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If you want to save on your monthly electric bill and reduce your greenhouse gas emissions at the same time, you might buy a new, energy-efficient refrigerator. Or water heater. Or clothes dryer. But if you can only replace one of these, which will give you the biggest payback?You could try to figure that out by comparing the energy-use labels from your existing appliances with those of the models you might purchase—if you still have your old labels. Even then, the numbers may differ significantly from your actual usage, depending on factors such as age, condition, and your local climate. But soon, there could be a much easier way to figure out exactly how much power is being used by every appliance, lighting fixture, and device in your home, with pinpoint accuracy and at low cost, thanks to devices and software developed by researchers at MIT.The team's findings, developed over several years of intensive research, are described in a series of papers, including one published this week in the IEEE Sensors Journal, in a paper by MIT Professor of Electrical Engineering Steven Leeb and recent graduates David Lawrence MEng '16 and John Donnal PhD '16. Another paper from the team, which also includes as co-author James Paris PhD '13, is still in press.While many groups have worked on developing devices to monitor electricity use, the new MIT system has some key advantages over other approaches. First, it involves no complex installation: No wires need to be disconnected, and the placement of the postage-stamp-sized vibration sensors over the incoming power line does not require any particular precision—the system is designed to be self-calibrating. Second, because it samples data very quickly, the sensors can pick up enough detailed information about spikes and patterns in the voltage and current that the system can, thanks to dedicated software, tell the difference between every different kind of light, motor, and other device in the home and show exactly which ones go on and off, at what times.Own your own dataPerhaps most significantly, the system is designed so that all of the detailed information stays right inside the user's own home, eliminating concerns about privacy that potential users may have when considering power-monitoring systems. The detailed analysis, including the potential for specialized analysis based on an individual user's specific needs or interests, can be provided by customized apps that can be developed using the MIT team's system.Tests of the system have showed its potential to save energy and greenhouse emissions—and even to improve safety. One installation at a military base used for training exercises revealed that large tents were being heated all day during winter months, even though they were unoccupied for most of the daytime hours—a significant waste of money and fuel (which, in a combat setting, could be an important logistical concern). Another test installation, in a home, found an anomalous voltage pattern that revealed a wiring flaw that caused some copper plumbing pipes to carry a potentially dangerous live voltage."For a long time, the premise has been that if we could get access to better information [about energy use], we would be able to create some significant savings," Leeb says. He and his students have been tackling the problem for more than 10 years and bit by bit have found ways to circumvent the daunting problems involved in achieving this basic task.First was the ability to monitor changes in voltage and current without cutting the main incoming power line to a home or business (an expensive process requiring a licensed electrician) or plugging every appliance into a special monitoring device. Other groups have attempted to use wireless sensors to pick up the very faint magnetic and electric fields near a wire, but such systems have required a complex alignment process since the fields in some places can cancel each other out. The MIT team solved the problem by using an array of five sensors, each slightly offset from the others, and a calibration system that tracks the readings from each sensor and figures out which one is positioned to give the strongest signal.Interpreting the data flowThe next trick was in figuring out how to analyze the reams of data flowing in from the high-speed sensors, in order to tease out which bits correspond to current and voltage, and how that information could be used to identify "signatures" of specific appliances. This is possible because every motor or device has distinctive characteristics as to exactly how fast and how much the voltage varies, or spikes, at the moment the device switches on, or as it operates. After extensive testing in the lab, in homes, at the Fort Devens Army base outside Boston, and aboard the U.S. Coast Guard cutter Spencer, the team was able to develop a catalog of such signatures, to identify each kind of electrical load.And finally, given the prodigious amount of raw data generated by the system, the team had to figure out how to extract the useful information and display it in a way that would make it easy for people to make decisions about energy investments. They developed an interface that allows users to "zoom in" on specific time segments, revealing enough data to tell when a refrigerator turns on or off, or goes into its defrost cycle, or how often a water heater is switching on and off during the day."A bunch of major players have gotten into, and out of, this field," says Leeb, including giants like Google and Microsoft. But now, he says, the MIT team has solved the key issues and come up with a practical and very powerful system. One of the major insights they had was that keeping most of the data within the home and sending only small subsets out into the cloud for processing solved two problems at once: It eliminated the privacy concerns of using such a system, and it eliminated the huge bandwidth and data transmission costs that would be required if the raw data was sent to a central facility.Once the system is developed into a commercial product, Leeb says, it should cost only about $25 to $30 per home. "We're trying to lower the barriers to installation," says co-author John Donnal, and this noncontact sensor is simple enough for most home users to install on their own. "It just goes on with a zip tie," he says.William Singleton, an engineer at the U.S. Army Fort Devens Base Camp Integration Laboratory, who was not involved in this research, says this work "is an excellent example of how theoretical scientific and mathematical principles can be brought to bear on real world, practical, problem-solving applications." By using the MIT team's sensing system, he says, "significant potential savings in fuel, water, and equipment maintenance can be realized. This will provide increased options for the battlefield commander in accomplishing his mission, reduce the overall base camp logistics footprint, and ultimately save lives of warfighters involved in base camp sustainment and resupply." 

The ongoing research in the field of microelectronics and semiconductor microchips is made by Dr. Yue Kuo, professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, is continuing, which is evolving everyday technology such as cellphones, televisions, computers and more through the use of light emitting diodes (LED).Kuo's research group focuses on the development of semiconductors for micro and nano electronic uses. This has entailed working with technologies from television screens to devices like universal serial bus (USB) flash drives to make them faster, smaller and more power efficient.Kuo and his research group have developed a new type of LED known as a solid state incandescent light emitting device (SSI-LED). This device would emit light for an extended lifetime at a very low energy cost. Kuo currently has one of these LEDs his group has deployed that has been continuously emitting light for in excess of 18,000 hours. The development of these LED devices has progressed from the same kind of technology that powered the first incandescent light bulb developed by Thomas Edison."The chips used to make electronic devices work from the vacuum tube," Kuo said. "It was invented in 1907, and this tube was big. The first computer ever invented was made of thousands of these tubes. However, these vacuum tubes are not very reliable and the power consumption is very high and they burn out easily."Kuo explains that technology has leaped from the vacuum tube, to transistor, to the modern microchip, which enables scientists to fit billions and billions of transistors into a single chip. Beyond microchips are the semiconductors that Kuo primarily works with that form the essential computer hardware components of electronic circuits. While advanced, similar issues that plagued traditional vacuum tubes such as a short life span and energy inefficiency, still effect modern day semiconductors, according to Kuo."What I and my group have done is invented a new light bulb that is very similar in comparison to the leap from a vacuum tube to a computer chip," Kuo said. "We make a small chip with no vacuum that can emit light, but is so small, smaller than your fingernail, that it will not burn out after even 20,000 hours of use.For comparison, current larger incandescent light bulbs have a maximum lifespan of around 2,000 hours of use, meaning that Kuo's SSI-LED is both more energy efficiency and has greater device longevity than conventional technology in addition to being no bigger than a human fingernail. The SSI-LED that Kuo and his group have developed has many uses, one of which includes potentially using the light emitting technology to transfer electrical signals within computing devices. Kuo believes that a development of this magnitude would change the way everyday computer users are able to communicate with one another."The computer chips we have today are very fast, but as you know nothing satisfies us and no matter how fast we have, we want faster," Kuo said. "We've come, in terms of the modern design for computer chips, almost near the limit. The current speed is limited by how fast the signal is transmitted by metal. What we want to do is to transmit signals by light."The LED Kuo's group has invented is made out of silicon, giving it the potential to transmit signals in machines by light. This method would send signals tens of thousands of times faster than current transmission methods allow."SSI-lEDs are an extension of Edison's technology in a way," Kuo said. "Inside each are many, many small dots that emit light, each one is like Edison's lamp. The engineers in my group use chemical engineering training to make computer chips and transistors that we make into things like your LCD TV's that affect the lives of all people every day and that kind of potential is limitless." 

  In this article today, you will learn what transistor is, how does it work, how long is its history, and how many kinds of transistor are there, how to replace one when your transistor is broke and so many more. Say no more and off we go.     Catalog I. What is a Transistor? 1.1 General View 1.2 Transistor Structure and Operation II. Transistor History III. Transistor Development IV. Transistor Advantage V. Transistor Classification VI. Transistor Power Control VII. Transistor Test Replacement VIII. How to Judge the Electrode of a Transistor IX. Transistor Replacement Principle FAQ   I. What is a Transistor?   1.1 General View Transistors make our electronics world go round. They're critical as a control source in just about every modern circuit. Sometimes you see them, but more-often-than-not they're hidden deep within the die of an integrated circuit.    The transistor is a kind of solid semiconductor device. It has many functions, such as detection, rectifier, amplifier, switch, voltage stabilizer, signal modulation, and so on. As a variable current switch, transistors can control output currents based on input voltages. Unlike conventional mechanical switches (such as relay, switch), transistors use telecommunication signals to control their opening and closing, and the switching speed can be very fast, for example, the switching speed in the labs can be higher than 100GHz. Strictly speaking, transistors refer to all single components based on semiconductor materials, including diodes, transistors, field-effect transistors, silicon control, and so on. In addition, transistors usually mean crystal triodes.   The transistors are divided into two main categories: bipolar junction transistors (BJT) and field-effect transistors (FET).   The transistor has three poles. The three poles of bipolar junction transistor, composed of the emitter(made up of N-type and P-type), base, and collector respectively. For the field-effect transistors, they are the source, gate, and drain respectively.   Because the transistor has three polarities, there are also three ways to use them, namely, emitter grounding (called common emitter amplification, CE configuration), base grounding (called common base amplification, CB configuration), and collector grounding (called common set amplification, CC configuration, emitter-coupled logic). Transistors are semiconductor devices, which are commonly used as amplifiers or electrically controlled switches. Transistors are important components that regulate the operation of computers, mobile phones, and all electronic devices. Due to their high response speed and accuracy, transistors can be used for a wide variety of digital and analog functions design, including amplifiers, switches, and voltage stabilizers, signal modulation, and oscillator circuits. Transistors can be packaged independently or in a very small area, which can accommodate 100 million or more transistors integrated into a part of the circuit.   1.2 Transistor Structure and Operation   Transistors are made by stacking three different layers of semiconductor material together. Some of those layers have extra electrons added to them, which called “doping”, and others have electrons removed (doped with “holes” – the absence of electrons). A semiconductor material with extra electrons is called an N-type (negative) and a material with electrons removed is called a P-type (positive).    With some hand waving, we can say electrons can easily flow from N-regions to P-regions if they have a little force (voltage) to push them. But flowing from a P-region to an N-region is really hard (requiring more force—voltage).    The NPN transistor is designed to pass electrons from the emitter to the collector (the conventional current flows from collector to emitter). The emitter emits electrons into the base, which controls the number of electrons. In fact, most of the electrons emitted are “collected” by the collector, which sends them along to the next part of the circuit.   A PNP has a little special area. The base still controls current flow, but that current flows in the opposite direction, that is, from emitter to collector, instead of electrons, the emitter emits “holes” which are collected by the collector.   The transistor is kind of like an electron valve. The pin of the base is likely to a handle you can adjust to allow more or fewer electrons to flow from emitter to collector.     II. Transistor History   The invention of transistors can date back to the middle& later 1920s, an engineer Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in 1925, which was intended to be a solid-state replacement for the triode. Lilienfeld also filed identical patents in the United States in 1926 and 1928. However, it was limited to the technical level at the time, the material used to make it couldn’t meet the high-quality requirement, making it impossible to actually construct a working device at that time.   In December 1947, the first practically implemented device was a point-contact transistor invented by American physicists John Bardeen, Walter Brattain, and William Shockley from Bell Labs. Due to the complex manufacturing process of point-contact transistors, many products fail, and it also has disadvantages, such as high noise, difficulty to control when power is high and narrow application range. To overcome these shortcomings, Shockley put forward the idea of replacing metal-semiconductor contacts with a "rectifier junction", and they also proposed the working principle of it. The transistor revolutionized the field of electronics and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.   In 1950, the first P-N junction transistor came out, and its performance was exactly the same as the assumption of William Shockley. Most of today's transistors are still P-N junction transistors. (the so-called P-N junction is a combination of P-type and N-type, and P-type multiplex with holes, N-type multiplex with electrons.)   In the first test, it can amplify the audio signal 100 times, its shape is shorter than the firewood stick but thicker. In naming the device, Walter Brattain thought of its resistive conversion properties, that is, it works on a transfer current from "low-resistance input" to "high-resistance output," so it's called trans-resistor, later this abbreviated as a transistor.   The innovation of transistors was a major invention in the 20th century and the forerunner of the microelectronics revolution. Because the transistor is the key active component in practically all modern electronics. With it, a small, low-power-consuming electronic device can be used to replace a large, high-power-consuming electronic tube. What's more, the development of integrated circuits based on the invention of transistors.   In 2016, a team at Lawrence Berkeley National Laboratory broke the physical limit and cut the most sophisticated transistor process available from 14nm to 1nm, making a breakthrough in computing technology.   III. Transistor Development   1) vacuum triode In February 1939, there was a great discovery in the Bell Labs, the birth of a silicon PN junction. In 1942, a student, Seymour Benzer, was on a team led by Lark_Horovitz at Purdue University,  found that monocrystalline germanium has excellent rectifying performance which other semiconductors do not. These findings laid the groundwork for the later invention of transistors.    A triode is a vacuum tube with three electrodes which are cathode, anode, and a control grid. The function of an additional third electrode is to serve as an electrostatic screen that shields the cathode from the electrostatic field of anode triode is used for amplification of weak AC signals of frequency ranging from 0 to 100 MHz.   2) point-contact transistor The point-contact transistor is the first type of transistor to be successfully demonstrated. It was developed by research scientists John Bardeen and Walter Brattain at Bell Laboratories in December 1947. Bardeen and Brattain applied two closely-spaced gold contacts held in place by a plastic wedge to the surface of a small slab of high-purity germanium. The voltage on one contact modulated the current flowing through the other, amplifying the input signal up to 100 times. The group had been working together on experiments and theories of electric field effects in solid-state materials, with the aim of replacing vacuum tubes with a smaller device that consumed less power.   3) bipolar and unipolar transistors On the basis of bipolar transistors, Shockley put forward the concept of unipolar junction transistors in 1952, which is called junction transistors today. Its structure is similar to that of PNP or NPN bipolar junction transistors, but there is a depletion layer at the interface of P_N to form a rectifier contact between the gate and the conductive channels of source and drain. At the same time, both ends of the semiconductor as the gate to adjust the current between the source and drain.    4) silicon transistors The first working silicon transistor was developed at Bell Labs on January 26, 1954, by Morris Tanenbaum. The first commercial silicon transistor was produced by Texas Instruments in 1954. Silicon transistors and germanium transistors have the function of current amplification. The difference is that the threshold voltage(Even if the positive voltage is applied, it must reach a certain value before it can start to turn on. This is called threshold voltage, for silicon transistor, it is about 0.7V and for germanium transistor is about 0.3V) of silicon transistor is larger than that of germanium transistor; the reverse current of the silicon transistor is much smaller than that of the germanium transistor; the maximum operating temperature of the silicon transistor is higher than that of the germanium transistor; the stability of the silicon transistor is better than that of the germanium transistor.   5) integrated circuit (IC) After the invention of the silicon transistor in 1954, the great application prospect of the transistor has become more and more obvious. The next goal of scientists is how to connect transistors, conductors, and other devices efficiently. The invention of transistors gives birth to the integrated circuit as time requires. As we all know, an IC is a collection of electronic components—resistors, transistors, capacitors, etc.—all stuffed into a tiny chip and connected together to achieve a common goal today.   6) field-effect transistors(FET) and metal-oxide-semiconductor field-effect transistor(MOSFET) The field-effect transistor was first patented by Julius Edgar Lilienfeld in 1926 and by Oskar Heil in 1934, but practical semiconducting devices (the junction field-effect transistors) were developed later after the transistor effect was observed and explained by the team of William Shockley at Bell Labs in 1947. The basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925. In 1959, Dawon Kahng and Martin M. (John) Atalla at Bell Labs invented the metal-oxide-semiconductor field-effect transistor (MOSFET) as an offshoot to the patented FET design. In 1962, Stanley, Heiman, and Hofstein in an RCA device integrated study group found that a MOS tube can be constructed by a conductive strip, a high-resistance channel region, an oxide layer, and an insulating layer on a Si substrate through diffusion and thermal oxidation.   7) CPU A central processing unit (CPU), also called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions. But fewer people know that modern CPUs contain millions of individual transistors that are microscopic in size. Because transistors are the building blocks of the integrated circuits, and more transistors in CPUs means higher processing efficiency.     IV. Transistor Advantage   Compared with the electron tube, the transistor has many advantages:   （1）Fewer consumption No matter how good an electron tube is, it will gradually deteriorate due to changes in cathode atoms and chronic gas leakage. For technical reasons, the same problem existed at the beginning of transistor fabrication. With advances in materials and improvements in many ways, transistors live typically 100 to 1000 times longer than electron tubes.   Consumption of electric energy is only 1/10 or dozens of times of the electron tube. It does not require heating the filament to produce free electrons like an electron tube. For example, a transistor radio can be listened to for half a year or more long with a few dry batteries, which is difficult for an electronic tube radio.   （2）No need to preheat Work as soon as you turn on the machine. For example, a transistor radio, you can hear the sound as soon as it turns on, and pictures come up quickly when turn on a transistor TV. But electron tube equipment cannot do this. Obviously, transistors have great advantages in electric equipment, medical treatment, industrial measurement, etc.   （3）Solid and reliable More reliable than the tube because of its shock resistance and vibration resistance. In addition, transistors release less heat due to their smaller size, so they can be used in small, complex, reliable circuits. Although the fabrication process of transistors is precise, the process is simple, it is helpful to increase the installation of it on the devices.   （4）Importance Transistors are the key active components in all modern electrical appliances. The importance of transistors in today's society is mainly due to their ability to use highly automated processes for mass production, which greatly reducing unit production costs.   While millions of monolithic transistors are still in use, but most transistors are assembled on microchips (chips) with diodes, resistors, and capacitors to make complete circuits. Analog or digital design or both are integrated on the same chip. The cost of designing and developing a complex chip is quite high, but the price per chip is minimal when the cost apportioned to millions of units.     V. Transistor Classification   According to material The semiconductor material used as a transistor can be divided into silicon material transistors and germanium material transistors. Furthermore, the polarity of the transistor can be divided into four types: germanium NPN transistors and PNP transistors, silicon NPN transistors, and PNP transistors.   According to craft Transistors can be divided into diffusion transistors, alloy type transistors, and planar transistors according to their structure and fabrication process.   According to the current capacity Transistors can be divided into low-power transistors, medium-power transistors, and high-power transistors by current capacity.   According to service frequency Transistors can be divided into low-frequency transistors, high-frequency transistors, and ultra-high-frequency transistors.   According to packaging Types The transistors can be divided into metal, plastic, glass, and ceramic packaging transistors.   According to applications Transistors can be divided into low noise amplification transistors, middle and high-frequency amplification transistors, low-frequency amplification transistors, switching transistors, Darlington transistors, high reversion voltage transistors, damping transistors, phototransistors, and magnetic sensitive transistors, and so on.   The low cost, flexibility, and reliability of transistors make them the general choice for non-mechanical tasks, such as digital computing. In the control of electric appliances and machinery, transistor circuits are also replacing motor equipment because of its lower cost and high efficiency.   Specific Types Expressions   1) transistors It is a semiconductor device with two PN junctions inside and usually three eliciting electrodes outside. The transistor is divided into two main categories: bipolar junction transistor (BJT) and field-effect transistor (FET), which have slight differences in their application in a circuit. A bipolar junction transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter. For a field-effect transistor, the terminals are labeled gate, source, and drain, and voltage at the gate can control the current between source and drain.   2) giant transistor The power transistor is a high voltage, high current bipolar transistor (Bipolar Junction Transistor-BJT), so it is sometimes called Power BJT; its characteristics are: high voltage, high current, good switching characteristics, but the driving circuit is complex, driving power is large; the principle of GTR and ordinary bipolar junction transistor is the same.   3) phototransistor The phototransistor is a device that is able to sense light and alter the current flowing between emitter and collector according to the level of light it receives.   Phototransistors and photodiodes can both be used for sensing light, but the phototransistor is more sensitive in view of the gain provided by the transistor. This makes phototransistors more suitable in a number of applications.   Phototransistors adopt the basic transistor concept as the basis of their operation. In general, a phototransistor can be made by exposing the semiconductor of an ordinary transistor to light. Phototransistors were made by not covering the plastic encapsulation of the transistor with black paint in the early stage.   4) bipolar transistor This is a transistor widely used in audio circuits. The bipolar means the flow of current in two kinds of semiconductor materials. Bipolar transistors can be divided into NPN type or PNP type according to the polarity of operating voltage.    5) bipolar junction transistor—BJT The bipolar junction transistor (BJT) is a type of transistor that uses both electron and hole charge carriers. On the contrary, unipolar transistors, such as field-effect transistors, only use one kind of charge carrier. For their operation, BJTs use two junctions between two semiconductor types, N-type and P-type.   BJTs have two types, NPN and PNP, and are available as individual components, or fabricated in integrated circuits, often in large numbers.   BJTs have an amplification function, concretely, they can amplify current, mainly depending on its emitter current transmission through the base area to the collector. To ensure this transmission process, on the one hand, it requires to meet the internal conditions, that is, the impurity concentration in the emission region needs much larger than the impurity concentration in the base region, and meanwhile, the thickness of the base region should be very small.   On the other hand, the external conditions should be satisfied, that is, the emission junction should be positive bias (adding positive voltage), and the collector junction should be inversely biased. This allows BJTs to be used as amplifiers or switches, giving them wide applicability in electronic equipment, including computers, TVs, mobile phones, audio amplifiers, industrial control, radio transmitters, and so on.   There are many kinds of BJT, according to frequency, high frequency, low frequency, according to power, small, medium, high power, according to the semiconductor material, silicon, and germanium tube. The amplifier circuit consists of the common emitter, common base, and common collector.   6) field-effect transistor(FET) The meaning of "field effect" is that the principle of the transistor is based on the electric field effect of the semiconductor. The field-effect refers to the modulation of the electrical conductivity of a material by the application of an external electric field.   There are two main types of FET: junction FET (JFET) and metal-oxide-semiconductor FET (MOS-FET). Unlike BJT, FET is conducted by only one carrier, therefore, it is also known as a unipolar transistor. It belongs to voltage-controlled semiconductor devices that have the advantages of high input resistance, low noise, low-power consumption, wide dynamic range, easy integration, no secondary breakdown, wide safe working area, and so on.   In a metal, the electron density that responds to applied fields is so large that an external electric field can penetrate only a very short distance into the material. However, in a semiconductor, the lower density of electrons (and possibly holes) that can respond to an applied field is sufficiently small that the field can penetrate quite far into the material. This field penetration alters the conductivity of the semiconductor near its surface and is called the field effect. The field-effect underlies the operation of the Schottky diode and of field-effect transistors, notably the MOSFET, the JFET, and the MESFET.   The field effect is to change the direction or magnitude of the applied electric field perpendicular to the surface of the semiconductor to control the density or type of most carriers in the conducting layer (channel) of the semiconductor. The current in the channel is modulated by voltage, and the working current is transported by most carriers in the semiconductor. This type of transistor, which has only one polar carrier to conduct electricity, is also called a unipolar transistor.    Compared with bipolar transistors, FET is widely used in various amplifiers, digital circuits, and microwave circuits because of its high input impedance, low noise, high limit frequency, low power consumption, simple manufacturing process, and good temperature characteristics.    7) static induction transistor The static induction transistor(SIT), which was born in 1970, is actually a junction field-effect transistor. A high-power SIT device can be made by changing the transverse conductive structure of a small-power SIT device used for information processing into a vertical conductive structure. The operating frequency of SIT is comparable to that of the power MOSFET, or even higher than that of the electric MOSFET. The power capacity is also larger than the power MOSFET, so it is suitable for high-frequency and high-power devices. At present, it has been used in radar communication equipment, ultrasonic power amplification, pulse power amplification, and high-frequency induction heating, and so on.   However, the SIT is conducted when no signal is added to the gate, and the gate is turned off when the negative bias is applied, which is called the normal on-type device, thus it is inconvenient to use. In addition, due to the large on-state resistance and consumption of SIT, it has not been widely used in most power electronic devices.   8) single-electron transistor A kind of transistor that can record signals with one or a small number of electrons. With the development of semiconductor etching technology, more and more large-scale integrated circuits can be made. It is considered an important component of nanotechnology, single-electron transistors provide high operating speed and low power consumption.   Single-electron transistors are usually made by keeping two tunnel junctions in series. The transistor consists of a source electrode and a source-drain, which is joined with the help of a tunneling island that is also connected to a gate capacitively. The electrons can flow to another electrode only through the insulator. There are two categories of single-electron transistors: metallic and semiconducting. The former makes use of a metallic island, and its electrodes using a shadow mask are mostly evaporated onto an insulator. The latter, on the contrary, depends on severing the two-dimensional electron gas that forms at the interface of the semiconductors for the junction.   Insulated-gate bipolar transistor(IGBT) is also a three-terminal device: gate, collector, and emitter. It combines the advantages of the giant transistor and power MOSFET. Therefore, it is widely used in many fields due to its sound characteristics.   a. main parameters The main parameters of the transistor include current magnification factor, dissipation power, frequency characteristic, maximum collector current, maximum reverse voltage, reverse current, and so on.   b. amplification coefficient DC current magnification factor also called static current magnification factor or DC magnification factor. It refers to the ratio of transistor collector current to base current, which is usually expressed by hFE or β when the static signal input is not changed.   c. ac magnification AC magnification also called AC current magnification factor or dynamic current magnification factor. It refers to the ratio of transistor collector current variation to base current variation in AC state. In addition, the two parameters are close at a low-frequency state.   d. dissipation power Dissipation power is also called the maximum allowable dissipation power of the collector, which refers to the maximum dissipation power of the collector when the transistor parameter does not exceed the prescribed allowable value.   The dissipation power is closely related to the maximum allowable junction and collector current of the transistor. The actual power consumption of transistors is not allowed to exceed the maximum allowable dissipation power value, otherwise, the transistor will be damaged by overload.   The transistor whose dissipation power is less than 1W is usually called the low-power transistor, that value is equal to or greater than 1W, and less than 5W, such transistor is called the medium-power transistor; whose value is equal to or greater than 5W is called the high-power transistor.   When the operating frequency of the transistor exceeds the cutoff frequency fβ or fα, the current amplification factor β will decrease with the increase of characteristic frequency fT(fT refers to the operating frequency of the transistor when the β value is reduced to 1).   Usually, the transistors whose fT is less than or equal to 3MHZ are called low-frequency transistors; transistors whose fT is greater than or equal to 30MHZ are called high-frequency transistors; those whose fT is greater than 3MHZ and less than 30MHZ are called intermediate frequency transistors.   e. maximum frequency fM The maximum oscillation frequency is the corresponding frequency when the power gain of the transistor is reduced to 1. In general, the maximum oscillation frequency of high-frequency transistors is lower than the common base cutoff frequency fα, while fT is higher than the cutoff frequency fα of the common base and lower than the cutoff frequency fβ of the common collector.   f. maximum current Collector maximum current is the maximum current allowed by transistor collector. When the collector current of the transistor exceeds it, the β value of the transistor will change obviously, which will affect the normal operation of the transistor and even damage it.   g. maximum reverse voltage Maximum reverse voltage is the maximum operating voltage that the transistor is allowed to apply. It includes collector-emitter reverse breakdown voltage, collector-base reverse breakdown voltage, and emitter-base reverse breakdown voltage.   (1) Collector-collector reverse breakdown voltage This voltage refers to the maximum allowable reverse voltage between the collector and emitter when the base of the transistor is open circuit, usually expressed in VCEO or BVCEO.   (2) Base-base reverse breakdown voltage This voltage refers to the maximum allowable reverse voltage between the collector and the base when the transistor emitter is open circuit, expressed in VCBO or BVCBO.   (3) Emitter-emitter reverse breakdown voltage This voltage refers to the maximum allowable reverse voltage between the emitter and the base when the collector of the transistor is open circuit, expressed in VEBO or BVEBO.   (4) ICBO: reverse current between collector and base electrodes ICBO, also called collector junction reverse leakage current. It refers to the reverse current between collector and base when the emitter of the transistor is open circuit. ICBO is sensitive to temperature, thus the smaller the value is, the better the temperature characteristic of the transistor is.   (5) ICEO: the reverse breakdown current between collector and emitter refers to the reverse leakage current between the collector and emitter when the base of the transistor is open. The smaller the current, the better the performance of the transistor.   h. switches It is a most fundamental application of a transistor is using it to control the flow of power to another part of the circuit, that is, using it as an electric switch. Applying it in either cutoff or saturation mode, the transistor can create the binary on/off the effect of switches.   A transistor switch is a critical circuit-building block; it is used to make logic gates, which go on to create microcontrollers, microprocessors, and other integrated circuits.   VI. Transistor Power Control   Today's power transistors can control hundreds of kilowatts of power, and using power transistors as switches has many advantages, mainly as follows:   (1) Easy to turn off and few auxiliary components needed. (2) The switching speed is quick and works at a very high frequency. (3) The voltage resistance range is wide.     Performance improvement of power transistors. Such as:   (1) An increase in the effective working area of switching transistors. (2) Technical processing simplification. (3) Recombination of transistors. (4) The progress of base driving technology for the high power switch. Today's base driving circuits not only drive power transistors but also protect power transistors, which are called "non-centralized protection" (as opposed to centralized protection). The functions of the integrated drive circuit include:   (1) Turning-on and turning-off power switches. (2) Monitoring auxiliary power supply voltage. (3) Limiting maximum and minimum pulse width. (4) Thermal protection. (5) Monitoring saturation voltage drop of switches.     VII. Transistor Test Replacement   The transistors in the circuit mainly include crystal diode, transistor, thyristor, field-effect transistor, and so on. The most commonly used transistor and diodes are the transistor and diode. How to correctly judge the good or bad of the transistors is one of the keys to maintenance.   The key function of an ideal diode is to control the direction of current flow. Current passing through a diode can only go in one direction, called the forward direction. Currently trying to flow the reverse direction is blocked. They’re like the one-way valve of electronics.   If the voltage across a diode is negative, no current can flow, and the ideal diode looks like an open circuit. In such a situation, the diode is said to be off or reverse biased.   As long as the voltage across the diode isn’t negative, it’ll “turn on” and conduct current. Ideally, a diode would act like a short circuit (0V across it) if it was conducting current. When a diode is conducting current it’s forward biased (electronics jargon for “on”).   First of all, we should know whether the diode belongs to a silicon tube or a germanium tube. The forward voltage drop of the germanium tube is generally between 0.1~0.3V, while that of the silicon tube is generally between 0.6~0.7V. The method of measurement is as follows: two multimeters are used. one multimeter is used to measure the forward resistance and another multimeter is measuring the voltage drop of its tube. Therefore, whether germanium tube or silicon tube can be judged according to the voltage drop values. In addition, the greater the difference between the positive and negative resistance of the measured diode, the better.    For example, the forward resistance is several hundred or thousands of ohms, and the reverse resistance is more than tens of kilos, it can be concluded that the diode is good. And meanwhile, the positive and negative electrodes of the diodes can be determined: when the measured resistance values are hundreds of ohm or thousands of ohm, it indicates that is the positive resistance. In addition, if the forward and backward resistance is infinite, it indicates the internal breakage; if the forward and backward resistance is the same, there is also a problem with such a diode; and the forward and backward resistance is zero to indicate the short circuit.   Crystal Triode: It mainly plays an amplification role, so how to determine the amplification capacity? The method is as follows: the multimeter is adjusted to the level R×100 or R×1K. When the NPN tube is measured, the positive meter pen is connected with the emitter and the negative meter pen is connected with the collector, the finally measured value should be thousands of ohm. Then a 100kΩ resistor is connected in series between the base and collector, and the resistance measured by the multimeter should be significantly reduced. The greater the change, the stronger the amplification ability of the transistor. If the change is small or no change at all, that means the transistor does not have amplification ability or this ability is very weak.     VIII. How to Judge the Electrode of a Transistor   Using R×100 level of multimeter germanium transistors to measure and for silicon transistors is R×1K. The red meter pen is in contact with an electrode, and the other two electrodes are measured by a black meter pen. If you can’t find two small resistors, you can move the red meter pen to the other electrodes to measure continuously. Neither works, you can move the black meter pen.   When two small resistors are found, the measuring electrode of the fixed meter pen is the base. If the fixed meter pen is a black pen, the transistor is the NPN type, and if the fixed one is a red pen, the transistor is a PNP type.     A. method for judging resistances of collector and emitter A multimeter is used to measure the resistance at the extreme poles of the base removal, and the exchange meter pen is measured twice. In the case of a germanium tube, the smaller resistance is measured for the first time. In the case of the PNP type, the black meter pen is connected to the emitter, and the red meter pen is connected with a collector electrode as if it is an NPN type. The black meter pen is connected to the collector, the red meter pen is connected to the emitter; If it is a silicon tube, the first time the measured resistance is larger if it is PNP type, the black meter pen is connected with the emitter, the red meter pen is connected with the collector, if the type is NPN, the black meter pen is connected with the collector, and the red meter pen is connected with the emitter.   B. PN junction forward resistance method Measuring the forward resistance of two PN junctions, the value of the emitter is larger and the value of the collector is smaller.   C. amplification coefficient method Using the two-meter pens of the multimeter to contact the two electrodes except for the base, if it is PNP, using the finger to touch the base and the electrode that red meter pen connected to see the swing of the pointer. Change the meter pens to test again, selecting the large swing. At this time, the electrode of the red meter pen connected is the collector. If it is NPN, using the finger to touch the base and the electrode that the red meter pen connected to see the swing of the pointer. Change the meter pens to test again, selecting the large swing, at this time, the electrode of the black meter pen connected is the collector.   Note: The between analog multimeter and the digital multimeter is different. For the analog multimeter, the red meter pen is connected to the negative pole of the power supply, whereas the digital meter is the opposite.     IX. Transistor Replacement Principle   The replacement principle of transistors can be summarized as three: same type, similar characteristics, and similar appearance.   One—same type 1.The material is the same, that is, the germanium tube replaces the germanium tube, silicon tube replaces the silicon tube.   2.The polarity is the same, that is, NPN-type tube replaces NPN-type tube and PNP-type tube replaces PNP-type tube.    Two—similar characteristics The characteristics of the transistors used for replacement should be similar to those of the original transistors, and their main parameter values and characteristic curves should not differ much.    1. Maximum DC dissipation power (PCM) of collector board   PCM of the replaced transistor is generally required to be equal to or larger than the original transistor. However, in a practical test, if the actual DC dissipation power of the original transistor in the whole circuit is much smaller than its PCM, it can be replaced by a transistor with a smaller PCM.   2. Maximum allowable DC current (icm) of collector   Icm of replacing transistor is generally required to be equal to or larger than the original transistor.   3. Breakdown voltage   Transistors for replacement must be able to withstand the maximum operating voltage throughout the machine.   4. Frequency characteristics   The frequency characteristic parameters of transistors are as follows:   (1) characteristic frequency ft: it refers to the frequency when the test frequency is high enough of the common emitter current magnification factor. (2) cutoff frequency fb: When replacing transistors, the main consideration is ft and fb. Transistors usually required for replacement should not be less than the corresponding ft and fb of the original one.   5. Other parameters   In addition to the above main parameters, for some special transistors, the following parameters should be taken into consideration when replacing:   (1) For low noise transistors, transistors with small or equal noise coefficients should be used in replacement. (2) For transistors with automatic gain control performance, transistors with the same automatic gain control characteristics should be used during replacement. (3) For the switch tube, the related switching parameters should be considered when replacing the switch tube.    Three—similar appearance The small power transistors are similar in shape, so long as the lead line of each electrode is marked clearly, and the order of the lead line is the same as that of the tube to be changed, it can be replaced. The appearance of high-power transistors is quite different. In order to install well and maintain normal heat dissipation conditions, the transistors with similar appearance and same size should be selected for replacement.   FAQ   1. What is a transistor and how does it work? A transistor is a miniature electronic component that can do two different jobs. It can work either as an amplifier or a switch: When it works as an amplifier, it takes in a tiny electric current at one end (an input current) and produces a much bigger electric current (an output current) at the other.   2. What are transistors used for? Transistor, semiconductor device for amplifying, controlling, and generating electrical signals. Transistors are the active components of integrated circuits, or “microchips,” which often contain billions of these minuscule devices etched into their shiny surfaces.   3. What is transistor and its types? Transistors are a three terminal semiconductor device used to regulate current, or to amplify an input signal into a greater output signal. ... There are a varieties and different types of transistors available in today's market including Bipolar, Darlington, IGBT, and MOSFET Transistors.   4. What is the principle of transistor? A transistor consists of two PN diodes connected back to back. It has three terminals namely emitter, base and collector. The basic idea behind a transistor is that it lets you control the flow of current through one channel by varying the intensity of a much smaller current that's flowing through a second channel.   5. What are the two main applications of transistor? Transistors are commonly used in digital circuits as electronic switches which can be either in an "on" or "off" state, both for high-power applications such as switched-mode power supplies and for low-power applications such as logic gates.   6. What is PNP and NPN transistor? In an NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to the emitter. In a PNP transistor, a positive voltage is given to the emitter terminal to produce current flow from the emitter to collector.   7. Why is more transistors better? By squeezing more transistors into a smaller space, a microprocessor can be produced which does more work in less time (more powerful). It also allows one chip to perform more functions - what used to require several chips can all fit into one chip.   8. How do you read a transistor? The typical format for the transistor is a digit, letter and serial number. The first digit is the number of leads minus one. An ordinary bipolar transistor has three leads, so the first digit for it will be 2. The letter N is for semiconductors, so this will be the letter written on a transistor using this system.   9. How do you connect two transistors together? Two NPN transistors can be connected in series with the collector of the lower transistor connected to the emitter of the upper transistor, figure 4, which provides a way to switch off the load from two different signals. Either input can turn off the load but both need to be on for the load to be on.   10. Are smaller transistors faster? The smaller the transistor, the smaller the gate, and the less charge you have to move around. Fourth, you can make the chip faster. The FET effect is not instantaneous, there is a propogation delay involved. Smaller transistors have a shorter delay, so you can operate at higher clock frequencies.     You May Also Like Basic IGBT Tutorial: Short-circuit Protection and Driving Circuit

Vendors and consumers can agree: connectivity matters, and not just poetically speaking, or in the context of social networking. As for many, staying digitally connected is quite real a requirement and has become a lifeline of its own, in terms of ability to do work and in terms of access to vital information. San Diego-based Ethertronics is a business that provides connectivity via antenna and RF systems solutions. On Tuesday the company announced news of an active steering IC, with embedded processor for Multiple Input Multiple Output (MIMO) applications. This is the EC482, with potential impact on cable and satellite markets. The company said its team can integrate EC482 products, including access points, set-top boxes, WiFi clients, WiFi extenders, wearables and other Internet of Things (IoT) devices.Translating what this means, Gigaom's senior writer Kevin Fitchard, who covers mobile broadband, carriers and wireless technologies, said that the new chip from Ethertronics "will bring its active steering algorithms to Wi-Fi antennas, increasing their range and boosting their throughput in less than optimal conditions." Ethertronics Chief Scientist Jeff Shamblin told Firchard that with the new version of the EtherChip, "active steering helps signals navigate multiple walls and ceilings which often separate a router from a Wi-Fi device."Quoted in RCR Wireless News, Shamblin, referring to the Active Steering technology, said, "Now that we can dynamically control the radiation pattern, not only can we improve the communication link you're trying to establish, we can start to null out interfering sources, so it brings interference mitigation."The EE Times explained that the company was leveraging its experience developing embedded antennas to create a line of dedicated beamforming chips. "Algorithms on EC482's processor monitor RF link performance on a wireless device to generate up to four radiation patterns and select the optimal antenna for the best performance," wrote Jessica Lipsky, associate editor. "The company's EtherChip EC482 aims to improve RF signal for Wi-Fi and 5 GHz backend applications."The company said the EtherChip EC482 had "superior single- and multi-antenna performance at frequencies even beyond the WiFi high-band." The operating frequency range is 100 MHz to 7000 MHz. The small footprint is just 3.0 x 3.0 x 0.75 mm3 in a QFN 24-pin package. Very low power consumption is required for operation, said the news release, which makes the EC482 suitable for even battery-operated systems.Ethertronics will show its new EtherChip EC482 and "Active Steering" solutions during Mobile World Congress next month in Barcelona.Laurent Disclos, Ethertronics CEO, shared his predictions in January for the new year in RCR Wireless News. "Regardless of the application – streaming a favorite show via a 5 GHz set-top box, keeping tabs on one's health via a wearable, or simply placing a voice call via a smartphone – the antenna is the only RF sensor in a wireless device, and those of us working to make that heartbeat stronger will have an exciting year in 2015, and beyond." 

Seldom women are interested in circuit boards. However, Susan Stockwell, the artist from England, has changed our mind. She loves circuit board and knows even better men. She makes the world map using the electronic circuit board. Besides, she tried her best to correspond the color of real landscape to the electronic components.    

In the article today, we will introduce you all about diodes, what is this component and what are its characteristics, where to use it, etc.   Understand what diodes are and what they do in this video Catalog   I. What is a Diode? II. Diode Characteristics III. Diode Application IV. Diode Types V. Diode Conductive Property VI. Diode Parameters VII. Diode Testing FAQ   I. What is a Diode?   In electronic components, a diode is a device with two terminals. The most common function of diodes is to allow primarily the current to pass in one direction (called forward bias) and reverse blocking (known as reverse bias), which called asymmetric conductance. This characteristic of the current directionality of most diodes is commonly referred to as the rectifying function. The most common diodes made today are semiconductor materials such as silicon or germanium. The package of transistors has glass, plastic, and metal commonly. In the early stage, the vacuum electron diode is an electronic device that can transmit current as unidirectional conduction. There is a PN junction and two lead terminals inside the semiconductor diode and it has unidirectional current conductivity according to the direction of the applied voltage. But the crystal diode is a p-n junction interface formed by the sintering of p-type semiconductor and n-type semiconductor, and a space charge layer is formed on both sides of the interface to form a built-in field. When the applied voltage is zero, the diffusion current caused by the concentration difference between the carriers on both sides of the p-n junction is equal to the drift current caused by the self-built electric field. This is a common characteristic of diodes in normal conditions.   II. Diode Characteristics   1. Forward direction When the forward voltage is applied, it is small in the starting part of the forward characteristic, which is not enough to overcome the blocking effect of the electric field in the PN junction, and the forward current is almost zero, which is referred to as the headband. This forward voltage, which cannot lead the diode, is referred to as a deadband voltage. When the forward voltage is greater than the deadband voltage, the electric field blocking in the PN junction is overcome, and the diode is in conduction, and the current rises rapidly with the increase of the voltage. In the normal current range, the terminal voltage of the diode is almost unchanged at the time of conduction, which is referred to as the forward voltage of the diode. When the forward voltage across the diode exceeds a certain value, the internal electric field is rapidly weakened, in the case of this situation, the current increases rapidly and the diode leads forward, which called threshold voltage, and silicon tube is about 0.5V, germanium tube is about 0.1V, in addition, the forward on-voltage drop of silicon diode and germanium diode is about 0.6~0.8V and 0.2~0.3V respectively.   2. Reverse direction When the applied reverse voltage does not exceed a certain range, the current passing through the diode is the reverse current formed by the minority current carrier drift motion. Because the reverse current is very small, the diode is in a cut-off state. This is also called reverse saturation current or leakage current, and it is greatly affected by temperature. In general, the reverse current of silicon tubes is much smaller than that of germanium tubes. The reverse saturation current of low power silicon tube and low-power silicon tube is in the order of nA and the low-power germanium tube is in the order of μA. When the temperature increases, the number of current carriers increases, and the reverse saturation current increases when the temperature is rising.   3. Breakdown When the applied reverse voltage exceeds a certain value, the reverse current increases suddenly, which is called electric breakdown. The critical voltage that causes the breakdown is called the reverse breakdown voltage of diodes. When the electric breakdown occurs, the diode loses its unidirectional conductivity. If the diode is not overheated by electric breakdown, the unidirectional conductivity will not necessarily be permanently destroyed. After removing the applied voltage, its performance can still be restored. If not, the diode is damaged. Therefore, the reverse voltage should be avoided too high when using diodes.   Reverse: the reverse breakdown of the PN junction is divided into Zener breakdown and avalanche breakdown:   a. Zener breakdown  The reverse breakdown is divided into Zener breakdown and avalanche breakdown according to the mechanism. In the case of high doping concentration, when the width of the barrier region is very small and the reverse voltage is large, the covalent bond structure in the barrier region is destroyed, the shared electron is separated from the covalent bond binding, and the covalent electron-hole is produced, which results in the sharp increase of the current. This phenomenon is called Zener breakdown. If the doping concentration is low, and the width of the barrier is wider, which will not result in Zener breakdown easily.   b. Avalanche breakdown  Another breakdown is avalanche breakdown. When the reverse voltage is increased to a larger value, the external electric field accelerates the electron drift speed in the transition region, thus the valence electron in the covalent bond is collided out of the covalent bond by electric field electrodes, which produces a mobile or free electron-hole pair. The newly generated electron-hole is accelerated by the electric field and then bumped out of other valence electrons again. The carrier increases like an electron avalanche, resulting in a sharp increase in the current, which is called avalanche breakdown. Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials.   Regardless of the breakdown, if the current is not limited, it may cause permanent damage to the PN junction.   4. Voltage drop Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance. Diode voltage drop: forward voltage drop silicon diode (no light-emitting type) is 0.7V, the forward voltage drop of germanium tube is 0.3V. In addition, the forward tube voltage drop of LED will vary with different light-emitting colors. But there are three main colors, the specific reference values are as follows:    red LED is 2.0~2.2V yellow LED is 1.8~2.0V green LED is 3.0~3.2V   The rated current of normal luminescence is about 20mA.   The relation of voltage and current of the diode is not linear, therefore, it is necessary to select resistors properly in parallel with different diodes.   5. Characteristic curve As above mentioned, the diode has a unidirectional conductivity. Applying a forward voltage to the diode, when the voltage value is small, the current is very small, and when the voltage exceeds 0. 6V, the current starts to increase exponentially, which is generally referred to as the opening voltage of the diode. When the voltage reaches about 0.7V, the diode is in a fully conductive state, and this voltage is generally referred to as the conduction voltage of the diode and is indicated by the symbol UD.   For germanium diodes, the turn-on voltage is 0.2V and the on-voltage UD is about 0.3V. A reverse voltage is added to the diode: when the voltage is small, the current is small, and this referred to as the reverse saturation current IS. When the reverse voltage exceeds a certain value, the current begins to increase sharply, called reverse breakdown, and meanwhile, the voltage of this phenomenon occurred is called the reverse breakdown voltage of the diode, which is represented by the symbol UBR. The UBR values of different types of diodes vary greatly, ranging from dozens of volts to kilowatts.     III. Diode Application   1. General Principle The main function of a diode is to allow an electric current to pass in one direction (forward direction) and blocks it in the opposite direction (the reverse direction). Based on this function, the diode can be viewed as an electronic check valve. This unidirectional action is called rectification, which is used to transform alternating current (AC) to direct current (DC).   What's more, diodes also have other complicated behaviors than this simple on-off action(their nonlinear current-voltage characteristics as above mentioned). Diodes can conduct electricity if a certain threshold voltage or cut-in voltage is added in the forward direction (forward-biased). And the voltage drop across a forward-biased diode varies slightly with the current, which is affected by temperature; this effect can be used as a temperature sensor or as a voltage reference. In addition, diodes' high resistance to current flowing in the reverse direction drops to a low resistance sharply when the reverse voltage across the diode reaches a value called the breakdown voltage.    The current-voltage characteristic of semiconductor diodes can be fixed by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture. And these technical indexes are used to create special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage, to protect circuits from high voltage surges, to electronically tune radio and TV receivers, to generate radio-frequency oscillations, and to produce light.     2. Operational Principle In this video, we will explore the inner workings and applications of the diode in great detail. Apart from the basic working of the diode, this video also explains V-I characteristics and applications of diode (rectification using Bridge rectifier) with help of animation.   The crystal diode is a PN junction formed by p-type semiconductors and n-type semiconductors, and a space charge layer is formed on both sides of the interface with a self-built electric field. When there is a positive voltage bias, the mutual suppression of the external electric field and the self-built electric field leads to the increase of the carrier diffusion current and then the positive current caused by this interaction between them. When there is a reverse voltage bias, the external electric field and the self-built electric field are further strengthened, forming in a certain reverse voltage range independent of the reverse bias voltage, and the reverse saturation current be generated. When the applied reverse voltage excesses a certain value, the electric field intensity in the space charge layer of PN junction reaches the critical value to cause the multiplying process of carriers, resulting in a large number of electron-hole pairs and a very large reverse breakdown current, which is called a breakdown phenomenon of diodes.     3. Specific Explanations There are many types of diodes, and according to electronic fabrication, the following diodes are often used: Zener diodes for voltage regulators, switching diodes for digital circuits, various for resonance, and so on. The most common diode is the light-emitting diode. Light-emitting diodes (LEDs) are widely used in various electronic products, light sources for optical fiber communication, indicators, and lighting for various instruments. LEDs have many characteristics which can not be compared with ordinary light-emitting devices. These characteristics include safety, high efficiency, environmental protection, long life, fast response speed, small size, and solid structure. And the following are some of their main applications:   1) Application summary   (1) In electronic equipment LEDs are generally used in electronic devices as backlight or display, lighting applications. Displays ranging from large LCD televisions, computer displays, and media players such as MP3, MP4, and mobile phones.   (2) In the automobile and large machinery The light-emitting diode is widely used in automobiles and large machinery. Light-emitting diodes are used in the direction lights, in-vehicle lighting, mechanical equipment instrument lighting, large-light, turn-light, brake light, tail lights, and so on. It is mainly because the response of the light-emitting diode is fast and the service life is long (the service life of the general light-emitting diode is longer than that of the service life of automobiles and large machinery).   (3) In coal mine Owing to the advantages of high efficiency, low energy consumption, long life, strong luminosity and so on, LEDs are used in miner lighting devices. Although not fully popularized, it will be widely used in the near future, and LEDs will replace common light-emitting devices in coal mine applications.   (4) In decoration lights of the city Neon is an important symbol of modern urban prosperity, but there are many shortcomings, such as a short life span. Therefore, there are many advantages in replacing neon with LED. Compared with neon, LEDs not only have a longer life, but also save energy, be easily driven and controlled, and do not need maintenance. It is the inevitable result of LED equipment to replace the neon lamps with LED.   2) Selection of several common diodes   (1) detector diode  Generally, the detector diode is usually a point-contact type germanium diode. The detector with high working frequency, low reverse current, and large forward current should be selected according to the specific requirements of the circuit.   (2) rectifier diode Rectifier diodes are generally planar silicon diodes, used in various power rectifier circuits. When selecting rectifier diode, the parameters such as maximum rectified current, maximum reverse working current, cutoff frequency, and reverse recovery time should be considered. The rectifier diode used in the common series regulated power supply circuit is not strict with the reverse recovery time of cutoff frequency, so long as the maximum rectified current and the maximum reverse working current are selected according to the requirements of the circuit which can meet the requirements.   (3) Zener diode The Zener diode is generally used as a reference voltage source in a regulated power supply or as a protection diode in an overvoltage protection circuit. The selected Zener diode shall meet the main parameters based on the applying requirement. The stable voltage value of the Zener diode shall be the same as the reference voltage value of the application circuit, and the maximum stable current of the Zener diode shall be higher than the maximum load current of the application circuit by about 50%.   (4) switching diode  Switching diodes are mainly used in video recorders, TV sets, DVDs, and other household appliances and electronic equipment, such as switching circuits, detection circuits, high-frequency pulse rectifier circuits, and so on.   Medium-speed switching circuit and detection circuit, it is suitable to choose the 2AK series of ordinary switching diodes. High-speed switch circuits can choose RLS series, 1SS series, 1N series, and 2CK series high-speed switch diode.   According to the main parameters of the application circuit (such as forward current, maximum reverse voltage, reverse recovery time, etc.) to select the specific type of switch diode.   (5) variode When selecting variodes, the parameters such as working frequency, maximum reverse working voltage, maximum forward current, and zero-bias junction capacitance should be considered. A variode with a small reverse leakage current and various junction capacitance should be selected.     IV. Diode Types   There are many kinds of diodes. According to its semiconductor materials, it can be divided into germanium diodes (Ge-diodes) and silicon diodes (Si-diodes). According to its different applications, it can be divided into detector diode, rectifier diode, Zener diode, switching diode, isolation diode, Schottky diode, LED, silicon power-switch diode, rotary diode, and so on.    Semiconductor diodes work mainly on PN junctions. The point-contact type and Schottky type, which are the most common type based on the PN junction, and they also included in the range of general diodes. According to the characteristics of the PN structure(core structure), it can be divided into the point-contact diode, surface-contact diode, and planar diode.   1) point-contact type The point-contact diode is pressed on the surface of a clean semiconductor wafer with a thin metal wire, passing through a pulse current, so that one end of the contact wire is firmly sintered with the wafer to form a PN junction. Due to its point-contact characteristic, only a small current can flow through, thus it is suitable for high frequency and small current circuits, such as radio detection. However, compared with the surface junction type, the point-contact diode has poor forward and reverse characteristics, so it can not be used in high current and rectifier. Because the structure is simple, the price is cheap.   2) surface-contact type The PN junction of surface contact is made by alloy method or diffusion method. As for the surface-contact diode, its area of PN junction is larger, allowing a larger current to across through, it is suitable for the conversion of AC to DC circuit, that is rectifying function of diodes, but it is not suitable for the high-frequency circuit.   3) bond types  A bond diode is formed by melting gold or silver filaments on a single crystal sheet of silicon or germanium. and the characteristics are between the point-contact type diode and the alloy type diode. Compared with the point-contact type, although the PN junction capacitance of the bond diode is slightly increased, and its forward characteristic is particularly excellent. It is used as a switch and sometimes applied to the detection and power supply rectification (not greater than 50mA). In a bond diode, a diode of a fused gold wire is sometimes referred to as a gold bond type, and a diode of a fused silver wire is sometimes referred to as a silver bond type.   4) alloy type PN junctions were fabricated on N-type germanium or silicon single crystal wafers by adding indium, aluminum, and other metals. Small forward voltage drop, suitable for the large current rectifier. The PN junction is not suitable for high-frequency detection and high-frequency rectifier because of its large electrostatic capacity.   5) diffusion type In the high-temperature P-type impurity gas, the single crystal wafer heated with N-type germanium or silicon makes one part of the surface of the single crystal become P-type. Due to the small forward voltage drop of the PN junction, it is suitable for a high current rectifier. In addition, the use of high-current rectifiers has changed from silicon alloy to silicon diffusion.   6) mesa type Although its fabrication method of PN junction is the same as that of diffusion type, only the PN junction and its necessary parts are retained, and the unnecessary part is corroded by chemical. The rest of it takes on a mesa shape, hence its name. The initial production of this type is made of semiconductor materials by diffusion method. Therefore, this type is also called diffusion mesa. It usually used for small current switches.   7) planar type It is named after the surface of the semiconductor is made flat. In a semiconductor single crystal chip (mainly an N-type silicon single crystal chip), a P-type impurity is diffused, and a PN junction formed by selectively diffusing a part of the N-type silicon single crystal chip by a shielding effect of a silicon wafer surface oxide film. Therefore, it is not necessary to use chemicals. In addition, the surface of the PN junction is recognized as a type that having good stability and long service life due to the coating of the oxidized film. Initially, the semiconductor material used is formed by chemical extension, and the planar type is also referred to as an epitaxial planar type.    The planar diode is a kind of special silicon diode, it not only can pass through a large current, but also has stable and reliable performance, and it is widely used in switching, pulse, and high-frequency circuits.   8) alloy diffusion type It is a kind of alloy type. Alloy materials are easily diffused materials, which can be over diffused with the alloy by skillfully mixing impurities so that the proper concentration distribution of impurities can be obtained in the formed PN junctions. This method is suitable for the manufacture of high-sensitivity varactor diodes.   9) epitaxial type A diode formed by the manufacture of a PN junction by using an epitaxial surface length process. Manufacturing requires great skill. Because of its ability to control the distribution of impurities at random, it is suitable for the manufacture of high-sensitivity capacitive diodes.   10) Schottky   The basic principle is that: the formed substrate is used to block the reverse voltage on the contact-surfaces of metals (such as lead) and semiconductors (N-type silicon wafers). Schottky and PN junction have fundamental difference in the principle of rectifying function. Its voltage resistance is only about 40V. Its advantages are: switch speed is very fast: reverse recovery time is particularly short. Therefore, switching diodes and low-voltage high current rectifiers can be made based on this method.   According to application, diodes can be divided as :   1. detector diode  The main function of the detector is to detect the low-frequency signal in the high-frequency signal. It belongs to the point-contact type, so its junction capacitance is smaller and its working frequency is higher, and it is generally made of germanium. In principle, when the modulation signal is extracted from the input signal, usually, and the output current less than the 100mA( the rectifier current 100mA is used as the boundary) is called the demodulation. Its advantages include: the working frequency can reach 400MHz, the forward voltage drop is small, the junction capacitance is small, the detection efficiency is high, and the frequency characteristic is good. In addition to being used for detection, it can also be used for limiting, clipping, modulating, mixing, switching, and other circuits. Furthermore, there are also two diode assemblies dedicated to FM demodulation.   2. rectifier diode In principle, the output from the input AC DC is rectified. The rectified current size (100mA) is usually used as the boundary of the output current greater than the 100mA called a rectifier. Surface junction type, so junction capacitance is larger, generally below 3kHZ. Maximum reverse voltage from 25 volts to 3000 volts a total of 22 volts. Classified as follows: 1 silicon semiconductor rectifier diode 2CZ type, 2 silicon bridge rectifier QL type, 3 for television high voltage silicon stack working frequency near 100KHz 2CLG type.   3. clipper diode  The forward voltage drop of the diode is substantially unchanged after the diode is in conduction (the silicon tube is 0.7V, and the silicon tube is 0.3V). With this characteristic, the amplitude of the signal can be limited to a certain range with this limiting element in the circuit.   Most of the diodes can be used as a clipping component, but there is also a dedicated clipping diode like a protective instrument and a high-frequency Zanner diode. To have a particularly strong effect on limiting the sharp amplitude, a diode typically made of a silicon material. There is also a component set: a number of necessary rectifying diodes are connected in series to form a whole, depending on the need for limiting the voltage.   4. modulation diode It usually refers to the ring modulation dedicated diode. It is a combination of four diodes with good forward characteristics and consistency. Even though other varactor diodes have modulation applications, they are usually used directly as FM.   5. mixer diode  In the frequency range of 500~10000Hz, Schottky type and point-contact type diodes are usually used when diode mixing mode is used.   6. amplifier diode The amplification of a negative resistance device, such as a tunnel diode and a bulk diode, is generally performed with a diode, and also the parametric amplification of the variode. Thus, the amplification diodes generally refer to a tunnel diode, a bulk diode, and a variode.   7. switching diode The resistance of the diode is very small under the forward voltage, which is equivalent to that of an on-on switch; under the action of reverse voltage, the resistance is very large, and in the cut-off state, that is turn off state. All kinds of logic circuits can be formed by using the switching characteristics of diodes.   A logic operation with a small current and a magnetic core excitation switching diode for use in milliamperes. The small current switching diode is usually a point-contact type and a bond diode, and also has a silicon diffusion type, a mesa type, and a planar type diode which can work at high temperature. The advantage of the switching diode is that the switching speed is fast, and the switching time of the Schottky diode is very short, thus it is the ideal switching diode. The 2AK point-contact is used for medium-speed switch circuits; the 2CK-type plane is used for high-speed switching circuits, usually for switches, clipping, clamp bits, or detection circuits, and the Schottky-barrier diode has the advantages of small positive voltage drop, high speed, and high efficiency.   8. variode Low-power diode for automatic frequency control (AFC) and tuning. Other manufacturers also have many other terms. When applying reverse voltage, the electrostatic capacity of the PN junction will change. Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation, and tuning. Generally, although silicon diffusion diodes are used, special diodes such as alloy diffusion type, epitaxial bonding type, and dual diffusion type can be used, because the electrostatic capacity of these diodes has a very large change rate for voltage. Junction capacitance changes with reverse voltage and replaces variable capacitance, used in tuning circuit, oscillating circuit, phase-locked loop circuit. For example, it is often used in TV high-frequency channel conversion and tuning circuits and mostly made of silicon material.   9. frequency multiplication diode For the frequency multiplication of diodes, the frequency doubling depends on the frequency doubling of the variode and the frequency multiplication of the snap-off diode. The variode used for frequency multiplication is called a variable reactor. Although the variable reactor works the same principle as the variode used in automatic frequency control, the construction of the reactor can withstand high power. Snap-off diode, also called step recovery diode, has a short reverse recovery time when switch on to switch off. If sine waves are applied to snap-off diodes because the on-off time is short, so the output waveform is quickly cut off, it can produce a lot of high-frequency harmonics.   10. Zener diode   This type is based on the reverse breakdown characteristic to be made. The voltage at both ends of the circuit remains basically unchanged, which plays the role of stabilizing the voltage. It is made into a diffusion or alloy type of silicon. Its reverse breakdown characteristic curve changes sharply. Made as a control voltage and a standard voltage component. Diode terminal voltage (also known as Zener voltage) from about 3V to 150V, which can be divided into many grades. In terms of power, there is 200mW to 100W or more. Working in the reverse breakdown state, the dynamic resistance RZ is very small. The two complementary diodes are connected in reverse series to reduce the temperature coefficient, which is turned into a 2DW type.   The p-n junction of Zener diodes is highly doped. And normal diodes will also break down with a reverse voltage but the voltage and sharpness of it may not as well as defined. Also, normal diodes are not designed to operate in the breakdown region, but Zener diodes can reliably operate in this case.   Zener diodes are widely used in electronic devices(almost all kinds) and are one of the basic parts of electronic circuits. It is used to generate low-power stabilized supply rails from a higher voltage and to provide reference voltages for circuits, particularly stabilized power supplies. It is also used to protect circuits from overvoltage, especially electrostatic discharge.   11. PIN diode This is a crystal diode constructed by a layer of intrinsic semiconductors (or low concentration impurity semiconductors) between the P and N regions. When the operating frequency exceeds 100MHz, the diode becomes an impedance element due to the memory effect of minority carriers and the transit time effect in the "intrinsic" layer, it becomes an impedance element because of losing rectifying function, and its impedance value varies with the bias voltage. The impedance of the "intrinsic" region is very high when the bias is zero or the DC reverse bias, and the "intrinsic" region is low impedance due to the carrier injection into the "intrinsic" region when the DC is positive bias. Therefore The PIN diode can be used as a variable impedance element. It is often used in high-frequency switches (microwave switches), phase shift, modulation, amplitude limiting, and other circuits.   12. avalanche diode It is a transistor that can produce high-frequency oscillation under the behavior of applied voltage. The working principle of producing high-frequency oscillation is that the carrier is injected into the crystal by avalanche breakdown. Because the carrier transit chip takes a certain time, the current lags behind the voltage, and the delay time occurs. If the transit time is controlled properly, there will be a dynatron effect in the relationship between current and voltage, which will produce high-frequency oscillation. So it is often used in oscillating circuits in the microwave field.   13. tunnel diode It is a crystal diode based on tunneling effect current as of the main current component. The substrate materials are gallium arsenide and germanium, and the N-type region of the P region is highly doped.    A tunnel diode is a dual terminal active device, and it can be used in low-noise and high-frequency amplifiers and high-frequency oscillators (whose operating frequency can be up to millimeter-wave level) or in high-speed switching circuits.   (Note: Tunneling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier that it cannot surmount under the provision of classical mechanics.   Tunneling plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the Sun. It has important applications in the tunnel diode, quantum computing, and scanning tunneling microscope. The effect was predicted in the early 20th century, and its acceptance as a general physical phenomenon came mid-century.   Fundamental quantum mechanical concepts are central to this phenomenon, which makes quantum tunneling one of the novel implications of quantum mechanics. Quantum tunneling is projected to create physical limits to the size of the transistors used in microprocessors, due to electrons being able to tunnel past them if the transistors are too small.)   14. step recovery diode It is also a diode with a PN junction. Its structural characteristics are that there is a steep impurity distribution area at the boundary of the PN junction, thus forming a "self-help electric field". The reverse current of the PN junction can be reduced to the minimum value (reverse saturation current) after a "storage time" because of the charge storage effect in the vicinity of the PN junction due to the conduction of a few carriers at the forward bias voltage. The self-help electric field of the step recovery diode shortens the storage time, makes the reverse current cut off quickly, and produces abundant harmonic components. The comb spectrum generation circuit can be designed by using these harmonic components. Fast turn-off (step recovery) diodes are used in pulse and high-order harmonic circuits.   15. Schottky barrier diode It is a metal-semiconductor junction diode with Schottky characteristics. The forward starting voltage is lower. In addition to materials, gold, molybdenum, nickel, titanium and other materials can be used in the metal layer. Its semiconductor materials are silicon or gallium arsenide, mostly N-type semiconductors. This device is conductive by most carriers, so its reverse saturation current is much larger than that of PN junction with minority carrier conduction. Because the memory effect of minority carriers in Schottky diodes is very small, the frequency response of it is limited only by the RC time constant, so it is an ideal device for high frequency and fast switching. Its working frequency can reach 100GHz. And, MIS (metal-insulator-semiconductor) Schottky diodes can be used as solar cells or light-emitting diodes.   It also can be used as a continuation diode in the switching power supply inductance and plays a role in the continuation of the current in the relay and another inductive load.   16. damping diode  Damping diodes are widely used in high-frequency voltage circuits, with high reverse working voltage and peak current, but their forward voltage drop is small. It is a kind of high frequency and high voltage rectifier diodes, and often used in TV line scanning circuits for damping and boost rectifying. The commonly used damping diodes are 2CN1, 2CN2, BSBS44, and so on.   17. transient voltage suppressor(TVS) TVS is used to protect the circuits when having a fast overvoltage. They are divided into two types: bipolar and unipolar, classified by the values of peak power (500W-5000W) and voltage (8.2V~200V).   18. double-base diode (unijunction diode) A three-terminal negative resistive device with two base electrodes and emitter used in an oscillating circuit, has the advantages of easy frequency adjustment and good temperature stability.   19. LED It is made of gallium phosphide and gallium arsenide. Low working voltage, small operating current, uniform luminescence, long life, emitting red, yellow, green, blue monochromatic light. With the development of technology, white light and highlight diode to forming the new industry of LED lighting. It is also used in VCD, DVD, calculators, and other displays.   20. silicon power switching diode The silicon power switching diode has the capability of high-speed conduction and cut-off. It is mainly used for high-power switch or voltage-stabilizing circuit, DC converter, high-speed motor speed-regulating, and high-frequency rectification and free-wheeling, and has the advantages of soft recovery property and strong overload capacity. And it is widely applied to the computer, radar power supply, stepper motor speed-regulation, and so on.     According to characteristic, diodes can be divided as:   Point-contact diodes, classified by forward and reverse characteristic, are as follows:   1. Common point contact diode This kind of diode, is usually used in demodulation and rectifier circuits and is an intermediate product with forward and reverse characteristics, such as SD34, SD46, 1N34A, and so on.   2. High reverse voltage resistance point contact diode A kind of component with maximum peak reverse voltage and the maximum DC reverse voltage, which used in the detection and rectification of high voltage circuits, but this type of diode generally has poor or moderate forward characteristics. In point-contact type germanium diode, there are SD38, 1N38A, OA81, and so on.    3. High reverse resistance point-contact diode Forward voltage characteristics are the same as general diodes. Although its reverse voltage is also particularly high, the reverse current is small. Used in circuits with high input resistance and high resistance load. For example, SD54 and 1N54A belong to high reverse resistance diodes made of germanium material.   4. High conduction point-contact diode It is the opposite of the high reverse resistance type. Its reverse characteristics are poor, but the forward resistance is small. For high conduction point-contact diodes, there are SD56,1N56A and so on. For high conduction bond diodes, it has better properties when operating. When the load resistance is especially low, its rectifier efficiency is good.    V. Diode Conductive Property   The most important characteristic of diodes is unidirectional conductivity. In the circuit, the current can only flow from the positive, flow out from the negative.   1) forward characteristic    In electronic circuits, if the positive electrode of the diode is connected to the high potential terminal and the negative electrode to the low potential terminal, the diode will be switched on. This connection is called forward bias. It must be noted that when the forward voltage applied to both ends of the diode is very small, the diode cannot be switched on, and the forward current flowing through the diode is very weak.    2) reverse characteristic    In the electronic circuit, the positive electrode of the diode is connected to the low potential terminal, and the negative electrode is connected to the high potential terminal. In this case, there is almost no current flowing through the diode, and the diode is in the cut-off state. This connection mode is called reverse bias. When the diode is in reverse bias, there will still be a weak reverse current flowing through the diode, called leakage current. When the reverse voltage at both ends of the diode increases to a certain value, the reverse current will increase sharply, and the diode will lose the unidirectional conductivity, this state is called the breakdown of the diode as forward mentioned.   VI. Diode Parameters   The parameters of the diode are used for indicating the performance of the diode and the technical index of the applications. Different types of diodes have different characteristic parameters, and for beginners, the following main parameters must be understood:   (1) rated forward working current It refers to the maximum positive current allowed by the diode during long-term continuous operation.   (2) maximum surge current  It is an excess forward current that is allowed to flow. It is a transient current, and it is usually about 20 times the rated forward current.   (3) maximum reverse operating voltage When the reverse working voltage at both ends of the diode reaches a certain value, the tube will break down and lose its unidirectional conductivity. In order to keep safe, a maximum reverse working power value is specified. For example, the reverse voltage of an lN4001 diode with a reverse voltage of 50V, and is 1000V for IN4007.   (4) reverse current Reverse current is a kind of current that the diode flows through the diode at a specified temperature and maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube. The reverse current is closely related to the temperature, the reverse current increases twice when the temperature rises 10℃ at one time. In addition, silicon diode has better stability than germanium diode at high temperature.   (5) reverse recovery time When the forward voltage converts into the reverse voltage, the current can not stop at a short time, because it has a delay time, which is called reverse recovery time. It directly affects the switching speed of the diode.   (6) maximum power The maximum power is the voltage applied at both ends of the diode multiplied by the current.    (7) dynamic resistance The ratio of the voltage variation near the static operating point to the variation of the corresponding current in the diode characteristic curve.   (8) frequency characteristic Due to the existence of junction capacitance, when the frequency is up to a certain degree, the capacitance reactance is small enough to make the PN junction short-circuit, resulting in the diode loses unidirectional conductivity and cannot work. The larger the PN junction area is, the larger the junction capacitance is, so it can’t work at high frequency.   VII. Diode Testing   General diodes (including detection diodes, rectifier diodes, damped diodes, switching diodes, continuous diodes) have unidirectional conductivity. It is suitable to use a multimeter to detect the positive and reverse resistance, the electrode of the diode can be identified and the damage of the diode can be estimated.   1. The multimeter is placed in the R×100 barrier or R×1k barrier for polarity discrimination. The two-meter pens are connected with two electrodes of the diode respectively. After one result is measured, the two-meter pens are adjusted to obtain another result. In the two measurements, the large resistance value measured is reverse resistance, and the smaller resistance value measured is forward resistance. In addition, the black meter pen is connected with the positive pole of the diode, and the red meter pen is connected with the negative pole of the diode during a small resistance measurement.   2. In general, the positive resistance of GE diode is about 1kΩ and the reverse resistance is about 300. The resistance of the silicon diode is about 5kΩ and the reverse resistance is infinity. The smaller the forward resistance, the better the reverse resistance. The greater the difference between the positive and reverse resistance values, the better the unidirectional conductivity of the diode. If the positive and reverse resistance values of the diodes are all close to zero or the resistance values are small, the internal breakdown short circuit or leakage damage of the diode is indicated. If the positive and reverse resistance values of the diode are infinite, then the dipole is proved. The pipe is open and damaged.   3. Detection of reverse breakdown voltage(withstand voltage) of the diode can be measured by a transistor DC parameter meter. The method is: when measuring the diode, the "NPN/PNP" selection key of the testing meter should be set to the NPN state, and the negative pole should be inserted into the "e" jack of the testing meter and the positive pole of the diode should insert to the "c" jack, then press the V (BR) key, finally the reverse breakdown voltage of the diode can be detected. Another way is that a megohmmeter and a multimeter are used to measure the reverse breakdown voltage of the diode. When measured, the negative electrode of the diode is connected to the positive pole of the megohmmeter, and the positive electrode of the diode is connected to the negative pole of the megohmmeter, and meanwhile, the voltage across the diode is monitored by a multimeter (placed in the appropriate DC voltage level).    Several Detection methods of Common Diode   1. Detection of a low power crystal diode A. Distinguishing positive and negative electrode   (a) Observe the symbol mark on the shell. Usually, the symbol of the diode is marked on the shell with the one end with the triangular arrow being the positive and the other end is the negative pole.   (b) Observe the color dots on the shell. On the shell of a point-contact diode, it is usually marked with a polar color dot (white or red). One end with a general colored point is a positive pole. There are also diodes marked with color bands, and one end with the color bands is a negative pole. For example, a diode shell with a silver band is the negative pole.   (c) the one end of the black meter pen is the positive pole, and one end of the red meter pen is the negative pole, whichever takes the smaller value.   B. Detecting the maximum reverse breakdown voltage.    For alternating current, the maximum reverse operating voltage is the AC peak voltage the diode receives because it is constantly changing.   2. Detection bidirectional trigger diode Put the multimeter in the corresponding DC voltage block. When testing, shake the mega-meter to measure the VBR value. Finally, comparing VBO with VBR, the smaller the difference between the absolute values, the better the symmetry of the measured bidirectional trigger diode.   3. Detection of transient voltage suppression diode (TVS) The multimeter is used to measure the quality of the tube. According to the method of measuring the common diode, the positive and reverse resistance can be measured for the single-pole TVS. The general forward resistance is about 4kΩ, and the reverse resistance is infinity.   For the bidirectional polar TVS, the resistance between the two pins measured by two-meter pens should be infinite, otherwise, the diode performance is poor or damaged.   4. Detection of high-frequency variable-resistance diodes The difference between the positive and negative of high-frequency resistive diodes and ordinary diodes in appearance is that the color code is different. Ordinary diodes are generally black, while high-frequency resistive diodes are always a light color. Its polarity of the band is similar to that of the ordinary diode, that is, one end with a green band represents a negative pole, and the other end without a green band is a positive pole.   5. Detection of variode Inter-modulation by adjusting the red meter pen and the black meter pen of the multimeter, the resistance value between the two pins of the variode should be infinite. During the measurement, it is found that the multimeter pointer has a slight swing to the right or resistance of zero, indicating that the measured variode has a leakage fault or has broken down.   6. Detection of monochromatic light-emitting diodes A 1.5V dry battery is attached to the outside of the multimeter, and the multimeter is placed in R×10 or R×100 block. This method is equivalent to giving the multimeter a voltage of 1.5V, which increases the detection voltage to 3V (the starting voltage of the LED is 2V). When detecting, rotate the two pins of the LED with the two-meter pens of the multimeter. If the diode performance is good, there must be a normal luminous, at this time, the black pen is connected to the positive pole and the red pen is connected to the negative pole.   7. Detection of Infrared light-emitting diode A. Identify the positive and negative electrodes of infrared LEDs. An infrared LED has two pins, usually, the long pin is positive and the short pin is negative. Because the infrared LED is transparent, the electrode inside the tube and shell are clearly visible. The larger electrode is the negative electrode, and the narrower and smaller one is the positive electrode.   B.Measure the positive and reverse resistance of infrared LED firstly, usually, the forward resistance should be about 30k, reverse resistance should be more than 500k so that the device can be used normally.   8. Detection of IR receiver A. identify pin polarity   (a) Detection in appearance. The common IR receiver appearance color is black. When recognizing pins, facing the light window, from left to right, it is positive and negative respectively. In addition, there is a small oblique plane at the top of the IR receiver, usually a negative pin at one end with the oblique plane and a positive electrode at the other end.   (b) First uses multimeter to judge the positive and negative electrodes of common diodes, that is, to exchange red and black meter pen to measure the resistance between the two pins of the diode twice. Under normal conditions, the obtained resistance values should be various. Taking the smaller resistance, the connected end by the red-meter pen is negative and the black-meter pin is positive.   B. detection performance   The forward and reverse resistance of the IR receiver is measured by a multimeter electric barrier. According to the value of forward and reverse resistance, the quality of the IR receiver can be primarily judged.   9. Laser diode detection The pin arrangement order of the laser diode can be determined according to the method of detecting the forward and reverse resistance of ordinary diodes. However, it is important to note that since the forward voltage drop of the laser diode is larger than that of the ordinary diode, the multimeter pointer only slightly swings to the right when detecting the forward resistance.   FAQ   1. What is diode and its symbol? Diode, an electrical component that allows the flow of current in only one direction. In circuit diagrams, a diode is represented by a triangle with a line across one vertex.   2. What is special about a diode? Some semiconductor junctions, composed of special chemical combinations, emit radiant energy within the spectrum of visible light as the electrons change energy levels. Simply put, these junctions glow when forward biased. A diode intentionally designed to glow like a lamp is called a light-emitting diode, or LED.   3. Are diodes AC or DC? It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction. Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc). Diodes are rated according to their type, voltage, and current capacity.   4. Why do we use zener diode? Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.   5. What is unit of diode? A diode is not a measurable quantity. Hence,it does not have a unit. Generally,for a diode,we measure characteristics like forward voltage drop,reverse voltage drop and reverse breakdown voltage which are usually measured in Volts.   6. Do diodes have resistance? Just like a resistor or any other load in a circuit, a diode offers resistance in a circuit. Unlike resistors, though, diodes are not linear devices. This means that the resistance of diodes does not vary directly and proportional to the amount of voltage and current applied to them.   7. Does diode reduce current? Ideally, diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward. Unfortunately, actual diode behavior isn't quite ideal. Diodes do consume some amount of power when conducting forward current, and they won't block out all reverse current.   8. How are diodes classified? Diodes are classified according to their characteristics and are offered in a number of different types, including rectifiers, switching diodes, Schottky barrier diodes, Zener (constant voltage) diodes, and diodes designed for high-frequency applications.   9. What is the most common diode? The most commonly used signal diode is the 1N4148. This diode has a close brother called 1N914 that can be used in its place if you can't find a 1N4148. This diode has a forward-voltage drop of 0.7 and a peak inverse voltage of 100 V, and can carry a maximum of 200 mA of current.   10. What is the difference between a Zener diode and a Schottky diode? As their switching speed is very high, Schottky diodes recover very fast when the current reverses, resulting in only a very small reverse current overshoot. ... A special type of diode, called the Zener diode, blocks the current through it up to a certain voltage when reverse biased.   11. What is difference between Schottky diode and normal diode? In the normal rectifier grade PN junction diode, the junction is formed between P type semiconductor to N type semiconductor. Whereas in Schottky diode the junction is in between N type semiconductor to Metal plate. The schottky barrier diode has electrons as majority carriers on both sides of the junction.   12. Why it is called diode? A diode is called a diode because it has two distinct electrodes (i.e. terminals), called the anode and the cathode. A diode is electrically asymmetric because current can flow freely from the anode to the cathode, but not in the other direction. In this way, it functions as a one-way valve for current.   13. Is a diode the same as a resistor? Key Difference: A diode is a type of electrical device that allows the current to move through it in only one direction. ... A resistor is an electric component that is used to provide resistance to current in the circuit. They are mostly used to produce heat or light.   14. How much voltage can a diode take? Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.   15. Can a resistor replace a diode? Diodes only conduct in one direction whereas resistors conduct in both directions. Without analyzing the actual circuit the results would be unpredictable but, generally speaking, being that diodes & resistors are designed to do different things, substituting one for the other is something you wouldn't want to do.   You May Also Like Characteristics and Functions of Diodes Rectifiers and Filters Notes Simplify Current Monitoring by Using Diode | Power Supply Negative End