TVS SelectionWhen selecting tvs diode, the specific conditions of the circuit must be considered, and generally the following principles should be followed:1) The clamping voltage VC (max) is not greater than the maximum allowable safe voltage of the circuit.2) The maximum reverse working voltage VRWM is not lower than the maximum working voltage of the circuit. Generally, VRWM can be selected to be equal to or slightly higher than the maximum working voltage of the circuit.3) The rated maximum pulse power must be greater than the maximum transient surge power present in the circuit. Ⅳ TVS vs Varistor, Capacitor1) TVS diode and varistor do not have switching characteristics like switching elements, but have voltage regulation characteristics like zener diodes.2) The varistor can withstand a larger surge current, and the larger the varistor can withstand the larger surge current, which can reach tens of kA to hundreds of kA at the maximum; but the non-linear characteristics of the varistor are poor and the limiting voltage is higher at large current, and the leakage current is larger at low voltage.3) The non-linear characteristics of TVS diodes are the same as those of Zener tubes. Leakage current before breakdown is very small. After the breakdown, it is in a standard voltage stabilization. Compared with varistors, the maximum clamping voltage of TVS diode is smaller, but its current capability is poor than a varistor. Since the breakdown voltage VBR and the clamping voltage VC of the varistors are relatively high, the current flow capability is relatively strong, and the surge pulse absorption capability is stronger, so it is more suitable for ESD or surge protection of the power interface.4) For the reaction speed, the response speed of the TVS is fast (ps level), while the varistor’s is slow ( ns level). In addition, the capacitance of both is large (ps: TVS also have low capacitance products).5) The TVS tube has high reliability, and a long service life, while the varistor has poor reliability, easy aging and short service life.Other ViewCompared with ceramic capacitors, TVS diodes can withstand a voltage of 15 kV, but ceramic capacitors have a lower ability to withstand high voltages. A 5 kV shock will cause about 10% of the ceramic capacitor to fail, and by 10 kV, its damage rate will reach 60%. Ⅴ Application Examples5.1 Lighting ProtectionIn thunderstorm-prone areas, lightning-induced voltage often breaks down some of the integrated circuits in a computer network. The reason is that cables are damaged due to transient high voltage caused by lightning induction, by installing tvs diodes in the microcomputer, it is useful to reduce damages and commercial loss. And the result shows that it is very practical, and it can improve the reliability of the whole machine application.TVS also have many other applications, for example, for VMOS high power transistors, the tvs diodes between the gate and the source and the machine can prevent gate breakdown and improve the reliability of the VMOS power tube application. 5.2 Transistor ProtectionVarious transient voltages can cause damage to the EB junction or CE junction of the transistor. Especially when the collector of the transistor has an inductive load (coil, transformer, motor), a high-voltage back-EMF can be generated, which often causes the transistor to be damaged. It is necessary to use a tvs diode as a protector. 5.3 Electric Relay ProtectionRelay contacts often use large currents to switch on and off high-current inductive loads such as motors, and the inductor has a high back electromotive force when switching, and has a large amount of energy. What’s more, the contacts are burned or broken to produce an arc, and the surge current generated by the arc is very large. To protect the contacts by suppressing the occurrence of arcs to protect the relays, adding a tvs diode is more effective. In the past, a capacitor or a capacitor series resistor, a diode or a diode series resistor and other suppression methods were used. 5.4 Silicon Control ProtectionThe thyristor may has wrong trigger and cause malfunction. The control electrode current cannot be too large and the voltage cannot be too high, in order to do it, TVS can be used for protection. 5.5 Integrated Op Amp ProtectionIntegrated op amps are very sensitive to external electrical stress. In the process of using op amps, if having excessive voltage or current due to operating errors or abnormal working conditions, especially surges and electrostatic pulses, it is easy to damage the op amp. In the integrating circuit, if the capacitor is charged and discharged to a high potential, and then the power supply voltage is cut off, a transient voltage will be generated at the input terminal, and a large discharge current will occur, resulting in damage to the operational amplifier. At this time, tvs protection method adopted at the input terminal of op amp to avoid device damage. If the capacitance value is large (such as greater than 0.1μF), the protecting effect will be very significant. 5.6 Integrated Circuit (IC) ProtectionAs integrated circuits become more integrated, their withstand voltages are getting lower and lower, and they are easily damaged by transient voltages. Protective measures must be taken, for example, adding tvs diode in the circuit, the CMOS circuit has a protection network at its input and output ends. 5.7 Microcomputer System ProtectionIn a typical microcomputer system, various interference or transient voltages entering through the power line, input line, and output line may cause the microcomputer to malfunction and fail, especially from the switching power supply. The on-off motor near the microcomputer, voltage surges and transients of AC power, electrostatic discharges, etc. may cause the system to fail, and in severe cases may damage the device. Connecting the tvs diode to the input and output lines of the power supply of the microcomputer can prevent the transient voltage from entering the “microcomputer” bus, strengthen the microcomputer's resistance to external interference, ensure the normal operation, and improve its reliability. 5.8 DC Regulated Power Supply ProtectionA DC regulated power supply with a transistor that expands the current output, adding a tvs diode to its regulated output can protect the equipment, and can also absorb peak voltage from the collector to the emitter in the circuit to protect the transistor. In a word, adding a tvs diode at the output end of each voltage stabilization source can greatly improve the reliability of the whole operation. 5.9 Suppression of Electromagnetic Pulse InterferenceA nuclear explosion will cause a strong electromagnetic pulse, which causes induced voltage in the wire. If the induced voltage exceeds the breakdown voltage of the device, it may cause the breakdown of the component, especially for long-term transmission, it is more easily to cause high voltage.TVS diodes are connected in parallel to the signal and power lines, which can absorb the induced voltage caused by electromagnetic pulses, ensure the reliability of the system, and avoid radiation damage to components. Frequently Asked Questions about Transient Voltage Suppression Diode1. How does a transient voltage suppressor work?Transient Voltage Suppressor Diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy of the overvoltage event, and then it automatically resets after overvoltage condition. 2. What does a transient suppressor do?A transient voltage suppressor or TVS is a general classification of an array of devices that are designed to react to sudden or momentary overvoltage conditions. ... This makes TVS devices or components useful for protection against very fast and often damaging voltage spikes. 3. What is a transient voltage surge suppressor?A transient voltage surge suppressor is a device which is installed on an AC or DC power line to act as a cutoff if there is a momentary surge of electrical power, also known as a “transient.” TVSS devices are considered crucial to the protection of sensitive equipment which would result in circuitry damage or data. 4. What is a voltage transient?A transient voltage is a temporary unwanted voltage in an electrical circuit that range from a few volts to several thousand volts and last micro seconds up to a few milliseconds. ... Faulty contactors and lightning are the most common source of transients. 5. How does a transient voltage suppressor diode work?Transient Voltage Suppressor Diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy of the overvoltage event, and then it automatically resets after overvoltage condition. 6. Which device can be used as a transient suppressor?Transient voltage suppression diodeOne such common device used for this purpose is known as the transient voltage suppression diode that is simply a Zener diode designed to protect electronics device against overvoltages. 7. What does a suppression diode do?A transient-voltage-suppression (TVS) diode, also transil or thyrector, is an electronic component used to protect electronics from voltage spikes induced on connected wires. 8. What is the difference between Zener and TVS diode?Zener diodes are used to make the voltage more stable. They act as a regulator as well as a protective device. TVS diode is intended to prevent high voltage transients such as Surge and ESD damaging. 9. Where are transient voltage most dangerous?Transient voltages are most dangerous while taking measurements on equipment. Should someone turn something off it could cause a transient voltage spike. 10. What is transient protection?Transients (momentary spikes in voltage or current) can disrupt or damage the products connected to signal or power lines. The most common transient protection schemes limit the voltage amplitude, current amplitude or transition times on the circuit they are protecting.