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CatalogⅠ IntroductionⅡ The Layout of the Car MarketⅢ The Layout in the Industrial FieldⅣ The Layout on the Internet of ThingsⅤ ConclusionⅠ IntroductionON Semiconductor: In 2021, it will focus on the automotive, industrial and cloud power, and the Internet of Things marketThe end of the year and the beginning of the year is often a time for companies to make summaries and outlook, and the semiconductor industry is no exception. Not long ago, ON Semiconductor also made a year-end review of 2020 and revealed to the media what ON Semiconductor plans to do in 2021. "The year 2020 is a year of surprises for everyone. People around the world are experiencing the worst epidemic in a century. The good news is that the epidemic has eased in some parts of the world. Looking forward to 2021, we hope to get out of the epidemic as soon as possible and have a more favorable business environment." DavidSomo, senior vice president of strategy, marketing and solution engineering at ON Semiconductor, said in his opening remarks at the press conference.Due to the epidemic, the global economic situation in 2020 is not optimistic. According to Bloomberg data, GDP growth in 2020 is expected to drop from 2.8 percent in 2019 to minus 3.7 percent. China will be the only major economy in the world with positive growth by 2020, while all other economies are expected to suffer single-digit declines. Fortunately, in the second half of 2020, the global economy began to recover. As indicated by the PMI (Purchasing Managers' Index), manufacturing activity in all major economies resumed growth in the second half of the year, with the only exception being Japan, which also showed a positive trend. DavidSomo expressed an optimistic outlook for the global economy in 2021. "We expect that the economic outlook for next year will be positive, significantly better than this year, and there is a consensus for overall GDP growth of around 5% in 2021," he said. He also stressed that, for its part, ON Semiconductor wants to be a reliable supplier of power, analog, sensor and connection solutions, enabling innovation in energy-efficient electronics. It will focus on providing comprehensive solutions to global customers in the automotive, industrial and cloud power markets, as well as the Internet of Things market. Ⅱ The Layout of the Car MarketIn the automotive sector, ON Semiconductor implements a comprehensive sensor product and solution layout, including image sensors, radar, lidar, ultrasonic sensors and other products and solutions. In additon to sensors, R&D resources continue to be invested in silicon and silicon carbide power semiconductors, as well as LED lighting and automotive power management products. Those investments have also paid off handsomely, accounting for 33% of ON Semiconductor's $5.5 billion in 2019 revenue. DavidSomo pointed out that in the future, ON Semiconductor will continue to develop new products in the automotive market and increase investment in research and development. "On the automotive side, we will push forward research and development around sensors, autonomous driving-related applications, new energy vehicles, and the electrification of vehicles." He revealed. ON Semiconductor is one of the top 10 semiconductor suppliers in the automotive industry. DavidSomo proudly states, "Since entering the automotive market in 2010, ON Semiconductor has shipped 130 billion chips to automotive customers by 2019. In 2019, there were more than 230 ON Semiconductor devices used in every vehicle produced worldwide."The company has set the industry standard for automotive image sensors, with more than 120 million of them shipped to Advanced Driver Assistance System (ADAS) applications. Over the past 13 years, more than 400 million ON Semiconductor automotive image sensors have been used in vehicles on the road. ON Semiconductor has developed a complete portfolio of product solutions and sensor modes to support L4 and L5 autonomous vehicles, including ultrasonic sensor interfaces, image sensors, solid-state LIDAR and millimeter-wave radar technologies. DavidSomo said that ON Semiconductor's MMW technology, acquired from IBM Research Group in Sea Law (IBM), has been used in communications and fiber optics, and plans to use the technology in the automotive sector. It is currently being tested with customers for prototypes but has not yet been used in commercial automotive production. In the case of LiDAR, the technology came from the acquisition of sensL to acquire technology on solid-state LiDAR. According to DavidSomo, sensL was originally designed for use in the medical market but is now being developed for use in the automotive market. "Multiple customers have incorporated our Silicon Photomultiplier (SiPM) and Single-Photon Avalanche Diode (SPAD) technologies into solid-state lidar systems, enabling commercial lidar applications in the automotive industry for L2+ and L3 level autonomous driving safety applications." He went on to point it out. On the cost side, DavidSomo says that because ON Semiconductor's lidar solution is a solid-state solution, it has been able to bring the cost of lidar down from more than $1,000 for mechanical rotation in the past to the current $500 range for solid-state solutions. In terms of image sensors, over the years, ON Semiconductor has made three acquisitions, including Aptina, Cypress's image sensor technology and TrueSense, to enrich its image sensor portfolio.Ⅲ The Layout in the Industrial FieldDavidSomo said that ON Semiconductor offers a wide range of power and automation solutions in the industrial and cloud power markets that support different application scenarios. In terms of power semiconductors, in 2018, ON Semiconductor ranked second behind Infineon with a market share of about 9 percent, according to IHS. As an example, he pointed out that powering the cloud requires several processes, including generation, power supply and power demand management. "In these processes, we have a complete silicon and silicon carbide technology portfolio that supports power generation, transmission and distribution, as well as power and demand management for data centers and 5G base stations." He points it out. In terms of energy efficiency improvement, the use of ON Semiconductor's cloud power solution increased energy efficiency by about 0.5%. In a typical VL data center, the savings over the life of the system are estimated at approximately $38 million. The energy efficiency improvement is only 0.5%, which may not sound like much, but when measured at the system-wide level of deployment, the savings over the lifetime of the system are significant. The development of energy infrastructure is also unstoppable, as a society and the government further promote the development of new energy sources and shift more from coal-fired power generation to renewable energy sources such as wind and solar power. In order to save energy and reduce emissions, reduce air pollution, from fuel vehicles to new energy vehicles, which has generated the demand for electric vehicle charging pile, and ON Semiconductor silicon and silicon carbide power discrete devices and modules, can support the construction of electric vehicle charging pile. Similarly, its power technologies, such as solar inverters used in solar panels, enable clean energy generation, and "ON Semiconductor is fortunate to partner with customers in China to develop applications in these areas." DavidSomo said. Manufacturing is also one of the biggest users of energy. In the United States, our power solutions are used in plant motor drive systems, resulting in savings of more than $350 million per year. If applied globally, the potential savings could reach approximately $5.8 billion per year, resulting in energy efficiency improvements in manufacturing motor drive systems.Ⅳ The Layout on the Internet of ThingsIn the Internet of Things (IoT) area, ON Semiconductor has a complete set of key components and modules that enable devices to be connected, intelligent, aware and actuated in their operating environment."Of course, we recognize that our semiconductor components are not sufficient to build the end-to-end connected Internet of Things (IoT) systems that our customers need, so we are investing more to accelerate development and provide our customers with a number of development tools to enable faster application development and market deployment." DavidSomo admits. While ON Semiconductor can provide many of the key building blocks, DavidSomo believes it is important to work with partners in the Internet of Things (IoT) ecosystem to build IoT solutions for secure end-to-end connectivity. As shown in the figure below, ON Semiconductor works with a number of technology partners to enhance the performance of IoT devices developed by clients, as well as with infrastructure providers such as cloud service providers to enable edge devices to connect securely and stably to the cloud. He also revealed that the company is focusing on three vertical areas in the Internet of Things, namely asset tracking and monitoring, connected lighting, and smart homes and building automation.Ⅴ ConclusionIn conclusion, DavidSomo said that in the process of semiconductor device manufacturing, ON Semiconductor also recognizes the growing need to provide its customers with complete system solutions that add value. As a result, ON Semiconductor offers modular products for power components and built-in controls, as well as reference design kits to speed up customer product development. ON Semiconductor also provides software and design tools to help customers complete designs faster and get their equipment to market faster. He also stressed that ON Semiconductor will focus on research and development, and is committed to developing innovative products and solutions including power, simulation, sensors and connectivity solutions. "Through both endogenous growth and exogenous acquistions, we are further enhancing our capabilities to support the applications our customers are developing, while also building our professional application capabilities to help them develop products better and faster to market."

IntroductionIn electronics, what is clipper? A circuit which removes the peak of a waveform is known as a clipper. Clipper circuit is designed to prevent a signal from exceeding a predetermined reference voltage level. The clipper circuit can be designed by utilizing both the linear and nonlinear elements such as resistors, diodes, or transistors. The diode clipper, also known as a diode limiter, is a wave shaping circuit that limits positive or negative amplitude, or both. In electronics, diode clipper circuits are commonly used to process various signals. It is is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. Clipping changes the shape of the waveform and alters its spectral components.Clipper Circuits IntroductionCatalogIntroductionⅠ Clipper Circuit Types1.1 Positive Clipper Circuit1.2 Negative Clipper Circuit1.3 Combinational Limiter CircuitⅡ Clipper Circuits Analysis2.1 Clipper Circuit Structure2.2 Clipper Circuit ProblemsⅢ General Forms of Clipper Circuits3.1 Clipper Circuit Description3.2 Common Clipper Circuit ExamplesⅠ Clipper Circuit TypesDiode clipper is a limiting circuit which limits the output voltage. In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A basic diode limiter circuit is composed of a diode and a resistor. It is divided into three types: positive clipper circuit, negative clipper circuit and combinational clipper circuit. The positive clipper circuit produces a clipping effect when the input voltage is higher than a certain upper limit value; the negative clipper circuit produces a limit effect when the input voltage is lower than a certain lower limit value; the combinational clipper circuit produces a limit effect when the input voltage is too high or too low. In a positive clipper, the positive half cycles of the input voltage will be removed. During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. The clipper circuits are described as following.1.1 Positive Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the positive portions of the waveform. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. In following figure, when the input signal voltage is lower than a preset upper limit voltage, the output voltage will change with the input voltage, however, when the input voltage reaches or exceeds the upper limit, the output voltage will remain at a fixed value, so that the signal amplitude is limited at the output.1.2 Negative Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the negative portions of the waveform, is termed as negative series clipper. For the figure below, the diode is series to the input and output. If the diode has ideal switching characteristics, when iu is lower than E, D will not conduct, ou=E; when ui is higher than E, D will conduct, ou=iu. The limiting characteristic of this limiter circuit is shown in the figure.1.3 Combinational Limiter CircuitThis kind of circuit combines the positive and negative limiters together which shows in the following figure. Ⅱ Clipper Circuits Analysis2.1 Clipper Circuit StructureIn the circuit, Al is an integrated circuit (a common component), VT1 and VT2 are transistors, Rl and R2 are resistors, and VDl to VD6 are diodes.Analyzing the effect of VD1 and VD2 in the circuit mainly explains the following points.1) It can be seen from the circuit that the circuit structure of the two groups of diodes are the same. Both play the same role in this circuit, so the working principle of them are the same.2) The pin ① is connected to the base of the transistor VT1 through a resistor Rl. Obviously Rl is a signal transmission resistor. The signal output on the pin ① is added to the base of VT1 through Rl (there is no DC blocking capacitor between pin ① and VT1). From this circuit structure, it can be judged that the pin ① is an output signal pin, and it outputs a composite signal of DC and AC. The purpose of determining that the pin ① is to figure out the specific function of the diode VD1 in the circuit.3) The DC voltage output by pin ① is not high enough to make the external diode in a conducting state. The analysis is: if the DC voltage output by the pin ① is high enough, then VD1, VD2 and VD3 conduct, and the internal resistance becomes small. This will shunt the AC signal output by the pin ① to the ground, so the signal will be attenuated. However, this circuit does not need such attenuation. Therefore, the conclusion drawn from this: VD1, VD2 and VD3 are not turned on by pin ① DC voltage output.4) The output from pin ① is the superimposed signal of DC and AC, which is added to the base of the transistor VT1 through the resistor Rl. VT1 is an NPN transistor. If the amplitude of the positive half-cycle AC signal added to the base of VT1 is very large, which may burn the VT1. When the negative half-cycle signal added to the base of VT1 is large, which has no effect on VT1, because the negative signal on the base of VT1 reduces current.Follow the above circuit analysis, it can be judged that VD1, VD2, and VD3 in the circuit has clipper function, to prevent VT1 from burning out. 2.2 Clipper Circuit ProblemsIn the figure, Ul is the DC voltage in the output of pin ①, U2 is the limiting voltage value.When the AC voltage in the output signal of pin ① is relatively small, the positive half cycle of the AC signal plus the DC output voltage does not make the VD1, VD2 and VD3 conduction. Therefore, all diodes are cut off, which has no effect on the AC signal output by pin ①. Assuming that the positive half-cycle output AC signal by pin ① is very large during a certain period, as shown in the signal waveform, at this time it plus the DC voltage can conduct VD1, VD2 and VD3. If the conduction voltage of each diode is 0.7V, then three diodes is 2.1V. Since the tube voltage drop after conduction is basically the same, that is, the maximum voltage of pin ① is 2.1V. So the excess part of the positive half cycle of the AC signal is limited by the resistor. When the DC and AC output signals at pin ① is less than 2.1V, diodes will not conduct and keep cutoff state, which has no clipping effect on the signal.For the specific details of clipper circuit, there are several explanations as follows.1) The negative half cycle large signal output by the pin ④ will not cause VT1 overcurrent, because it will decrease the base voltage of the NPN transistor and the base current, so there is no need to add the limiter circuit.2) The one-way limiter circuit mentioned above, it can only limit the large signal part of the positive or negative half of the signal, and does not limit the signal in the other half. The other is the combinational limiter circuit, which can limit the positive and negative half-cycle signals at the same time.3) There are many reasons for the abnormal increase of the signal amplitude. For example, the fluctuation of the power supply voltage cause it to increase a lot at a certain moment, and the large-scale interference pulse from the outside into the circuit also causes a certain increase.4) After the three diodes VD1, VD2 and VD3 conduct, the sum of the DC and AC voltages on pin ① is 2.1V. This voltage added to the base of VT1 through resistor Rl is maximum, so as to the current of VT1.5) Since the pin ① is the same as the external circuit of pin ②, the working principle of the limiter circuit is the same. So only one circuit needs to be analyzed when analyzing the circuit.6) According to the characteristics of the series circuit, the current in the series circuit is equal everywhere. It can be known that the three series diodes VD1, VD2 and VD3 are turned on at the same time, or they will be turned off at the same time. Therefore, in the series circuit, a diode is turned on and other diodes are turned on.Ⅲ General Forms of Clipper Circuits3.1 Clipper Circuit DescriptionThere are two types of clippers namely series and parallel. In series clipper, diode is connected in series with the load. In parallel clipper, diode is in parallel to the load.1) Series clippers: if the diode is connected in series with load resistanceUnbiased series clipper: in that case the circuit diode is connected in series with load resistance and no external voltage is applied to the circuit.+ve unbiased series clipper: if the +ve portion of output is clipped its called +ve unbiased series clipper.-ve unbiased series clipper: if the -ve portion of output is clipped its called +ve unbiased series clipper.Biased series clipper: if in the circuit, diode is connected in series with load resistance and external voltage is applied to the circuit+ve biased series clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve biased series clipper: if the -ve portion of output is clipped its called +ve biased series clipper.2) Parallel clippers: if the diode is connected in parallel with load resistanceUnbiased parallel clipper: in that case the circuit diode is connected in parallel with load resistance and no external voltage is applied to the circuit.+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve unbiased parallel clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve unbiased parallel clipper.Biased parallel clipper: if in the circuit, diode is connected in parallel with load resistance and external voltage is applied to the circuit+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve biased series clipper. 3.2 Common Clipper Circuit ExamplesIn general, clippers circuit are classified into two types: Series Clippers, Shunt Clippers, and Dual (Combination) Clippers.Series Clipper: The diode is connected in series with the load resistance. 👇Figure 1. Series Positive ClipperThe positive amplitude waveform is cut, and the negative amplitude waveform is retained, as follows:Figure 2. Series Positive Clipper with Positive BiasThe positive amplitude waveform is cut, and the offset positive voltage is retained on the negative amplitude waveform, as follows:Figure 3. Series Positive Clipper with Negative BiasThe waveform of positive amplitude is cut, and the negative voltage is shifted based on the waveform of negative amplitude, as follows:Figure 4. Series Negative ClipperThe negative amplitude waveform is cut, and the positive amplitude waveform is retained, as follows:Figure 5. Series Negative Clipper with Positive BiasThe negative amplitude waveform is cut, and the positive voltage is offset on the positive amplitude waveform, as follows:Figure 6. Series Negative Clipper with Negative BiasThe negative amplitude waveform is cut, and the negative voltage is offset on the positive amplitude waveform as follows: Shunt Clipper: Diode is in parallel with load resistance in circuit. 👇Figure 7. Shunt Positive ClipperFigure 8. Shunt Positive Clipper with Positive BiasFigure 9. Shunt Positive Clipper with Negative BiasFigure 10. Shunt Negative ClipperFigure 11. Shunt Negative Clipper with Positive BiasFigure 12. Shunt Negative Clipper with Negative Bias Dual (Combination) Clipper: It is desired to remove a small portion of both positive and negative half cycles. 👇Figure 13. Combination ClipperWhen the positive and negative waveforms must be limited, a combinational limiter circuit is required, as follows:Images Reference: Clipper Circuits - Series Clipper, Shunt Clipper, and Dual Clipper Frequently Asked Questions about Diode Limiter and Clipper Circuit1. What is Clipper and clamper?The major difference between clipper and clamper is that clipper is a limiting circuit which limits the output voltage while clamper is a circuit which shifts the DC level of output voltage. ... While clamper is used when we need multiples of the input voltage at the output terminal. 2. What is the function of clipper circuit?In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A clipper does not distort the remaining part of the applied waveform. 3. What is Clipper circuit and its types?A clipper is a device which limits, remove or prevents some portion of the wave form (input signal voltage) above or below a certain level, in other words, the circuit which limits positive or negative amplitude ,or both is called chipping circuit. The clipper circuits are of the following types. Series positive clipper. 4. What is the difference between a positive clipper and a negative Clipper?Positive Clipper and Negative Clipper. In a positive clipper, the positive half cycles of the input voltage will be removed. ... During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. 5. How does diode clipping work?The Diode Clipper, also known as a Diode Limiter, is a wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together. This clipping of the input signal produces an output waveform that resembles a flattened version of the input. 6. What is the main purpose of a diode limiter?The diode limiter also called Clipper as it is used to limit the input voltage. A basic diode limiter circuit is composed of a diode and a resistor. Depending upon the circuit configuration and bias, the circuit may clip or eliminate all or part of an input waveform. It limits the output voltage to a specific value. 7. What is the purpose of a clamping diode?The clamping circuit fixes the voltage lower limit to zero, that is, the start of the signal is 0 V. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. 8. What is a diode clamping circuit?A clamper circuit shifts the DC level or the reference level of the signal to the desired level without changing the shape of the waveform. The clamper circuit can be designed using the diode, resistor, and the capacitor.

IntroductionSemiconductor diode, also known as crystal diode, has obvious unidirectional conductivity. It is a kind of electronic components widely used in electrical equipment for protection, rectification, switching, and many other applications. So it is pretty common to see diodes in daily electronic circuits, such as Zener diodes, light-emitting diodes, photodiodes, etc. Therefore, it is necessary to know how to test whether a diode is properly working or not.How to Test a Diode Using a MultimeterCatalogIntroductionⅠ Diode Basics1.1 To Figure Out Diode Anode and Cathode1.2 What Would Cause a Diode to Fail?1.3 Common Diode Failures AnalysisⅡ How to Test Diode with a Multimeter?2.1 Digital Multimeter and Analog Multimeter2.2 Common Diodes Testing Rules2.3 Testing Methods of Types of DiodesⅢ Example Analysis3.1 Test a Diode in Circuit3.2 Power-off and Power-on Testing Methods3.3 ConclusionⅠ Diode Basics1.1 To Figure Out Diode Anode and CathodeThe anode and cathode of diode can be distinguished by screen printing on PCB board, which are as shown in the following:1) The notched end is the cathode of diode.2) The end with a horizontal bar is the cathode.3) The end with white parallel bars is the cathode.4) One end of the triangle arrow is the cathode.5) The small end of the plug-in diode is the cathode, and another big end is the anode.1.2 What Would Cause a Diode to Fail?The common reasons for a diode failure are open circuit, short circuit and unstable voltage regulation. Among these three types of failures, there may be signs. For example, the power supply voltage rises, the supply voltage drops to zero or the output is unstable. Therefore, specific problems must be analyzed in detail for the diode test.The common measurement tool for diode is a multimeter, including on-circuit measurement (the diode is on the circuit board) and off-circuit measurement (the diode is not on the circuit board). As for the basic principle of diode measurement, the forward resistance and the reverse resistance of the PN junction are measured, and the basic judgment is based on the values of them. Therefore, to do a good job in diode test, it is necessary to understand the basic structure and working principle of diodes, and then to understand the main fault characteristics of the diode. 1.3 Common Diode Failures Analysis1) open circuitThis means that the positive and negative electrodes of the diode have been disconnected, and the forward and reverse resistance of the diode have become infinite. After the diode is open, the circuit is in an open state.2) voltage breakdownThis means that there is a path between the positive and negative electrodes of the diode, and the forward and reverse resistance are as large as or close to each other(but not infinite). After a diode breaks down, the action between the positive and negative electrodes may always exit, because there are different manifestations in different circuits.3) forward voltageIf the forward resistance of the diode is too large, the voltage drop of the signal on the diode will increase, which will cause the output signal to decrease, and the diode will be damaged due to the heat. After the forward resistance becomes larger, the unidirectional conductivity of the diode will become poor.4) reverse voltageThe reverse resistance of the diode becomes smaller, which means the unidirectional conductivity of the diode be effected.5) performance degradationUnder this circumstance, the diode does not have obvious failures such as open circuit or breakdown. However, when the situation is getting worse, the stability of the circuit will deteriorate or the output signal voltage of the circuit will drop. Ⅱ How to Test Diode with a Multimeter?2.1 Digital Multimeter and Analog MultimeterWhen using a digital multimeter to test a diode, the red probe connects with the anode and the black probe connects with the cathode. At this time, the measured resistance is the forward conduction resistance of the diode, which is just the opposite of the test result of an analog multimeter. 2.2 Common Diodes Testing Rules(1) The forward resistance of the low-power germanium diode is 300Ω～500Ω, and the silicon diode is lkΩ or more. The former reverse resistance is tens of thousand ohms, and the latter is above 500kΩ (the value of high-power diode is smaller).(2) The polarity of the diode can be judged according to the resistance values (small forward resistance and large reverse resistance). Set the multimeter to the ohm block (Usually use R×100 or R×1k block, do not use R×1 block or R×10k block. The R×1 block is in a large current, it is easy to burn the tube, while using R×10k block may cause the tube broken down with high voltage). Connect the two polarities of the diode with the test probes respectively, and measure the two resistance values. When the measured resistance value is smaller, the end connected to the black lead is the anode. In the same way, when the measured resistance value is larger, the end connected to the black probe is the cathode. If the measured reverse resistance is small, it means that the diode is short-circuited, on the contrary, if the forward resistance is large, it means that the tube is open. In both cases, the diode can’t be work normally.(3) Silicon diodes generally have a forward voltage drop of 0.6V～0.7V, and the forward voltage drop of a germanium diode is 0.IV～0.3V. By measuring the forward voltage of the diode, it can be judged that the tested diode is a silicon tube or a germanium tube. This method is to connect a resistor (lkΩ) behind the power supply, and then connect with the diode according to the polarity characteristic to make the diode forward conducting. At this time, use a multimeter to measure the tube voltage drop. In addition, it is more convenient if it is used in energized dynamic measurement. 2.3 Testing Methods of Types of DiodesZener DiodesHow to test a Zener diode? The following here is to give some ideas.(1) Generally use the low-resistance block to test the Zener diode with a multimeter. Since the battery in the meter is 1.5V, this voltage is not enough to make the Zener diode reverse breakdown. So the forward and reverse resistance should be the same as a normal diode.(2) Measurement of the voltage stabilization value Vz of the Zener diode. When measuring diode, the power supply voltage must be greater than the stable voltage of the tube under test. In this way, the high-resistance block of the multimeter (R×10k) must be used. At this time, the battery in the meter has a higher voltage. When the multimeter's range is set to high barrier, measure diode reverse resistance. If the measured resistance is Rx, the voltage regulation value of the Zener diode is:In the formula, n is the override of the gear used. For example, if the highest electrical barrier ofR0 is the central resistance of the multimeter.E0 is the highest battery voltage value of the multimeter used.Example: Use an MF50 multimeter to measure a 2CW14 diode.R0=10Ω, the highest electrical barrier is R×10k.E0=15V, the measured reverse resistance is 75kΩ, then its voltage regulation value is:If the measured resistance is very large (close to infinite), it means that the voltage Vz under test is greater than E0, therefore, tube will not break down. If the measured resistance is very small (0 or only a few ohms), it means that the test probes are connected reversely, and then just swap the test probes. Light-emitting Diodes (LED)A light-emitting diode is a semiconductor device that converts electrical energy into light energy. It has the characteristics of small size, low working voltage and low working current.(1) There is a PN junction inside the light-emitting diode, so LED has the same characteristic of unidirectional conductivity. Its detection is similar to the measurement of ordinary diodes.(2) Use the R×1k or R×10k gear, and the forward and reverse resistance values are measured. Generally, the forward resistance is less than 50kΩ, and the reverse resistance is greater than 200kΩ.(3) The working current of the light-emitting diode is an important parameter. If the working current is too small, the light-emitting diode will not light up, and it is too large, the light-emitting diode will be easily damaged.(4) The forward turn-on voltage of the light-emitting diode is 1.2V ~ 2.5V, and the reverse breakdown voltage is about 5V. PhotodiodesPhotodiode is a semiconductor device that can convert light intensity into electrical signals.(1) There is a window on the top of the photodiode that can inject light, and the light irradiates the die through it. Under the excitation of the light, a large number of photoelectric particles are generated in the photodiode, which greatly enhances its conductivity and reduces internal resistance.(2) The photodiode is similar to the Zener diode. It also works in the reverse state, with reverse voltage.(3) The forward resistance of the photodiode does not change with the light. Its reverse resistance is larger when there is no light, and becomes smaller when it is exposed to light. That is, the stronger the light, the smaller the reverse resistance. Without light, the reverse resistance will return to the original value.(4) According to the related principle, use a multimeter to measure the reverse resistance of the photodiode. Change the light intensity when measuring, and observe the change of the reverse resistance of the photodiode. If there is no change or less change of the reverse resistance when light changes, it indicates that the tube has failed. High-speed Switching DiodesThe method of detecting high-speed silicon switching diodes is the same as that of ordinary diodes. The difference is that the forward resistance of this tube is relatively large. Measuring with Rxlk block, the forward resistance value is 5k ~ 10k in general, and the reverse resistance value is infinite. Fast Recovery Diodes / Ultrafast Recovery DiodesDetecting fast recovery and ultra-fast recovery diodes with a multimeter is basically the same as that of detecting plastic-encapsulated silicon rectifier diodes. That is, first use the Rxlk block to test its unidirectional conductivity. Generally, the size of forward resistance is about 4 ~ 5k, and the reverse resistance is infinite. And then use the Rxl block to repeat the test, at this time, the forward resistance is several ohms, and the reverse resistance is still infinite. DIAC (Diode for Alternating Current) DiodesUse the Rxlk block, and measure the forward and reverse resistance values of diac, which should be infinite. If the test probes are exchanged to measure, the pointer swings to the right, which indicates that the test tube has a leakage fault. Another method is placing the multimeter in the DC voltage block. During the test, shake the megohmmeter, and the voltage value indicated by the multimeter is the VBO value of the tube. Then change the two pins of the tested tube, and measure the VBR value in the same way. Finally, compare VBO and VBR. The smaller the difference between the absolute values of the two, the better the symmetry of the diac diode. TVS DiodesFor the dual TVS, resistance values between the two pins should be infinite when the red and black test probes of multimeter are exchanged at random. Otherwise, the tube has poor performance or has been damaged. High-frequency Varistor Diodesa. Identify Diode PolarityThe difference between high-frequency varistor diodes and ordinary diodes is that their color code is different. It is generally black of ordinary diodes, while high-frequency varistor diodes’ is light. Its polarity rule is similar to that of ordinary diodes. That is, the end with the green ring is the cathode, otherwise it is the anode.b. Measure Forward and Reverse ResistanceThe specific method is the same as the method of measuring ordinary diodes. Using the Rxlk block of a AM-500 multimeter, the forward resistance is 5k～55k, and the reverse resistance is infinite. Varactor DiodesUsing Rx10k block, no matter how the red and black test leads are exchanged for measurement, the resistance between the two pins of the varactor diode should be infinite. During the measurement, if the multimeter swings slightly to the right or the resistance value is zero, it means that the varactor diode under test has a leakage fault or has been broken down. No matter the loss of varactor diode capacity or internal open-circuit fault, it is impossible to detect them with a multimeter. When necessary, the replacement method can be used for inspection to make judgment. Infrared Light Emitting Diodes (IRED)Put the multimeter in the Rxlk block and measure the forward and reverse resistance of the IRED diode. Generally, the forward resistance should be about 30k, and the reverse resistance should be above 500k. It means the tube can work normally. The larger the reverse resistance, the better. IR Receiver Diodesa. Appearance Identification: Diode Cathode / Anode(1) Common infrared receiving diodes are black in appearance. In addition, there is a small oblique plane at the top of the tube body of the infrared receiving diode. Usually, the pin with one end of the oblique plane is the negative pole and the other end is the positive pole.(2) Use the Rxlk block to test the resistances between two pins. When a diode works normally, the resistance value of two pins are different. And exchange the test leads several times to get some pairs of values. According to the smaller resistance value, the pin connected to the red probe is the cathode, and the pin connected to the black probe is the anode.b. Performance DetectionUse a multimeter to measure the forward and reverse resistance of the infrared receiving diode. According to the resistance values, whether the diode is damaged can be judged preliminarily. Laser DiodesUse the Rxlk block of multimeter, and determine the order of the pins of the laser diode according to the method of detecting ordinary diodes. Because the forward voltage drop of the laser diode is larger than that of the ordinary diode, when detecting the forward resistance, the pointer of the multimeter is slightly deflected to the right, and the reverse resistance is infinite. Unijunction Transistor (UJT)a. Discrimination of ElectrodesBased on the R×1k block, use two meter pens to measure the forward and reverse resistance between any two of the three electrodes ( base B1 and base B2, and emitter E) of the ujt diode. The measured resistance values between the two electrodes are both 2~10kΩ, in addition, B1 and B2 will be different.b. Performance JudgmentThe performance of an ujt diode can be judged by measuring whether the resistance between its pins is normal. Use the R×1k barrier, the black test lead connect to the emitter E, and the red test lead connect to the two base electrodes in turn. Normally, a resistance value should be several thousand to ten thousand ohms. On the contrary, the red test lead connects to the emitter E, and the black test lead connects to the two base electrodes in turn, and the resistance should be infinite under normal conditions. The forward and reverse resistance values between the two bases are both in the range of 2~10kΩ. If they differ greatly from the normal value, the diode is damaged. Ⅲ Example Analysis3.1 Test a Diode in Circuita. Diode Test UsingAnalog MultimeterThe following measurements are all based on silicon diodes. If it is a germanium diode, the forward and reverse resistance of the diode will decrease.1) Measure forward resistance FRThe following figure is a wiring schematic diagram for measuring the forward resistance of a diode with an analog multimeter:Give the result as follows:IndicatorDescriptionUse the R×1k block to measure the diode, the forward resistance is several thousand ohms, and the pointer indicates stability. If the pointer swings slightly, it indicates that the thermal stability of the diode is poor.If the pointer indicates hundreds of kiloohms when measuring the forward resistance, it means that the diode is open.If the pointer indicates tens of kiloohms, it indicates that the diode has a large forward resistance and poor diode performance. Description of measurement of forward resistance:Forward Resistance (FR)DescriptionThousands of ohmsNormalZero or much less than a few thousand ohmsBreakdownHundreds of kilosLarge FR, the diode is openDozens of kilohmsLarge FR, bad forward characteristicsThe pointer is unstablePoor stability 2) Measure reverse resistance RRThe following figure is a wiring schematic diagram for measuring the reverse resistance of a diode with an analog multimeter:Give the result as follows:IndicatorDescriptionWhen measuring the reverse resistance, the value should be several hundred kiloohms. The larger the resistance value is, the better the indicator should be stable.If the reverse resistance is only a few thousand ohms, it means that the diode has broken down and has lost its unidirectional conductivity. Description of measurement of reverse resistanceReverse ResistanceDescriptionHundreds of kilosNormalZeroBreakdownMuch less than a few hundred thousand ohmsDiode’s reverse characteristic is not good.Pointer does not moveThe diode is open. Note: The reverse resistance of some diodes is very large, at this time, it is not certain that the diode is open, so that its forward resistance should be measured. If the value is normal, it means that the diode is not open.Pointer is unstableThe pointer cannot be stabilized at a certain resistance value during measurement, indicating that the diode has poor stability. 3.2 Power-off and Power-on Testing MethodsDiode in-circuit measurement is divided into two situations: Power-off and Power-on statea. Power-off MeasurementThere are something should be noted the method of this test.The influence of the external circuit on the test result is the same as the resistance and capacitance measured of internal circuit. And the influence of the measured forward resistance by the external circuit is lower than the reverse resistance.If there is any doubt about the measuring result, the diode should be removed from the circuit and measured separately. b. Power- on MeasurementWhen the circuit board is powered on, the test point is the tube voltage drop. Because the diode has a very important characteristic: when it is turned on, the tube voltage drop is basically unchanged. So the voltage drop is normal after being turned on, that is to say, the diode is normal.Measurement method: The diagram below shows the connection diagram of the tube voltage drop after the diode in the DC circuit. Setting multimeter in DC voltage 1 V block, the red probe is connected to the cathode of the diode, and the voltage indicated is the forward voltage drop of the diode. Diode forward voltage drop measurement results are analyzed as follows:DiodeDescriptionSilicon diode0.6VThe diode is normal and in a forward conducting state.> 0.6VThe diode is not in the conducting state.Close to 0The diode is in a breakdown state, the current in the loop will increase.Germanium diode0.2VThe diode is normal and in a forward conducting state.> 0.2VThe diode is off or is faulty.Close to 0In the breakdown state, the loop current increases significantly, without unidirectional conductivity. 3.3 ConclusionThe following points should be noted when measuring diodes:1) The diode in AC is in the cut-off state, because the diode is in the reverse state, and the reverse voltage at both ends is very large. The average voltage across the diode measured by the DC block is negative at this time.2) Use different blocks of the same multimeter to measure positive and negative resistance of one diode, their values will different. The forward and reverse resistances of the same diode measured with different multimeters are also different.3) When measuring the forward resistance of a diode, if the pointer cannot stop at a certain resistance value and constantly swings, it indicates that the thermal stability of the diode is not good.4) Some multimeters will provide a “diode check” function that displays the actual forward voltage of the diode when its conducting current. Such meters typically indicate a slightly lower forward voltage than what is “nominal state” for a diode, due to the very small amount of current used during the measurement. Frequently Asked Questions about Diode Test1. What is a diode test?A diode is best tested by measuring the voltage drop across the diode when it is forward-biased. ... A multimeter's Diode Test mode produces a small voltage between test leads. The multimeter then displays the voltage drop when the test leads are connected across a diode when forward-biased. 2. How do you test a rectifier diode?Touch the red (positive) probe of the multimeter to the positive terminal of the diode closet to the welder case interior. Touch the black (negative) probe of the multimeter to the negative terminal of the same diode. The multimeter should read a resistance between 0 and 1 ohm, or the diode is faulty. 3. How can you tell if a diode is positive or negative?Sometimes it's easiest to just use a multimeter to test for polarity. Turn the multimeter to the diode setting (usually indicated by a diode symbol), and touch each probe to one of the LED terminals. If the LED lights up, the positive probe is touching the anode, and the negative probe is touching the cathode. 4. How do you test a Schottky diode?Connect the red positive test lead to the anode of the Schottky diode and the black common test lead to the cathode of the diode. Listen for a “beep” or a “buzz” from the multimeter. If the Schottky diode responds as expected, the multimeter will sound a tone. 5. Can I test a diode in circuit?A diode is best tested by measuring the voltage drop across the diode when it is forward-biased. A forward-biased diode acts as a closed switch, permitting current to flow. A multimeter's Diode Test mode produces a small voltage between test leads. ... Voltage may be present in the circuit due to charged capacitors. 6. How do you check a diode?Diode PolarityThe polarity of both diodes is indicated with a stripe on one end of the body. The stripe corresponds to the line in the schematic symbol, indicating the cathode. The other end (no stripe) is the anode, indicated by the triangle in the schematic symbol. 7. What happens when a diode fails?However, a failed diode can short out too. In this case, the diode will exhibit a small resistance in both directions. The common reasons for a diode failure are excessive forward current and a large reverse voltage. Usually, large reverse voltage leads to a shorted diode while overcurrent makes it fail open. 8. How can you tell if a diode is blown?Turn the dial to “diode test” mode.This level of current is high enough to produce a reading, yet not so high that the diode will fail. It may also be labeled as “diode check” on your multimeter and is usually indicated by a small diode symbol. The diode symbol will look like a triangle pointing towards a line.

Ⅰ Introduction1.1 Diode Structure and SymbolThis Video Clearly Explains the  P-N Junction Semiconductor DiodeBasic diode consist of a tube, a case and two electrodes. The tube is a PN junction, and a pin is drawn at each end of the PN junction. Use plastic, glass, or metal material to make a package shell, as shown in the following figure. The electrode drawn out of the P area is called a positive electrode or anode, and the electrode drawn out of the N area is called a negative electrode or cathode.Figure 1. Simple Diode Structure and SymbolCatalogⅠ Introduction  1.1 Diode Structure and Symbol  1.2 Classification StandardⅡ Common Diodes DescriptionⅢ Diodes Comparison  3.1 Schottky Diode vs Common Diode  3.2 Transient Voltage Suppressor vs ESD Protection Diode  3.3 Light Emitting Diode vs Laser DiodeⅣ Diode Application  4.1 Rectification  4.2 Switch  4.3 Amplitude Limit  4.4 Freewheeling Role  4.5 DisplayⅤ Question Related to Diode types and Going Further  5.1 Question  5.2 Answer1.2 Classification Standard1) According to the material, it can be divided into germanium diode (Ge tube) and silicon diode (Si tube).2) According to the structure, it can be divided into point-contact diodes, surface-contact diodes and planar diodes. The point-contact diode has a small PN junction and cannot pass through a large forward current and withstand a high reverse voltage. However, it has good performance in high-frequency and is suitable for high-frequency detection circuits and switching circuits. The surface-contact diode has a large PN junction, can pass a large current and withstand a high reverse voltage, and is suitable for use in a rectifier circuit. When the planar diode is used as a switching tube in a pulse digital circuit, the PN junction contact is small, but the PN junction area is large when used for high-power rectification. There are two types of SMD diodes, leaded and leadless, and their common shapes are cylindrical and rectangular.3) According to use: include rectifier diode, detection diode, zener diode, varactor diode, photodiode, light emitting diode, switching diode, fast recovery diode, etc.Ⅱ Common Diodes DescriptionRectifier DiodesRectifier diodes can rectify AC power into pulsating DC power using the unidirectional conductivity characteristics. Because the forward current of the rectifier diode is relatively large, the structure always adopt to the surface-contact type. But this structure will cause a large junction capacitance. Generally, the operating frequency of the rectifier diode is less than 3KHz. Fully sealed metal structure packaging and plastic packaging are common for rectifier diodes. The rectifiers with a forward rated current of more than 1A are packaged in a metal shell to dissipate heat fully; the rectifiers with a forward rated current of less than 1A are mostly packaged with full plastic.Figure 2. RectifierWhen selecting a rectifier diode, the parameters such as its maximum rectified current, maximum reverse operating current, cut-off frequency and reverse recovery time are mainly considered. The rectifier tube used in the common series stabilized power supply circuit, its reverse recovery time of the cut-off frequency is not strict, therefore, only the maximum rectification current and the maximum reverse working current that meets circuit requirements can be selected. In addition, the rectifier circuit of the switching power supply and the pulse rectifier circuit should use rectifiers with high operating frequency and short reverse recovery time. Detection DiodesThe detection diode is a device that filters out the low-frequency signal superimposed on the high-frequency carrier. It has high detection efficiency and good frequency characteristics, and mostly uses a glass packaging structure. The detection diode has the characteristics of small forward voltage drop, high detection efficiency, small junction capacitance, and good frequency characteristics. When selecting a detection diode, high operating frequency, small reverse current, and sufficiently large forward current should be considered according to the circuit design requirements. Switching DiodesThe forward bias on-resistance of the switching diode is very low under, and the off-resistance is very large when the reverse bias is applied. Using the unidirectional conduction characteristics of the diode, the current can be turned on and off, so the tube is called a switching diode.Figure 3. Switching DiodeMedium-speed switch circuit and detector circuit can use 2AK series ordinary switch diode. High-speed switching circuit can choose RLS series, 1S series, 1N series, 2CK series high-speed switching diodes. The specific model of the switching diode should be selected according to the main parameters of circuits, such as forward current, maximum reverse voltage, reverse recovery time, etc. For example, the reverse recovery time (trr) refers to a time from the on-state to the fully off-state. Generally, the electron cannot be stopped immediately after being turned off, and a certain amount of reverse current flows, and the greater the leakage current, the greater the loss. The key characteristic of the switching diode is the fast on/off speed, which can meet the needs of high-frequency and ultra-high-frequency circuits. So it is often used in pulse digital circuits and automatic control circuits.Figure 4. Reverse Recovery Time (trr)Zener DiodesZener diodes achieve the purpose of voltage regulation according to the characteristic that the voltage basically does not change with the change of current when the PN junction reverses breakdown. It is divided according to the breakdown voltage, and its voltage regulation value is the breakdown voltage value. As a voltage regulator or voltage reference component, zener diodes can be connected in series to obtain a higher voltage regulation value. When selecting, the zener diode should comply with the circuit parameter requirements. For example, the stable voltage value of the zener diode should be the same as the reference voltage of the application circuit, and the maximum stable current should be higher around 50% than the maximum load current of the application circuit.Recommended Reading: Zener Diodes Tutorial: What is the Principle of Zener Diode? Avalanche DiodesThe avalanche diode is a microwave power device drew up on the basis of the voltage regulator technology. It can produce high-frequency oscillation under the effect of an external voltage. Avalanche diodes use avalanche breakdown to inject carriers into the crystal. Because the carrier takes a certain amount of time to travel across the semiconductor wafer, its current lags the voltage for a while. If the transit time is properly controlled, there will be a negative resistance effect on the current-voltage relationship, resulting in high-frequency oscillations. As for application, It is often used in microwave communications, radar, tactical missiles, remote control, telemetering, and other equipment. Fast Recovery DiodesThe fast recovery diode is a new type of semiconductor diode, which has sound switching characteristics and short reverse recovery time, and is usually used as a rectifier diode in high-frequency switching power supplies.The reverse recovery time is an important parameter for fast recovery diode. The definition of it is the time required for the diode to change from the forward on state to the cut-off state quickly, from zero output pulse to the reverse power supply to recover to 10% of the maximum reverse current.Super fast recovery diodes (SRD) are developed on the basis of fast recovery diodes, and their principal difference is that the shorter reverse recovery time. The reverse recovery time of an ordinary fast recovery diode is several hundred nanoseconds, and is generally several tens of nanoseconds for a SRD. The smaller the value, the higher the working frequency of diodes. When the operating frequency is in the range of tens to hundreds of kHz, the time for voltage changes of the ordinary rectifier diode is slower than the recovery time, and diodes cannot work normally based on unidirectional conduction. In this case, a fast recovery rectifier diode is required. Therefore, rectifier diodes used in switching power supplies for color TVs and other household appliances. Otherwise, electrical appliances may not work properly with ordinary rectifier diodes. Step Recovary Diodes Its structural characteristics are: a steep impurity distribution area at the boundary of the PN junction, thereby forming a "self-help electric field". Because the PN junction is under forward bias, it conducts with a small number of carriers, and has a charge storage effect near the PN junction, so that its reverse current needs a "storage time" before it can fall to the minimum (reverse saturation current value). The self-help electric field shortens the storage time, cuts off the reverse current quickly, and generates rich harmonic components. Utilizing these harmonic components, a special spectrum generating circuit can be designed, which mainly used in pulse and higher harmonic circuits. Schottky DiodesSchottky diode is a low-power, high-current, ultra-high-speed semiconductor device, its reverse recovery time is extremely short (can be as small as a few nanoseconds), the forward voltage drop is only about 0.4 V, but the rectified current can reach thousands of amps. These excellent characteristics are unmatched by fast recovery diodes.Figure 5. V-A CurveSchottky diode is a metal-semiconductor device made of precious metal (gold, silver, aluminum, platinum, etc.) as the positive electrode, and N-type semiconductor as the negative electrode, and the barrier formed on the contact surface of the two has rectifying characteristics. Schottky diodes are usually used in high-frequency, high-current, low-voltage rectifier circuits. In addition, some switching power supplies require it.Recommended Reading: Schottky Diode Characteristics and Its Applications Transient Voltage Suppressor (TVS)Transient voltage suppressor(TVS) is a commonly used circuit protection device, and has fast response time (sub-nanosecond level) and a fairly high surge absorption capacity. As its two ends are subjected to an instantaneous high-energy impact, the TVS can change the impedance value between the two ends from a high impedance to a low impedance at a very high speed to absorb an instantaneous large current and clamp the voltage on a predetermined value, to protect the subsequent circuit components from transient high voltage spikes. Its response to overvoltage is faster than the varistor or gas discharge tube. It is widely used in computers, electronic instruments, communication equipment, household appliances, and airborne/marine and automotive electronic equipment, also it can be used as a protective element such as overvoltage shock or lightning strikes.TVS can be divided into four categories according to their peak pulse power: 50W, 1000W, 1500W, and 5000W. It will turn on instantaneously when the voltage at both ends is higher than the rated value, and the resistance at both ends will change from high resistance to low resistance at a very high speed, absorbing a huge current and clamping the voltage at a predetermined value across the tube.Recommended Reading: Transient Voltage Suppressor Tutorial and Applications Light Emitting Diodes (LED)The light-emitting diodes are made of semiconductor materials such as gallium phosphide and gallium arsenide phosphide. In addition to the unidirectional conductivity characteristic of ordinary diodes, they can directly convert electrical energy into light energy. When a forward voltage is applied to the light-emitting diode, it is also in a conducting state. A forward current flows through the tube, it will emit light.The light-emitting color of the light-emitting diode is mainly determined by the material of the tube and the type of impurities incorporated. At present, the common light-emitting diodes have blue, green, yellow, red, orange, white and so on. The working current of the LED is usually 2～25mA. The operating voltage varies with different materials: ordinary green, yellow, red, and orange light-emitting diodes are about 2v; the operating voltage of white light-emitting diodes is usually higher than 2.4V, and the operating voltage of blue light-emitting diodes is usually higher than 3.3V. The working current of the LED cannot exceed the rated value, otherwise, there is a risk of burning. Therefore, a current limiting resistor is usually connected in series in the LED circuit. Infrared light-emitting diode is a special light-emitting diode, its shape is similar to LED, but it emits infrared light, which is invisible to human eyes under normal circumstances. Their working voltage is about 1.4V, and the working current is generally less than 20mA. In addition to single-color LEDs, there are two-color and three-color LEDs that can emit more than two colors of light.The PN junction of the light-emitting diode is packaged in a transparent plastic shell, and the shape is square, rectangular and round. Light-emitting diodes have the advantages of low driving voltage, small working current, strong anti-vibration and impact capabilities, small size, high reliability, power saving and long life, thus they are commonly used in circuits such as signal indication.Recommended Reading: Light-emitting Diode Basics Tutorial     LED Driver Basics and Its Circuit Design Laser DiodesLaser diodes are a type of diode similar to LEDs. They have similar characteristics to diodes, but in forward bias mode, they emit light and the voltage drop across ends acts as a load. The laser diode has the advantages of high efficiency, small size and long life, but its output power is small (generally less than 2mW). Their linearity is poor, also monochromaticity is not very good, so its application in the cable TV system is greatly restricted and cannot transmit multichannel and high-performance analog signals.There are two common laser diodes:①PIN photodiodeWhen it receives power to generate photocurrent, it will bring quantum noise.② Avalanche photodiodeIt can provide internal signal amplification, and the transmission distance is longer than the PIN photodiode, but its quantum noise is greater. PhotodiodesThe shell of a photodiode is equipped with a glass window to facilitate receiving light. Its characteristic is that when light is irradiated to its PN junction, free electrons and holes can be generated in pairs, so that the concentration of minority carriers in the semiconductor is increased. Under a certain reverse bias voltage, the reverse current increases. Therefore, its reverse current increases linearly with increasing light intensity. When there is no light, the volt-ampere characteristics of the photodiode are the same as ordinary diodes. As a light control element, the photodiode can be used for various object detection, photoelectric control, automatic alarm, etc. When a large photodiode is made, it can be used as an energy source called a photovoltaic cell. At this time, it does not need an external power supply, and can directly convert light energy into electrical energy.Recommended Reading: Avalanche Photo Diode Diode for Alternating Current (DIAC)The DIAC is a diode that conducts electrical current only after its breakover voltage has been reached momentarily. It is a silicon bidirectional voltage trigger switching device. When the voltage applied across the diode exceeds its breakdown voltage, the two ends are turned on, and the conduction will not stop until the current is interrupted or it drops to the minimum of the holding current of the device. DISC is usually used in overvoltage protection circuits, phase shift circuits, thyristor trigger circuits, and timing circuits. Varicap or Varactor DiodesVaractor diodes are special semiconductor devices that use reverse bias to change the capacitance of a PN junction. It is equivalent to a variable-capacity capacitor. The capacitance of the PN junction between its two electrodes changes with the magnitude of the reverse voltage applied to the two ends. As the voltage increases, the capacity of the varactor diode decreases. Owing to this characteristic, it is mainly used in electric tuning circuits (such as the LNB of color TV sets), as an automatic fine-tuning capacitor controlled by voltage.When choosing a varactor diode, it should be focused on operating frequency, maximum reverse operating voltage, maximum forward current, and zero bias junction capacitancc in the circuit. The varactor diode with low revere leakage current and various junction capacitance should be selected. Freewheeling DiodesGenerally, a fast recovery diode or a Schottky diode is selected as a "freewheeling diode". It is generally used in the circuit to protect the component from breakdown by induced voltage or burned out. Connect in parallel to the two ends of the element that generates the induced electromotive force(EMF), and forms a loop with it, so that the high EMF generated in the loop is consumed by the current, thereby protecting the components in the circuit.Freewheeling diodes are often used with energy storage elements to prevent sudden changes in voltage and current, and provide a path. The inductor can provide a continuous current to the load through it, so as to prevent the load current from abruptly changing and play a role in smoothing  current. In the switching power supply, a freewheeling circuit composed of diodes and resistors connected in series. The freewheeling diode of this circuit is connected in parallel with the transformer. When the switching tube is turned off, the freewheeling circuit can release the energy stored in the transformer coil to prevent the induced voltage from being too high to damage the switch tube. In fact, freewheeling diode is not a substantial component, it is just having freewheeling function in the circuit.Recommended Reading: What Is A Flyback Diode or Freewheeling Diode and It's Applications Gunn DiodeGunn diode, also called transferred electron device (TED), is a form of diode used in high-frequency electronics. Unlike ordinary diodes that have both a N-type region and a P-type region, it consists of N-type impurity semiconductor only.The Gunn diode has three regions: the two ends are N-type impurity doped regions, and there is a lightly doped thin layer between them. When a voltage is applied across the Gunn diode, electrical gradients at the central thin layer are the largest. Because in the conductor material, the current is proportional to the voltage, conductivity will be generated. Eventually, a higher electric field value will be generated at the central thin layer, resulting in a higher resistance to prevent further increase in conductivity, thus the current will start to decrease. This means that the Gunn diode has a negative resistance effect, or called negative differential resistance. It is commonly used to generate microwave signals and has been used as a simple and effective form of microwave generator in many RF circuit designs. Tunnel DiodesIt is a crystal diode with a tunneling current as the main current, and is a two-terminal active device. The base materials are gallium arsenide and germanium. The N-type region and the P-type region is highly doped (ie, with a high concentration of impurities). The tunneling current is produced by the quantum mechanical effect of semiconductors, which has the following three conditions: the conduction band and the full band are Fermi level; the width of the space charge layer must be narrow (below 0.01 microns); the holes in the P-type and N-type regions of will overlap with electrons at the same energy level. Tunnel diodes can be used in high-frequency amplifiers with low noise and high-frequency oscillators (whose operating frequency can reach the millimeter), and can also be used in high-speed switching circuits. PIN DiodesThis is a crystal diode with a layer of intrinsic semiconductor (or semiconductor with low concentration of impurities) between the P region and the N region. When its operating frequency exceeds 100MHz, due to the storage effect of minority carriers and the transit time effect in the intrinsic layer, diode loses rectifying function and becomes an impedance element, and its impedance value varies with the bias voltage. Therefore, the PIN diode can be used as a variable impedance element. It is often used in high-frequency switches such as microwave switches, phase-shifting, modulation, amplitude limit and other circuits. Damper Diodes Damper diode has a lower voltage drop and a higher operating frequency, can withstand a higher reverse operating voltage and peak current, and has a small forward voltage drop. It is similar to a high-frequency high-voltage rectifier diode, and used for damper and booster rectification. Vacuum DiodesVacuum diode, also called electron diode or valve, or vacuum tube. A tube with only one cathode and one anode. It is conducted by the electron emitted by the cathode based on heated filament. Because the filament has heat loss, the performance is poor than that of the semiconductor diode.When the anode potential is higher than the cathode, the electrons emitted by the cathode move to the anode to form an electron flow under the action of the electric field. When the cathode voltage is higher than the anode, the electric field force received by the electrons pulls the electrons back to the cathode, and cannot generate current. That is unidirectional conductivity. It is generally used for rectification and detection. There are two types of vacuum tube, vacuum and gas (filled with an inert gas). The latter can also be used for voltage stabilization, indication and system control.Recommended Reading: What is Vacuum Tube? Basic Structure and TypesFull Diode Symbols Display Ⅲ Diodes Comparison3.1 Schottky Diode vs Common DiodeFor common diode, the initial conduction voltage drop of the silicon tube is about 0.5V, the normal conduction voltage drop is about 0.7V, the conduction voltage drop is about 1V when it is close to the limit current. The initial conduction voltage drop of the germanium tube is about 0.2V, the normal turn-on voltage drop is about 0.3V, and the turn-on voltage drop is about 0.4V when it is close to the limit current. For Schottky diode, the initial turn-on voltage drop is about 0.4V, the normal turn-on voltage drop is about 0.5V, and the turn-on voltage drop is about 0.8V when it is approaching limit current.Both diodes are unidirectional and can be used in rectification applications. The difference is that the withstand voltage of common silicon diodes can be higher, but its recovery time is long, and it can only be used for low-frequency rectification. If it is used in high frequency, reverse leakage will occur to cause tube burned. Withstand voltage of Schottky diode is low, but its recovery time is short and can be used in high frequency occasions. 3.2 Transient Voltage Suppressor vs ESD Protection DiodeTVS is mainly for transient voltage suppression, and ESD is mainly used for electrostatic discharge protection. As for anti-static, it requires low capacitance value, generally between 1 ~ 3.5PF is the best, ESD meets the requirements well. However, TVS cannot do this, because the capacitance of TVS is relatively high. 3.3 Light Emitting Diode vs Laser DiodeLED uses the spontaneous emission of carriers injected into the active area to emit light, while LD emits light from laser radiation. The direction of the light emitted by the LED is random, and the LD light is in the same direction and phase. The LD has an optical resonant cavity, so that the generated photons oscillate and amplify in the cavity, and the LED has no that. The LED has no critical value, the spectral density is several orders of magnitude higher than that of the LD, the LED light output power is small, and the divergence angle is large. LEDs are commonly used in the indicator light of electrical equipment such as traffic lights. They have the characteristics of long service life and high photoelectric conversion efficiency. While LD is widely used in low-power photoelectric devices such as CD drives on computers and print part of laser printers.Ⅳ Diode Application4.1 RectificationAccording to the unidirectional conductivity, a diode can transform the alternating current into a pulsed direct current with a single direction.4.2 SwitchUnder the action of forward voltage, the resistance of the diode is very small, it is in the on state, which is equivalent to a switch on; under the action of the reverse voltage, the resistance is large, and it is in the off state, just like a switch off. Using the switching characteristics of the diode, various logic circuits can be made.4.3 Amplitude LimitAfter the diode is forward-conducted, its forward voltage drop remains basically the same (0.7V for silicon tube and 0.3V for germanium tube). Using this feature, diode often regarded as a limiting element in the circuit to limit the signal amplitude to a certain range.4.4 Freewheeling RoleIt plays a freewheeling role in the inductance of the switching power supply and inductive loads such as in relays.4.5 DisplayDiodes are commonly used in VCD, DVD, traffic lights and other displays. Ⅴ Question Related to Diode types and Going Further5.1 QuestionHow are diodes classified? 5.2 AnswerDiodes are classified according to their characteristics and are offered in a number of different types based on circuit requirements, including rectifier diodes, switching diodes, light emitting diodes, Schottky diodes, Zener diodes, and diodes designed for high-frequency applications, etc. Frequently Asked Questions about Different Types of Diode1. What are the different types of diode?Different Types of DiodesSmall Signal DiodeLarge Signal DiodeZener DiodeLight Emitting Diode (LED)Constant Current DiodesSchottky DiodeShockley DiodeStep Recovery Diodes 2. What is diode and its types?A diode is a two-terminal electrical device, that allows the transfer of current in only one direction. ... Most of the diodes are made from semiconductors such as Si (silicon), but in a few cases, Ge (germanium) is also used. It is sometimes beneficial to summarize the different types of diodes are existing. 3. How do you identify a Schottky diode?The Schottky diode is measured in both forward And reverse directions. If the re a, the measurement in Figure 8-25 indicates that the tube is a silicon diode. If it is a germanium diode, the forward voltage reading should be less than 0.3V. 4. What is the application of a diode?The application areas of diodes include communication systems as limiters, clippers, gates; computer systems as logic gates, clampers; power supply systems as rectifiers and inverters; television systems as phase detectors, limiters, clampers; radar circuits as gain control circuits, parameter amplifiers, etc.

I IntroductionThe light-emitting diode is a commonly used light-emitting device, which emits energy through the recombination of electrons and holes. It is widely used in the field of lighting. Light-emitting diodes can efficiently convert electrical energy into light energy. Light-emitting diodes have a wide range of uses in modern society, such as lighting, flat panel displays, and medical devices.Light Emitting Diode (LED) Working PrincipleThis kind of electronic component appeared as early as 1962. In the early days, it could only emit low brightness red light. Later, other versions of monochromatic light were developed. The light that can be emitted today has spread to visible light, infrared light, and ultraviolet light. Initially,  the light-emitting diodes were used as indicator lights, display panels, etc. With the continuous progress of technology, light-emitting diodes have been widely used in displays and lighting.CatalogI IntroductionII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters2.2 Significance of Electrical ParametersIII Working Principle of Light-emitting DiodeIV Types of Light-emitting DiodeV Materials of a Light-emitting Diode5.1 Wafer5.2 Bracket5.3 Silver glue 5.4 Gold wire 5.5 Epoxy resinVI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal Display6.2 Automotive Industry6.3 LCD Backlight6.4 LED Lighting6.5 Other ApplicationsVII Trends of LED Lighting TechnologyII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters(1) Allowable power consumption Pm: the maximum value of the product of the forward DC voltage applied to both ends of the LED and the current flowing through it. If this value is exceeded, the LED becomes hot and damaged.(2) Maximum forward DC current IFm: the maximum forward DC current allowed to be added. Exceeding this value can damage the diode.(3) Maximum reverse voltage VRm: the maximum reverse voltage allowed to be applied. Above this value, the light-emitting diode may be damaged by the breakdown.(4) Working environment topm: the ambient temperature range where the LED can work normally. Below or above this temperature range, the light-emitting diode will not work properly and the efficiency is greatly reduced.2.2 Significance of Electrical Parameters(1) Spectral distribution and peak wavelength: the light emitted by a certain light-emitting diode is not a single wavelength, and its wavelength is generally shown in Figure.Figure 1. Spectral Distribution and Peak WavelengthIt can be seen from the figure that the light intensity of a certain wavelength λ0 in the light emitted by the light-emitting tube is the largest, and this wavelength is the peak wavelength.(2) Luminous intensity IV: The luminous intensity of the light-emitting diode usually refers to the luminous intensity in the direction of the normal. When the radiation intensity in this direction is (1/683) W / sr, it emits 1 candela (symbol cd). Since the general LED has a low luminous intensity, the luminous intensity is usually measured in candela (mcd).(3) Spectral half-width Δλ: It represents the spectral purity of the light-emitting tube. It refers to the interval between the two wavelengths corresponding to the 1/2 peak light intensity in Figure 3.(4) Half value angle θ1 / 2 and viewing angle: θ1 / 2 refers to the angle between the direction in which the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction).Two times the half-value angle is the viewing angle (or half-power angle).Figure 2. Angle Distribution of Luminous Intensity of the LEDFigure above shows the angular distribution of the luminous intensity of two different types of LEDs. The coordinates of the perpendicular (normal) AO are the relative luminous intensity (ie, the ratio of the luminous intensity to the maximum luminous intensity). Obviously, the relative luminous intensity in the normal direction is 1. The larger the angle away from the normal direction, the smaller the relative luminous intensity. From this graph, the half-value angle or viewing angle value can be obtained.(5) Forward working current If: It refers to the forward current value when the light-emitting diode is normally emitting light. In actual use, the IF should be selected below 0.6·IFm.(6) Forward working voltage VF: The working voltage given in the parameter table is obtained under a given forward current. Generally measured at IF = 20mA. The forward working voltage VF of the light-emitting diode is 1.4 ~ 3V. When the outside temperature increases, VF will decrease.(7) V-I characteristics: The relationship between the voltage and current of the light-emitting diode can be represented in the figure below.Figure 3. The Relationship between the Voltage and Current of the LEDWhen the forward voltage is less than a certain value (called a threshold), the current is extremely small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and emits light. From the V-I curve, parameters such as the forward voltage, reverse current, and reverse voltage of the light-emitting tube can be obtained. The forward leakage current IR of the LED tube is less than 10μA.III Working Principle of Light-emitting DiodeThe core part of the light-emitting diode is a wafer composed of a P-type semiconductor and an N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, called a PN junction. In the PN junction of some semiconductor materials, the injected minority carriers and majority carriers will release excess energy. The energy is in the form of light, thereby directly converting electrical energy into light energy. The reverse voltage is added to the PN junction. Minority carriers are difficult to inject, so they do not emit light. This kind of diode is called a light-emitting diode, commonly known as LED. When it is in the forward working state (that is, the forward voltage is applied to both ends), and when the current flows from the anode to the cathode of the LED, the semiconductor crystal emits light of different colors from ultraviolet to infrared. The intensity of the light is related to the current.The principle of light-emitting diode needs to be analyzed from the following three situations:When no voltage is applied across the diode, the electrons in the N-type material will move along the PN junction between the layers. The electrons fill the holes in the P-type material and form a depletion region. In the depletion region, the semiconductor material returns to its original insulation state. That is, all holes are filled, so there is neither free electrons nor space for electrons to move in the depletion region, and the charge cannot flow.Figure 4. No Voltage is Applied Across the DiodeWhen a forward voltage is applied to the light-emitting diode, the holes injected from the P region to the N region. And the electrons injected from the N region into the P region within a few microns near the PN junction. They recombine with electrons in the N region and holes in the P region respectively. Therefore, they produce spontaneously emitted fluorescence. Different semiconductor materials have different energy states for electrons and holes. The more energy released, the shorter the wavelength of the emitted light. Diodes that emit red, green, or yellow light are commonly used.Figure 5. Apply a Forward Voltage to the LEDWhen a reverse voltage is applied to the light-emitting diode, the P-type terminal is connected to the negative electrode of the circuit, and the N-type terminal is connected to the positive electrode. And the current will not flow. Negatively charged electrons in N-type materials will be attracted to the positive electrode. Positively charged holes in P-type materials will be attracted to the negative electrode. Since holes and electrons move in the wrong direction. No current will flow through the PN junction, and the depletion region will also expand.Figure 6. Apply a Reverse Voltage to the LED LED materialColorAlGaAs GaAsP AlGaInP GaP:ZnOred and infrared InGaN/GaN GaP AlGaInP AlGaPgreenGaAsPAlGaInP AlGaInP GaPhigh brightness orange red, orange, yellow, greenGaAsPred, orange, yellowGaP ZnSe InGaN SiCred, yellow, greenGaNgreen, emerald green, blueInGaNnear ultraviolet, blue green, blueSiCblueSiblueAl2O3blueZnSeblueCultravioletAlN AlGaNUV with wavelengths far to nearTable: Inorganic Semiconductor Materials Used in Light-emitting Diodes and the Colors They EmitIV Types of Light-emitting DiodeThere are various types of light-emitting diodes according to different aspects. According to the materials used, there are gallium phosphide (GaP) light-emitting diodes, phosphorous gallium arsenide (GaAsP) light-emitting diodes, gallium arsenide (GaAs) light-emitting diodes, phosphorous indium gallium arsenide (GaAsInP) light-emitting diodes and gallium arsenide aluminide (GaAlAs) light-emitting diodes.According to its packaging structure and packaging form, there are metal packaging, ceramic packaging, plastic packaging, resin packaging, and leadless surface packaging. It can also be divided into additive color scattering package (D), colorless scattering package (W), colored transparent packaging (C), and colorless transparent packaging (T).Figure 7. Kinds of Light-emitting DiodeAccording to its package shape, it can be divided into circular, square, rectangular, triangular, and combined shapes. The figure shows the shape of several light-emitting diodes.Plastic light-emitting diodes are divided into red, amber, yellow, orange, light blue, green, black, white, transparent, and colorless according to the color of the tube body. The outer diameter of the round light-emitting diode is from ￠ 2 to ￠ 20mm. According to the light-emitting color of the light-emitting diodes, it can also be colored light and infrared light. Colored lights include red light, yellow light, orange light, green light, and so on. In addition, light-emitting diodes can be divided into ordinary monochrome light-emitting diodes, high-brightness light-emitting diodes, ultra-high-brightness light-emitting diodes, color-changing light-emitting diodes, flashing light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes, and negative resistance light-emitting diodes.V Materials of a Light-emitting DiodeWafer, bracket, silver glue, gold wire, and epoxy resin are the five LED raw materials of light-emitting diode5.1 WaferThe structure of the wafer: it consists of a gold pad, P-pole, N-pole, PN junction, and a back gold layer (the double-pad wafer has no back gold layer). The wafer is composed of P-layer semiconductor elements and N-layer semiconductor elements. They are rearranged and combined by electron movement. It is this change that enables the wafer to be in a relatively stable state. When the positive electrode is applied to the wafer with a certain voltage, the holes in the positive P region will continue to swim toward the N region. And the electrons in the N region will move to the P region relative to the holes. While the electrons and holes move relatively, the electron holes pair with each other, exciting photons and generating light energy.The main classification of wafer: surface-emitting type: most of the light is emitted from the surface of the wafer. Five-sided light-emitting type: there is more light emitted on the surface and side.5.2 BracketThe structure of the bracket is 1 layer of iron, 1 layer of copper (good conductivity, fast heat dissipation), 1 layer of nickel (anti-oxidation), 1 layer of silver (good reflectivity, easy to solder wire)5.3 Silver glue Take H20E as an example. Silver glue is also called white glue, milky white. The role of silver glue is to conduct and bond materials (baking temperature: 100°C / 1.5H). Storage conditions: Silver glue manufacturers generally store silver glue at -40°C, and application units generally at -5°C. Single-agent is 25°C / 1 year (dry, ventilated place), mixed agent 25°C / 72 hours. Baking conditions: 150°C / 1.5H. Stirring conditions: Mix for 15 minutes in one direction.5.4 Gold wire Take φ1.0mil as an example. The gold wires used for LEDs are φ1.0mil and φ1.2mil. The material of the gold wire is generally 99.9% of the gold content of the gold wire for LED. The purpose of the gold wire: with its characteristics such as high gold content, soft, easy to deform, good conductivity and good heat dissipation, a closed circuit is formed between the wafer and the bracket. (Conversion relationship: 1 mil = 0.0254mm, 1 in = 25.4mm)5.5 Epoxy Resin Ttake EP400 as an example. Composition: A and B two parts: Glue A: it is the main agent, which consists of epoxy resin + defoamer + heat resistance agent + thinner. Agent B: it is a curing agent, consisting of acid, mold release agent, and accelerator.VI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal DisplayLED lamp has the characteristics of shock resistance, fast light response, power-saving, and long life, etc. It is widely used in various indoor and outdoor displays. It is divided into full-color, three-color, and monochrome displays that are developed and produced by more than 100 units nationwide. Traffic lights mainly use ultra-high-brightness red, green, and yellow LEDs. Because LED lights are energy-saving and reliable, the traffic lights are gradually being replaced throughout the country and the speed of promotion is fast.Figure 8. Traffic Lights6.2 Automotive IndustryAutomotive lamps include dashboards, audio indicators, backlights for switches, reading lights and external brake lights, tail lights, sidelights, and headlights. Incandescent lamps for automobiles are not resistant to shock that require frequent replacement. Due to the fast response speed of the LED, the driver can be reminded of the brakes early to reduce the rear-end accident. In developed countries, the central rear high-position brake light made of LED has become a standard part of the car. The LED car tail light model launched by the American HP company in 1996 Groups can be combined into various car taillights at will. In addition, the light sources in the car dashboard and other various lighting parts can be used as ultra-high brightness light-emitting lamps. In recent years, an annual output value of 1 billion yuan will be formed, and within 5 years, an annual output value of 3 billion yuan will be formed.Figure 9. Automotive Headlight6.3 LCD BacklightLED backlights are most noticeable with high-efficiency side-emitting backlights. As an LCD backlight application, LEDs have the characteristics of long life, high luminous efficiency, no interference, and high-cost performance. They have been widely used in electronic watches, mobile phones, BP, computers, electronic calculators, and credit card machines. With the increasing miniaturization of portable electronic products, the LED backlight has more advantages.  The backlights manufacturing technology will be developed to thinner, low power consumption, and uniformity. LED is the key device of a mobile phone. An ordinary mobile phone needs about 10 LED devices, while a color screen and a mobile phone with camera function need to use about 20 LED devices. At present, the amount of mobile phone backlight is very large. 3.5 billion LED chips are used a year.6.4 LED Lighting  Early lighting products have low luminous efficiency. The light intensity can only reach a few to dozens of mcd, which is suitable for indoor occasions, such as home appliances, instrumentation, communication equipment, microcomputers, and toys. At present, the direct goal is to replace incandescent lamps and fluorescent lamps with LED light sources. This substitution trend has started to develop from local application fields. To save energy, Japan is planning to replace the incandescent light-emitting diode project (called "illuminate Japan"). The budget for the first five years is 5 billion yen. If LED replaces half of the incandescent and fluorescent lamps, the annual savings can be equivalent to the energy of 6 billion liters of crude oil. That is equivalent to the power generation of five 1.35 × 106kW nuclear power plants. It can reduce the production of carbon dioxide and other greenhouse gases and improve the living environment.6.5 Other ApplicationsFigure 10. LED Christmas LightsOther applications such as a kind of flash shoes popular with children, the built-in LED will flash when walking; the power indicator of electric toothbrushes; the popular LED Christmas lights. Due to the novel shape, rich colors, unbreakable and low-voltage safety Sexuality, LED Christmas light is generally welcomed by people. It is threatening and replacing the existing Christmas market of electric bulbs.VII Trends of LED Lighting Technology1. The mainstream light source of lighting will be converted to LED. At present, the luminous efficiency of high-power led commercial products has reached more than 150lm / W. The life span has reached more than 30,000 hours. The comprehensive performance of LEDs has exceeded other light sources. At the same time, in addition to large power, the price of LED lamps is close to lamps composed of other light sources. Therefore, LED already has certain advantages. At the same time, the light efficiency of LED laboratory products has reached more than 300lm / W. Through a reasonable heat dissipation design, the life span of more than 50,000 hours can be fully achieved. In principle, there is not much room for other light sources to improve light efficiency and life. Therefore, it can be expected that LED becoming the mainstream light source in the lighting market.2. The research of LED device technology will mainly focus on the improvement of green LED efficiency. The core device of semiconductor technology-LED, currently the red LED and the blue LED has high photoelectric efficiency, but the photoelectric efficiency of the green LED is very low. This limits the substantial application of LED spectral flexibility. Therefore, improving the light efficiency of green LEDs is the most important research topic of LED devices.3. Another study of LED technology will be the study of narrow-spectrum LED devices. The narrow spectral width of a single LED will help to truly achieve unlimited flexibility in assembling the LED spectrum. At the same time, one of the main applications of LEDs at present-LED displays, if the spectral width of monochromatic LEDs can be reduced, a larger color gamut space can be achieved.4. White LEDs for general lighting will gradually shift to RGB mode. The light sources used for general lighting are presented in the form of white light or near-white light. At present, the most comprehensive and cost-effective white LEDs on the market are also implemented by blue LEDs and YAG phosphors. However, the RGB method has higher light efficiency. It will enable the lamp to be dimmed, toned, and even adjusted the color rendering index. Therefore, with the improvement of green LED light efficiency, it is believed that the RGB method (further extended to 3 or more monochromatic LED mixed colors) will become the mainstream white LED mode.5. The characterization of the color rendering of the light source will be a long-term debate. The characterization in the form of the spectrum may be the ultimate result. The current parameter that characterizes the color rendering of the light source is the color rendering index. However, this is based on the limited spectral form of traditional light sources. The infinite flexibility of the LED spectrum will make this characterization problematic. It can be predicted that if the LED achieves true spectrum unlimited flexibility. Any single-parameter color rendering will actually be flawed, and the ultimate characterization method should be the spectrum itself.6. The application of light sources will include two basic aspects of visual applications and non-visual applications. The flexibility of LEDs in spectral assembly makes it possible to achieve various visual and non-visual optimized applications through spectral assemblies, such as agricultural lighting, medical lighting, LED Visible light communication, etc. But relatively speaking,  in the non-visual field, there are still many problems to be solved, including what kind of lighting conditions are optimized, the price of LED needs to be further reduced. The former is a scientific problem, while the latter is an industrialization problem.7. Lighting technology will be deeply integrated with information technology to create smart lighting. As a semiconductor device, LED is a good physical carrier of information technology because LED is easy to control plus the relevance of lamps and human life. Therefore, LED can be deeply integrated with information technology, and smart lighting will be born. This will be an important development direction for future LED lighting technology.8. The appearance of the lamps and lanterns will have great innovation potential. At present, most LED lamps and lanterns include LED bulbs, LED downlights, LED tubes, etc., all of which are designed to cater to people's consumption habits. Whether this is the best mechanical form of the lamp or not remains to be studied. At least, there is a lot of room for innovation in the future mechanical form of LED lamps.9. OLED will occupy an important position in the display field. Relative to LEDs that emit light similar to point light sources, OLEDs emit light in the form of surface light sources. Therefore, after LED occupies the vast majority of lighting applications in the future, OLED still has certain advantages in the display field.10. Natural lighting will be valued. In recent years, energy-saving lighting, health lighting, and ecological lighting have received great attention. The use of sunlight to achieve lighting naturally becomes the best choice. Therefore, with the advancement of technology, natural light lighting will receive more and more attention.Due to the great flexibility of LEDs in the three dimensions of scale, spectrum, and time, many innovative applications and concepts may be born in the future of LED development. This is the development trend of lighting based on artificial light sources. At the same time, as people continue to deepen the concept of green environmental protection, natural lighting will also get greater development. Frequently Asked Questions about Light-emitting Diode Tutorial1. What does light emitting diode mean?In the simplest terms, a light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it. Light is produced when the particles that carry the current (known as electrons and holes) combine together within the semiconductor material. 2. What is a light emitting diode used for?Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do many different jobs in all kinds of devices. They form numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. 3. What type of light does LED emit?LED lighting differs from incandescent and fluorescent in several ways. When designed well, LED lighting is more efficient, versatile, and lasts longer. LEDs are “directional” light sources, which means they emit light in a specific direction, unlike incandescent and CFL, which emit light and heat in all directions. 4. Why are LED lights so bright?LED lights are so bright because they have a high lumen/watt score. ... This is an enormous difference between the levels of light you are getting from each bulb and because the LED bulb is so much higher there is no way that you would need to replace a 40W incandescent bulb with the equivalent Watt in a LED. 5. What is the difference between diode and LED?The most significant difference between the LED and diode is that the LED emits the light while the diode allows the current to flow only in one direction and opposes the flow in the opposite direction. 6. What is the basic principle of LED?Working Principle: A light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. 7. Do LED lights give off UVB?Some in the lighting business have stated that LEDs do not produce UV radiation. However studies have shown that standard LEDs do create a small amount of UV. That said, the amount of UV they actually emit is even less. This is due to the phosphors within an LED lamp that convert the Ultraviolet light to white light. 8. What are the two basic types of LEDs?The two basic types of LEDs are indicator-type LEDs and illuminator-type LEDs. Indicator-type LEDs are usually inexpensive, low-power LEDs suitable for use only as indicator lights in panel displays and electronic devices, or instrument illumination in cars and computers. 9. What is LED and its advantages?Safety is perhaps the most often overlooked advantage when it comes to LED lighting. The number one hazard when it comes to lighting is the emission of heat. LEDs emit almost no forward heat while traditional bulbs like incandescents convert more than 90% of the total energy used to power them directly into heat. 10. What is the O in OLED?Organic contrastOLED stands for organic light-emitting diode. Each pixel in an OLED display is made of a material that glows when you jab it with electricity.

Ⅰ Working Principle1.1 TerminologyA diode is a two-terminal electronic device characterized by unidirectional conductivity—it allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction. Historically, diodes are divided into vacuum tube diodes (formerly called electron diodes) and semiconductor diodes (crystalline diodes). Due to the high heat loss, large size, and lower efficiency of vacuum tubes, semiconductor diodes are the standard in modern electronics.The fundamental principle of a modern diode relies on the PN junction. Adding leads and a protective package to this PN junction creates the discrete component we know as a diode.A semiconductor diode consists of a PN junction formed by joining a P-type semiconductor and an N-type semiconductor. A depletion region (space charge layer) forms at the interface, creating a self-built electric field. In the absence of applied voltage, the diffusion current (caused by the difference in carrier concentration) and the drift current (caused by the internal electric field) balance each other out, resulting in a state of electrical equilibrium.Forward Bias: When a forward voltage is applied, the external electric field opposes the self-built field. This lowers the barrier, causing the diffusion current of carriers to increase significantly, resulting in a forward current (conduction).Reverse Bias: When a reverse voltage is applied, the external field reinforces the self-built field. This widens the depletion region and prevents majority carriers from crossing. Only a tiny "reverse saturation current" flows (leakage), which remains roughly constant over a specific voltage range.Breakdown: When the reverse voltage exceeds a critical threshold, the electric field strength in the depletion layer becomes high enough to trigger a multiplication of carriers. This generates a large number of electron-hole pairs, causing a sharp increase in reverse current. This is known as the breakdown phenomenon. It is worth noting that reverse breakdown is categorized into two types: Zener breakdown (in highly doped junctions at lower voltages) and Avalanche breakdown (at higher voltages). Figure 1. P-type Semiconductor and N-type Semiconductor 1.2 PN JunctionA PN junction is the boundary interface between two types of semiconductor materials: P-type and N-type. The "P" (Positive) region contains an excess of holes, while the "N" (Negative) region contains an excess of free electrons. Due to the concentration gradient, free electrons from the N region diffuse into the P region, and holes from the P region diffuse into the N region. This movement creates the depletion region at the junction.Metal leads are connected to these regions to form terminals: the lead connected to the P-region is the Anode (positive pole), and the lead connected to the N-region is the Cathode (negative pole).1.2.1 Doping PrincipleP-type formation: Intrinsic semiconductors (pure silicon) are doped with trivalent impurities (Group III elements), such as Boron. A Boron atom has only three valence electrons. When it forms covalent bonds with surrounding silicon atoms (which have four electrons), a "hole" (a lack of an electron) is created in the lattice. This hole can accept an electron, effectively making the Boron atom a static negative ion. In P-type material, holes are the majority carriers.N-type formation: Similarly, when intrinsic silicon is doped with pentavalent impurities (Group V elements), such as Phosphorus, the impurity atoms form covalent bonds with silicon. Since Phosphorus has five valence electrons, one excess electron is left free to move. In N-type material, free electrons are the majority carriers. Figure 2. PN Junction StructureWhen these two regions meet, the diffusion of electrons and holes across the boundary disrupts the electrical neutrality near the junction, creating an electric field that eventually stops further diffusion, establishing equilibrium.1.2.2 Feature: Unidirectional ConductivityWhen forward voltage is applied (Anode positive, Cathode negative), the external field pushes holes and electrons toward the junction. This narrows the depletion region and neutralizes the internal electric field. Once the voltage exceeds the threshold voltage (typically ~0.7V for Silicon, ~0.3V for Germanium), the diode conducts current with very low resistance.1.2.3 Supplementary NoteForward Bias: Current flows easily; the diode acts like a closed switch (low impedance).Reverse Bias: Current is blocked; the diode acts like an open switch (high impedance). Ⅱ Diode ApplicationsDiodes are ubiquitous in electronics. From simple power conversion to complex signal processing, they protect circuits, regulate voltage, and enable logic functions. Understanding the diode is the first step to mastering electronics.Function of a Diode in Circuit Design2.1 Main FunctionsDiodes serve four primary roles in modern circuitry:(1) Switching Circuit (Current Steering)In digital logic and computing, diodes utilize their unidirectional conductivity to act as automatic switches. They ensure current flows only when specific conditions are met (like in AND/OR logic gates). Switching diodes (like the 1N4148) are optimized for speed, offering much faster response times than mechanical switches and preventing damage from reverse currents.(2) Limiter/Clipper Circuit (Signal Control)Limiter circuits (or clippers) use diodes to restrict the voltage amplitude of a signal. By placing diodes in parallel with the signal path, any voltage exceeding the diode's forward drop (plus any series reference voltage) is shunted to ground. This is essential for protecting sensitive inputs on microcontrollers or audio equipment from signal spikes.(3) Regulator Circuit (Voltage Stabilization)Zener diodes are the key component here. Unlike standard diodes, Zeners are designed to operate in the reverse breakdown region reliably. If the voltage across a Zener exceeds its "Zener Voltage" (Vz), it conducts heavily, clamping the voltage at that level. This makes them perfect for creating simple voltage references or low-power regulators.(4) Varactor Circuit (Tuning and Frequency Control)Varactor diodes (or Varicaps) act as voltage-controlled capacitors. When reverse-biased, the width of the depletion layer changes with voltage, which changes the junction capacitance. These are widely used in Voltage Controlled Oscillators (VCOs) for tuning radios, TVs, and mobile phones, as well as in frequency modulation (FM) circuits. 2.2 Typical Diode ApplicationsLight-emitting diode (LED)Figure 3. Light-emitting DiodeLEDs emit light when electrons recombine with holes at the PN junction, releasing energy in the form of photons. They have revolutionized lighting due to their safety, high efficiency, durability, and fast response time.Key Applications:1. Consumer Electronics: Backlights for LCD TVs, computer monitors, and smartphone screens.2. Automotive: Used in headlights, brake lights, and turn signals. Their fast switching speed improves safety (brake lights trigger faster than incandescent bulbs), and their longevity reduces maintenance.3. Industrial & Mining: Due to their robustness and efficiency, LEDs are replacing traditional lamps in harsh environments like underground mining.4. Urban Lighting: Replacing high-voltage, fragile neon tubes with LED strips for signage and architectural lighting reduces energy costs and fire risks.Zener diodeZener diodes maintain a constant voltage across their terminals when reverse-biased, even as current fluctuates. They are categorized by their breakdown voltage (e.g., 3.3V, 5.1V, 12V). They can be connected in series to achieve higher regulated voltages. Figure 4. Zener Diode CircuitRectifier diodeRectifier diodes allow current to flow only in one direction, converting Alternating Current (AC) into pulsating Direct Current (DC). This is the fundamental component of power supplies. Figure 5. Full Wave Rectifier CircuitLow Frequency (Mains): For standard 50Hz/60Hz rectification, the 1N400x or 1N540x series are standard. Key parameters are Maximum Rectified Current (Io) and Peak Inverse Voltage (PIV).High Frequency: In Switching Mode Power Supplies (SMPS), standard rectifiers are too slow. Fast Recovery Diodes (FRD) or Schottky diodes are required to handle high switching frequencies efficiently.Detector diodeDetector diodes (often Germanium or Schottky point-contact diodes) possess high detection efficiency and low junction capacitance. They are used to demodulate Amplitude Modulated (AM) signals in radios, extracting the audio signal from the carrier wave.  Figure 6. Detector Diode CircuitSchottky diodeA Schottky diode uses a metal-semiconductor junction rather than a P-N junction. This gives it two distinct advantages: 1. Low Forward Voltage Drop: Typically 0.15V to 0.45V (compared to 0.7V for Silicon), which reduces power loss and heat. 2. High Speed: Zero reverse recovery time makes them ideal for high-frequency switching power supplies, inverters, and motor drivers.Switching diodeDesigned specifically for rapid on/off operations. In the circuit below, VD1 acts as a switch to control the charging path of capacitor C2. Figure 7. Switching Diode CircuitFast recovery diode (FRD)FRDs are PN junction diodes doped to have a significantly reduced Reverse Recovery Time (trr). While a standard rectifier might take microseconds to stop conducting when voltage reverses, an FRD stops in nanoseconds. This is critical in modern power electronics like inverters and PWM controllers to prevent short-circuit currents. Update for 2025: In high-power applications, Silicon Carbide (SiC) diodes are increasingly replacing traditional silicon FRDs due to their ability to handle higher voltages and temperatures with almost zero switching loss.Transient voltage suppressor (TVS)Transient Voltage Suppressors (TVS) are specialized avalanche diodes designed to absorb high-energy spikes. They are the primary defense against ESD (Electrostatic Discharge) and voltage surges in sensitive electronics. Figure 8. Diode Circuit Symbols Ⅲ One Question Related to Diode Functions and Going Further3.1 QuestionWhy do we use diodes in a circuit?3.2 AnswerThe primary function is to serve as an electronic "check valve" or "one-way street" for electricity. This enables: 1. Rectification: Converting AC power (wall outlet) to DC power (batteries/electronics). 2. Protection: Blocking reverse polarity (if you put a battery in backward) or clamping high-voltage spikes (TVS). 3. Signal Manipulation: Demodulating radio signals or creating logic gates. 4. Reference: Providing a stable voltage reference (Zener). Ⅳ Diode Distributors RecommendationWhether you are sourcing standard rectifiers or advanced SiC power diodes, reliability is key. Here are some recommended sources for diode components:Mouser Electronics (Global Distributor)onsemi (Leading Manufacturer)KYNIX Semiconductor (Electronic Component Distributor)Digi-Key Electronics (Global Distributor) Frequently Asked Questions about Diode Function1. What is a diode used for?Its most common function is to allow electric current to pass in one direction (forward direction) while blocking it in the opposite direction (reverse direction). This is used for rectification, protection, and signal isolation. 2. What is the main function of a PN junction diode?It controls the flow of electrons. By manipulating the PN junction bias, it acts as a switch that is either ON (conducting) or OFF (insulating), depending on the direction of voltage applied. 3. What is the function of a rectifier diode?Rectifier diodes are specifically built to handle the conversion of AC (Alternating Current) to DC (Direct Current). They are robust enough to handle the high currents found in power supply units. 4. Do diodes output AC or DC?Diodes do not generate power. However, when an AC source is fed into a diode, the output is pulsating DC. The diode blocks the negative half of the AC cycle, leaving only the positive flow. 5. What is the function of a Zener diode?Zener diodes are used for voltage regulation. Unlike standard diodes, they are designed to conduct in reverse at a specific breakdown voltage (Vz). They are used to stabilize voltage rails and protect circuits from over-voltage surges. 6. What is the difference between a diode and a rectifier?"Diode" is the broad name for the component type (a two-terminal device). "Rectifier" is a function or a specific type of diode designed for power conversion. All rectifiers are diodes, but not all diodes are rectifiers (e.g., LEDs, Zener, and Varactors are diodes but are not used as rectifiers).