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Many engineers who have not used the switching power supply may have some worry about it, such as the PCB layout, the parameter and type selection of components, and so on. In fact, as long as you understand the basic principle, the use of switching power supply design is very convenient. In today's article, we will introduce you to some basic knowledge of switch-mode power supply, along with some experience sharing when using the switch-mode power supply. SMPS Tutorial: Switch Mode Power Supplies and Power Conversion  Catalog I. What is the Switch Mode Power SupplyII. How to Debug the Switching Power Supply Circuit?III. What Needs to Be Grounded?3.1 Definition of Grounding3.2 Grounding Mode3.3 How is the Signal of the Single Board Grounded?3.4 How Do the Single Board Interface Devices   Grounding?3.5 How to Grounding the Shield Layer?IV. Introduction of Signal Backflow and TranspartitionV. Should Analog Separate from the Digital , and How?FAQ I. What is the Switch Mode Power Supply  A switch-mode power supply usually consists of a controller and an output part. Some controllers integrate MOSFET into the chip, which makes it easier to use and simplify the PCB design, but the flexibility of components is weakened. The switching controller is actually a closed-loop feedback control system, so there is a sampling circuit of output-voltage feedback and a feedback-loop control circuit. Therefore, this part of the design is to ensure an accurate sampling circuit and to control the feedback depth, because if the feedback loop response is too slow, it will have a great impact on the transient response-ability. The output parts include output capacitance, output inductor, MOSFET, and so on. The selection of these devices is basically to balance the performance need and cost. For example, the high switching frequency can use small inductance (which means small package and low cost), but a high switching frequency will increase interference and the switching loss of MOSFET, result in reducing efficiency and increasing cost. Lower switching frequency has the opposite effect. The selection of Rds_on parameters of MOSFET and the ESR for output capacitance is also very important. ESR is small can reduce output ripple, but the cost of the capacitor will increase. And It is important to note that switching power controllers can not be well driven with too much MOSFET. In general, suppliers of switching power supply controllers will provide specific formulas and usage options for engineers. Figure. 1 Switch Mode Power Supply Circuit   II. How to Debug the Switching Power Supply Circuit? （1）The output of the power supply circuit is installed to the board through the low resistance and high power resistor, so that the power circuit can be debugged first before welding resistance, avoiding the influence of the latter circuit.  （2）The switching controller is a closed-loop system. If the output deterioration beyond the range that the closed-loop can control, the switching power supply will work improperly. This situation requires careful examination of feedback and sampling circuits. Especially, if the output capacitance with a large ESR, lots of ripple of power supply will be produced, which will also affect the operation of switching power supply.  III. What Needs to Be Grounded? At the very start, the introduction of grounding technology is a protective measure to prevent lightning strikes on electric power or electronic equipment. The purpose is to introduce lightning current through the lightning rod to the earth to protect buildings. And meanwhile, grounding is also an effective way to protect personal safety.  When the phase line touches the shell of the equipment causing by some reason (such as poor insulation of the wire, line aging, etc.), there will be a dangerous voltage in the shell of the equipment. Having grounding, the resulting fault current will flow to the earth, thus it plays a protective role.  For example, in communication systems, the interconnection of signals between a large number of devices requires each device to have a point as a reference, and with the complication of electronic equipment, the signal frequency is becoming higher and higher, therefore, grounding design as special attention paid to the electromagnetic compatibility problems such as mutual interference between signals.  In addition, improper grounding will seriously affect the reliability and stability of system operation. Recently, the concept of "grounding" has also been introduced into high-speed signal backflow technology.  3.1  Definition of GroundingIn the modern concept of grounding, for line engineers, the term usually means "reference point for line voltage"; for system designers, it is often a cabinet or frame; for electrical engineers, it is a green and safe ground line or a wire connected to the earth. A more general definition is that "grounding is the low impedance channel which the current returns its source." Noting that the points are "low impedance" and "channel".  3.2  Grounding ModeThere are many ways of grounding: single-point grounding, multi-point grounding, and mixed type of grounding. Single-point grounding is divided into a series of single-point grounding and parallel single-point grounding. In general, single-point grounding is used in simple circuits, and low frequency (f10MHz) circuits use multipoint grounding or multilayer (complete a ground plane layer).  3.3   How is the Signal of the Single Board Grounded?For the general device, the near ground is the best. After adopting the multilayer design with a complete ground plane, the grounding of the general signal is very easy. The basic principle is to ensure the continuity of the line, reduce the number of holes, approach the ground plane or the power plane, etc. 3.4  How Do the Single Board Interface Devices  Grounding?Some veneers will have external input-output interfaces, such as serial port connectors, RJ45 connectors, etc. If their grounding is not well designed, it will also affect normal operation, such as error codes, packet loss, etc. And it will become an external source of electromagnetic interference sending the noise out. In general, a single interface grounding will be made, and the signal is connected by a thin wire connection, string 0 ohms, or small resistance. Thin lines can be used to block signal ground noise. At the same time, the interface and the interface power filter should also be considered seriously.  3.5  How to Grounding the Shield Layer? The shielding layer of cables is connected to the interface grounding instead of the signal grounding, because there are various noises on the signal grounding. If the shield layer is connected to the signal ground, the noise voltage will drive the common-mode current to interfere outward along the shield layer. Therefore, the poorly designed cable is generally the maximum noise output source of electromagnetic interference. Of course, the interface ground should keep clean. IV. Introduction of Signal Backflow and TranspartitionFor an electronic signal, it needs to find a way with the lowest impedance to return current to the ground, so how to deal with the signal backflow becomes very important. First, according to the formula, we can know that the radiation intensity is proportional to the area of the loop. Specifically, the longer the path the return is, the bigger the ring is formed, and the greater the external radiation interference is, thus the power-circuit flow back and signal loop area should as small as possible when design PCB. Second, for a high-speed signal, providing a good signal backflow can guarantee its signal quality. Because the characteristic impedance of the transmission line on the PCB is generally calculated by reference to the ground (or power layer), if there is a continuous ground plane near the high-speed line, the impedance of this line can be kept continuous, and if there is no ground reference near the section line, the impedance will change and the signal will be affected as well. Therefore, the high-speed lines should be distributed to the layer near the ground plane, or they should be walked in parallel next to each other, to shield interference and provide backflow nearly.  Third, do not divide wires when having power supply in wiring way, this is because the signal backflow path across different power layers will be longer, and be vulnerable to interference. For low-speed signals, it is not strictly required that, because the resulting interference signal can not be concerned about. But for high-speed signals should be checked carefully, do not cross as far as possible, you can adjust the power part of the wire. (this is for multiple power supplies on multilayer boards).  V. Should Analog Separate from the Digital , and How? Whether analog signal or digital signal should return to the ground. Because the digital signal changes quickly and the noise caused by the digital signal will be very large, if analog and digital mixing, the noise will affect the analog signal.  In general, the grounding of analog and digital processing must be separated, then connected by a thin line, or a single point. The general idea is to try to block the noise from the digital ground to the analog ground. But it is not a very strict requirement that analog and digital ground must be separated, if the analog section near the digital ground is still very clean, they can be combined. FAQ 1. What are the 3 types of power supply?There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages. 2. What is meant by switch mode power supply?A switch mode power supply is a power converter that utilises switching devices such as MOSFETs that continuously turn on and off at high frequency; and energy storage devices such as the capacitors and inductors to supply power during the non-conduction state of the switching device. 3.What are the advantages and disadvantages of switch mode power supply?Advantages & disadvantages of switch mode power supply (SMPS)a. The switch mode power supply has a smaller in size.b. The SMPS has light weight.c. It has a better power efficiency typically 60 to 70 percent.d. It has a strong anti interference.e. SMPS has wide output range.f. Low heat generation in SMPS. 4. What is a DC switching power supply?A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor. 5. What is the difference between a switching power supply and a linear power supply?Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges. 6. Do I need a switching power supply?The switching power supply implies higher efficiency due to the high switching frequency, enabling it to use a smaller, less-costly high-frequency transformer as well as lighter, less-costly filter components. Switching power supplies contain more overall components, therefore are usually more expensive. 7. Is a switching power supply regulated?A switch mode power supply regulates an output voltage with pulse width modulation (PWM). This process creates high-frequency noise but it provides a high-efficiency rating in a small form factor. ... The low DC voltage is finally converted into a steady DC output with another set of diodes, capacitors, and inductors. 8. How do I know if my power supply is regulated?You can generally stick one probe into the middle of the connector, and hold the other against the outside. With a few exceptions, the middle is positive, so use the red lead there, and use the black lead on the outside shell. Regulated supplies, without any load, should measure very close to the target voltage of 12v. 9. Can I use a switching power supply to drive a DC motor?A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC. 10. Are switch mode power supplies any good?Switch mode power supplies, SMPS provide improved efficiency & space saving over traditional linear supplies, but care has to be taken to ensure noise on the output is low. Switch mode power supplies are widely used because of the advantages they offer in terms of size, weight, cost, efficiency and overall performance. You May Also LikeSwitching Power Supply Guide: Protection CircuitSwitching Power Supply Tutorial: 4V～16VSwitched Mode Power Supply Tutorial: Principles & Functions of SMPS Circuits

With the development of science and technology, electronic products are changing with each passing day. Also, electronic assembly technology is facing challenges. Following the development of electronic technology, people work harder to make innovations in electronic assembly technology.  And in this context, a flexible circuit board invented used which made of the thin-and-flexible polymer film. It can complete the application of surface mounting technology and bend without affecting the normal circuit operation.  Clear Flexible Printed Circuit Catalog I. Brief IntroductionII. Five Main Materials for Flexible Circuit Board2.1 Insulating Firm2.2 Bonding Sheet2.3 Copper Foil2.4 Overburden2.5 Reinforcement PlateFAQ I. Brief Introduction Today's flexible electrons are all made of SMT technology, so they are thin and exquisite with insulation thickness of fewer than 25 μm. It can be bent arbitrarily and rolled into a cylinder. And it makes full use of three-dimensional volume. It breaks the stereotype of the traditional area of use and creates the ability to make full use of the shape of the volume, which can significantly enhance the effective density of use in the length of the conductor currently routinely used per unit area, forming a high-density assembly. In recent years, flexible circuit technology has been applied in various fields, such as radio communication, computer, and automobile electronic equipment. Unlike in the past, flexible circuits have been used as substitutes for rigid cables, and they have been used as substitutes for rigid circuits and printed circuit boards (PCB) in applications where thin or three-dimensional circuits are required. In order to meet the requirements of rigid and flexible applications, it is combined flexible circuit technology in the rigid circuit board, making flexible circuit board used widely. The functions of the flexible circuit board can be divided into four categories, including the lead line, printed circuit, connector, and IntegraTIon of FuncTIon, which covers the computer, Computer peripheral auxiliary system, civil electrical appliances and cars, and other areas. For different applications, the material of the flexible circuit board should select carefully. And the followings are some rules of the five main materials of the flexible circuit board.  II. Five Main Materials for Flexible Circuit Board 2.1 Insulating FirmThe insulating film is flexible and can be used as the insulation carrier of the circuit board to form the basic layer of the circuit. When selecting the flexible dielectric film, the heat resistance, overlay, thickness, mechanical properties and electrical properties of the material should be tested.  Insulation film is usually available on the market, the most common is polyimide and polyester materials. Of all the flexible circuit manufacturers in the United States, nearly 80% use polyimide film as the material for flexible circuits, and about 20% use polyester film. Because polyimide material is nonflammable, stable geometry, high anti-tear, and able to withstand high temperature during welding. 2.2 Bonding Sheet It is made up of two insulating films coated with adhesive, the ability is gluing the film to the foil, and the film to the film in the flexible circuit, In order to provide mechanical support and eliminate stress during insertion of components and connectors. It also can provide protection and electrical insulation. Different types of adhesive sheets can be used for different film substrates, such as polyester bonding sheets and polyimide bonding sheets are different, for example, the polyimide substrate has epoxy resin and acrylic acid. 2.3 Copper FoilCopper foil is a conductor layer that is coated on the insulating substrate and then selectively etched to form a conductive line. The vast majority of this copper foil is rolled copper foil or electrolytic copper foil. The ductility and bending resistance of the rolled copper foil is better than that of the electrolytic copper foil.  The elongation of the rolled copper foil is 20%~45% and the electrolytic copper foil is 4%~40%. The commonly used thickness of copper foil is 35um (1oz), also they have 18um (O.5oz), 70um (2oz), or even 105um (30z). According to different applications, we have to choose different forms of copper foil.  If only to replace wires and connectors, and to reduce manufacturing time and cost, the best choice is electrolytic copper foil. The electrolytic copper foil will increase the weight of copper to level the load capacity of the current, thus obtaining the suitable width of the copper sheet. 2.4 OverburdenThe brand, Novaclad, created by Sheldahl, applies the vacuum metal spraying technology which is a patent. It is a technology that applying a thin layer of pure copper to the surface of a polyimide film, then electroplating into a specific thickness to form the substrate of Novaclad. The base material is used in Novaflex, a flexible circuit without adhesive. After all the circuits have been made, a layer of Novaflex insulation is applied. The Novaflex is designed to work under harsh conditions, and Novaflex without adhesive provides better flexibility, chemical resistance, high-temperature properties, and maximum heat dissipation properties. 2.5 Reinforcement PlateThe reinforced plate to the local position of the flexible plate plays the role of super supporting and strengthening the flexible film substrate, which is convenient for the connection, fixation, or other functions of the PCB. According to different needs, the reinforcement board materials commonly use polyester, polyimide sheet, epoxy fiberglass cloth plate, phenolic-aldehyde paper board, steel plate, aluminum plate, etc.  FAQ 1.What is a flexible circuit board?A flexible printed circuit board features a combination of several printed circuits as well as components that are positioned on a flexible substrate. These circuit boards are also known as flex circuit boards, flex PCBs, flex circuits, or flexible printed circuits. 2. What is flex circuit used for?Flex circuits are often used as connectors in various applications where flexibility, space savings, or production constraints limit the serviceability of rigid circuit boards or hand wiring. A common application of flex circuits is in computer keyboards; most keyboards use flex circuits for the switch matrix. 3. What are flexible circuit boards made of?Flexible circuits are thin, light-weight electrical circuits that conform to small spaces and contoured shapes. They consist of conductive strips of metal, usually copper, encapsulated with an insulating dielectric material made of polyimide or a solder mask. 4. Where are flexible PCBS used?a. Automobiles.b. Consumer electronics including smartphones, SLR cameras and camcorders,c. Medical systems and devices such as heart monitors, pacemakers and the bionic knee.d. Motion systems.e. GPS systems.f. Aerospace and avionics systems. 5. When was the first flex printed circuit made?From early applications during World War II to the present, growth and proliferation for flex circuits and flexible printed circuit boards continues exponentially. A flexible circuit in its purest form is a vast array of conductors bonded to a thin dielectric film. 6. What are the advantages and disadvantages of flexible circuit boards?The advantages of the flexible circuit board are mainly high assembly density, which can save the connection of redundant cables, in addition, it has good bendability, high flexibility, small size, simple structure, and convenient installation.Disadvantages of flexible circuit boards: 1. High initial cost 2. Difficult to change and repair 3. Size limited 4. Improper operation and easy damage, etc. 7. What do flexible circuit boards and rigid circuit boards mean?a.  Flexible circuit boards are used more in digital products. The difference between it and the rigid circuit board is that the substrate of the circuit board is different. As the name implies, the board can be bent and softer.b. "Multilayer board" and "double-sided board" mainly refer to the number of sides of wiring on the circuit board. Above 2 layers are multi-layer boards.From the perspective of the process flow, the multilayer board needs to be processed by the inner layer map, and the outer layer can be processed after being pressed. The processing flow of the outer layer is basically the same as the processing flow of the double-sided board. 8. What is the temperature resistance of fpc flexible circuit boards?FPC flexible circuit board can withstand high temperature of 280 degrees, about 1 hour. However, the recommended temperature for normal use is not less than -20 and not higher than 80. 9. With flexible circuit boards, why pcb hard printed circuit boards are still not eliminated?For PCBs that need to use plug-in components, only rigid boards can be used, which is what you call rigid boards; for many PCBs with stress requirements, only rigid boards can be used. The cost of flexible boards is currently much higher than rigid boards, more than doubled. And the straight-through rate of rigid boards is higher than that of flexible boards 10.Classification of flexible circuit boards?According to the combination of base material and copper foil, flexible circuit boards can be divided into two types: flexible boards with glue and flexible boards without glue. Among them, the price of the glueless flexible board is much higher than that of the glued flexible board, but its flexibility, the bonding force of the copper foil and the substrate, and the flatness of the pad are also better than the glued flexible board. You May Also LikeSwitching Power Supply Tutorial: 4V～16VWhat is A MCU’s internal Structure: Single Chip Micro-ComputerPCB Wring Tutorial: A/D converterMonitoring Technology in Communication Power Supply: Application GuideDIY CommunityDIY Flxible Printed CircuitsMake Flexible Circuit Boards Using A 3D Printer

    Circuit protection is a frequently discussed topic, and the various types of circuit protection differ due to the various problems in the circuit. Short-circuit, overload, grounding, and lightning strikes are the most common faults in power supply systems. To ensure the safe and dependable operation of the power supply system, protection devices must be installed to monitor the working conditions of the power supply system, detect faults in time, and cut off the power supply of the faulty equipment, preventing the accident from spreading. In general, the protection circuit is made up of various relays, signal indicating devices, and other components. This blog provides an in-depth discussion on several circuit protections. Below is an introduction video about short circuit protection. DIY Short Circuit (Overcurrent) Protection   Catalog   I Introduction to circuit protection II Switching power principle and characteristics      2.1 Operational principle of switching power      2.2 Characteristic of switching power III DC Switching power supply protection      3.1 Overcurrent protection circuit      3.2 Overvoltage protection circuit      3.3 Soft start protection circuit        3.4 Overheat protection circuit IV Conclusion FAQ   I Introdcution to circuit protection The operation of electronic equipment can not be separated from electricity, so DC switching power supply which can control the electricity is playing a more and more important role. And it has entered various fields of electronics and electrical equipment: SPC exchange, communication, electronic testing equipment power supply and controlling equipment power supply, which are widely used DC switching power supply.  Meanwhile, with the development of many high-tech technologies, including high-frequency switching technology, soft-switching technology, power factor correction technology, synchronous rectifier technology, intelligent technology, surface installation technology, etc., switching power supply technology is constantly innovating. This provides a wide range of development for DC switching power supply.  DC current diagram   But the circuit is complex to control in the switching power supply, the transistor and the integrated device have poor resistance to electricity and thermal shock, which brings great inconvenience to the user in the process of using. In order to protect the safety of switching power supply itself and load, the overheat protection, over-current protection, over-voltage protection and soft start protection circuit are designed according to the principle and characteristics of DC switching power supply.   II Switching power principle and characteristics 2.1 Operational principle of switching power DC switching power supply is composed of input part, power conversion part, output part and control part. The power conversion part is the core of the switching power supply. It performs conversion which needed for the output on the high-frequency and unstable DC. It is mainly composed of switching transistor and high frequency transformer. Figure 1. DC Switching power supply principle Figure 1 shows the schematic diagram and equivalent schematic block diagram of DC switching power supply, which is composed of full wave rectifier, switching tube V, excitation signal, fly-wheel diode Vp, energy storage inductance and filter capacitance C. In fact, the core part of DC switching power supply is a DC transformer. 2.2 Characteristic of switching power   In order to meet the needs of users, the world's major switching power supply manufacturers are committed to the simultaneous development of new and highly intelligent components, especially by reducing the loss of the secondary rectifier. In order to improve the magnetic properties under high frequency and high magnetic flux density, power ferrite (Mn-Zn) materials have been developed. At the same time, the application of SMT technology in the field of switching power supplies has also made considerable progress. The components are arranged on both sides of the circuit board to ensure that the switching power supply is light, small and thin. Therefore, high frequency, high reliability, low power consumption, low noise, anti-interference and modularization are the development trends of DC switching power supplies. However, DC switching power supplies also have disadvantages. The DC switching power supply switch has serious interference, and its ability to adapt to harsh environments and sudden failures is weak. There is still a certain gap in microelectronics technology in developing countries. Specifically, the production technology of resistors and capacitors and the technology of magnetic materials are compared with those of some technologically advanced countries. Therefore, the manufacture of DC switching power supplies is very difficult. In most parts of the world, maintenance is difficult and the cost is high. III DC Switching power supply protection Based on the characteristics of DC switching power supply and the actual electrical condition, in order to make DC switching power supply work safely and reliably in bad environment and sudden fault, this paper designs a variety of protection circuits according to different conditions. 3.1 Overcurrent protection circuit   Figure 2. Input Overcurrent protection circuit In DC switching power supply circuit, in order to avoid short circuit and overflow damage to protect the regulator tube in the circuit, the basic method is that, when the output current exceeds a certain value, the regulator tube is in the reverse bias state, thus the circuit current is cut off automatically. As shown in Fig. 2, the over-current protection circuit consists of transistor BG2 and divider resistor R4, R5. When the circuit works normally, the base potential of BG2 is lower than that of emitter through the partial voltage interaction between R4 and R5, and the emitter junction bears reverse voltage. So the BG2 is in the cutoff state (equivalent to open circuit), which is used to stabilize the voltage. But the voltage stabilizing circuit has no effect. When the circuit is short circuit, the output voltage is zero and the emitter of BG2 is equivalent to grounding, then the BG2 is in the state of saturation conduction (equivalent to short circuit), so that the regulator tube BG1 base and emitter are close to short circuit, and in the cut-off state, the circuit current is cut off to achieve the purpose of protection.   3.2 Overvoltage protection circuit The overvoltage protection of switching regulator in DC switching power supply includes input overvoltage protection and output overvoltage protection. If the voltage of the unstabilized DC power supply (such as batteries and rectifiers) used by the switching regulator is too high, it will cause the switching regulator to fail to work properly and even damage the internal devices. Therefore, it is necessary to use the input overvoltage protection circuit in the switching power supply. Fig. 3 is a protection circuit composed of transistors and relays, in which the voltage of the input DC power supply is higher than the breakdown voltage of the zener diode, at this condition, current flows through resistor R, making diode T conducts. Following these electrical actions, relay operates and common closed contact disconnected, inputting current. The polarity protection circuit of the input power supply can be combined with the input overvoltage protection to form the polarity protection identification and overvoltage protection circuit. Figure 3. Input overvoltage protection circuit 3.3 Soft start protection circuit The circuit of switching power supply is complex, the input end of switching regulator is usually connected with small inductance and large-capacitance input filter. At start-up instant, the filter capacitor flows through a large surge current that can be several times the normal input current. Such a large surge current melts the contacts of the normal power switch or the relay and melts the input fuse. In addition, surge current can also damage capacitors, shorten their life, cause premature damage. To this end, a current-limiting resistance should be connected in the circuit, through this current-limiting resistance to charge the capacitor. In order not to consume too much power by the current limiting resistance, and avoid affecting the normal operation of the switching regulator, therefore a relay is used to connect it automatically after the transient process is finished, which makes the DC power supply directly to the switching regulator. This is called the "soft start" circuit of DC switching power supply. Figure 4. Soft start-up protection circuit When the power supply is switched on, capacitor C is charged by input voltage through rectifier bridge (D1 ~ D4) and current-limiting resistance R1 to limit the surge current. The inverter works normally when the capacitor C is charged to about 80% rated voltage. The trigger signal of thyristor is generated by auxiliary winding of main transformer, which makes thyristor switch on and short circuit current-limiting resistance R1, and the switching power supply is in normal operation state. In order to improve the accuracy of the delay time and prevent the relay operation from shaking and oscillating. The delay circuit can replace the RC delay circuit by the circuit shown in figure 4(b). 3.4 Overheat protection circuit The high integration and light weight of switching regulator in DC switching power supply greatly increase the power density per unit volume, so if the internal components of the power supply do not have a corresponding increase in the temperature of its working environment, it will inevitably make the circuit performance damaged and components life service shortened prematurely. Therefore, overheating protection circuit should be installed in high power DC switching power supply. Figure 5. Overtemperature protection circuit In this paper, the temperature relay is used to detect the internal temperature of the power supply device. When the inside of the power supply device is overheated, the temperature relay operates, which makes the alarm circuit of the whole machine in the state of alarm and realizes the protection of the overheating of the power supply.  As shown in Fig. 5 (a), the P type control gate thermal thyristor is placed near the power switch transistor in the protection circuit. According to the characteristics of the TT102 (the on-on temperature of the device is determined by the Rr value, the larger the Rr is, The lower the conduction temperature), when the temperature of the power tube or the temperature inside the device exceeds the allowable value, the thermal thyristor is switched on and the LED is lighting to give an alarm. If cooperate with photoelectric coupler which can make whole machine alarm circuit operation, protecting switch power supply.  The circuit can also be designed as shown in Fig. 5 (b) to protect the power transistor from overheating. The base current of the switching transister is bypassed by the TT201 of the N type control gate thermal thyristor, and the switch tube is cut off, also the collector current is cut off, and the overheating is prevented. IV Conclusion This blog mainly discusses various protection methods of internal devices in DC switching power supply, and introduces some concrete circuits. For a given DC switching power supply, it is very important for the security and reliability of the power supply device whether the protection circuit is perfect and set up to work necessarily. Because the protection scheme and circuit structure of switching power supply are diverse, reasonable protection scheme and circuit structure should be chosen for specific power supply devices. In practical application, several protection methods are usually used to form a perfect protection system to ensure the normal operation of DC switching power supply.   FAQ   1. What is the purpose of circuit protection? The basic goals of circuit protection are to 1) localize and isolate the condition or fault and 2) prevent and minimize any unnecessary power loss. There are several types of abnormal conditions that may occur throughout a building's life, in which an electrical system must be designed to correct or overcome.   2. What protective devices are used in circuits? Fuses, MCBs, RCDs, and RCBOs are all devices used to protect users and equipment from fault conditions in an electrical circuit by isolating the electrical supply.   3. How do you protect a circuit design? The most basic device is a fuse, a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. A fuse protects the circuit, but once it's utilized, it's kaput.   4. What are the two main circuit protection devices? The two types of circuit protection devices discussed in this chapter are fuses and circuit breakers. A fuse is the simplest circuit protection device. It derives its name from the Latin word "fusus," meaning "to melt." Fuses have been used almost from the beginning of the use of electricity.   5. What is a DC switching power supply? A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor.   6. What are the differences between linear DC power supply and switching power supply? Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges.   7. Can I use a switching power supply to drive a DC motor? A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC.   8. Do I need a switching power supply? The switching power supply implies higher efficiency due to the high switching frequency, enabling it to use a smaller, less-costly high-frequency transformer as well as lighter, less-costly filter components. Switching power supplies contain more overall components, therefore are usually more expensive.   9. What are the 3 types of power supply? There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.   10. What is a switching mode power supply used for? Switched-mode power supplies are used to power a wide variety of equipment such as computers, sensitive electronics, battery-operated devices and other equipment requiring high efficiency.    

In the design of circuit systems, we often encounter things like this: when a circuit program is copied from the book completely, the result of the experiment is not correct. Why is it that? The reason is interference. We must do a good job of anti-interference in the process of the electronic circuit and program design.     Catalog I. Three Basic Element of Interference II. Suppressing Interference Sources     2.1 Common Measures to Suppress Interference Sources     2.2 Common Measures to Cut off the Path of Interference Propagation     2.3 Improve the Anti-interference Performance of Sensitive Devices III. Experience and Advice FAQ   I. Three Basic Element of Interference   a. Interference Source: Refers to the components, devices, or signals that cause interference, as described in mathematical terms as follows: some places where the figure of du/dt(voltage regulator factor) or di/dt(current rate of charge) is large may be the interference source. Also the lightning, relays, SCR, motor, high-frequency clock and so on may become interference sources.   b. Propagation Path: Refers to A path or medium in which interference travels from an interference source to a sensitive device. The typical path of interference propagation is the conduction of wires and the radiation of space.    c. Sensitive Device: Refers to an object that is susceptible to interference. Such as A/D or D/A converter, single-chip microcomputer, digital IC, weak signal, and so on. The basic principle of anti-jamming design is to suppress the interference source, cut off the path of interference propagation, and improve the anti-jamming performance of sensitive devices.   II. Suppressing Interference Sources   Suppressing interference sources is to minimize the du/dt and di/dt of interference sources as much as possible. Reduce the du/dt of the interference source by paralleling capacitors at both ends of the interference source; reduce the di/dt of the interference source by using the series inductance or resistance in the interference source loop and adding the freewheel diode. This is the highest priority and the most important principle in anti-interference design.   2.1 Common Measures to Suppress Interference Sources are as follows: (1) Add freewheel diode to the relay coil to eliminate the interference when disconnecting the coil. Only having a freewheel diode will delay the break time of the relay, therefore adding an extra more Zener diode will increase the number of operating times of the relay in unit time.   (2) Connect spark suppression circuit at both ends of relay contact(is usually RC; resistor is selected from several kΩ to dozens of kΩ; capacitance selects 0.01uF), so as to reduce the interference.   (3) Add filter circuit to the motor, pay attention to the capacitance, and inductance lead should be as short as possible.   (4) each IC on the circuit board should be connected with a high-frequency capacitor of 0.01 μ F to 0.1 μ F to reduce the influence of IC to the power supply. Pay attention to the wiring of high-frequency capacitance. The connection should be close to the power supply and should be as short as possible. Otherwise, it will increase the equivalent series resistance of the capacitance, which will affect the filtering effect.   (5) Avoid 90 degree fold line and reduce high-frequency noise when wiring.   (6) Connect the RC suppression circuit to both ends of the thyristor to reduce the noise caused by the thyristor (ps: if the noise is serious may break down the thyristor).   According to the path of interference, it can be divided into two types: conduction interference and radiation interference. Conduction interference is the interference that propagates through the wire to the sensitive device. The high-frequency interference noise is different from the useful signal in the frequency band, which can be cut off by adding a filter to the conductor, and sometimes it can be solved by isolating the optical coupling. Power noise is the most harmful, we should pay special attention to handling. Radiation interference refers to the interference which propagates through the space radiation to the sensitive device. The general solution is to increase the distance between the interference sources and the sensitive devices, to isolate them with grounding wires, and mask the sensitive devices.     2.2 Common Measures to Cut off the Path of Interference Propagation (1) Consider the influence of power supply on single-chip computers. A good power supply helps solve the majority of the jamming problems in circuit design. Many single-chip computers are sensitive to the noise of the power supply, so it is necessary to add a filter circuit or voltage stabilizer to the power supply of a single-chip microcomputer to reduce the interference. For example, a π-shaped filter circuit composed of magnetic beads and capacitors, in addition, a 100Ω resistor can be used to replace magnetic beads when the conditions are not high.   (2) If the I/O port of the single-chip microcomputer is used to control the noise devices such as motors, the I/O port, and the noise source should be isolated.（ adding a π-shaped filter circuit）   (3) Pay attention to the crystal wiring. The crystal oscillator and single-chip microcomputer pin should as close as possible; the clock area should be isolated by grounding wire, crystal oscillator shell should be grounded and fixed. This measure can solve many difficult problems.   (4) Make reasonable partitions of the circuit board. Such as strong signal and weak signal, digital signal, and analog signal. Interference sources (such as motors and relays) and sensitive elements (such as microcontroller) should be isolated as far as possible.   (5) Separate the digital area from the analog area by landlines, and finally, connect to the power at one point. This principle is taken into account when the manufacturer makes the A/D and D/A chip pins arrangement.   (6) Single-chip microcomputer and large ground wire should be grounded separately to reduce mutual interference. High-power devices should be placed on the edge of the circuit board as far as possible.   (7) Use the anti-interference components such as magnetic beads, magnetic rings, power filters, and shielding covers in key places such as I / O portion, power lines, and circuit board connectors, which can significantly improve the anti-interference performance of the circuit.   2.3 Improve the Anti-interference Performance of Sensitive Devices To improve the anti-jamming performance of sensitive devices is to reduce the picking up of interference noise from the interference sources and to recover from abnormal state as soon as possible. The Usual Measures are as Follows: (1) Reduce the area of the loop in order to reduce the inductive noise.   (2) Power and ground wires should be as thick as possible, besides reducing the pressure drop, it is more important to reduce the coupling noise.   (3) The idle I / O port of SCM shouldn’t suspend, but connecting the ground or power supply. And the idle ends of other IC should be grounded or connected to power without changing the logic of the system.   (4) Using the power source monitoring and watchdog timer, such as IMP809, IMP706, IMP813, X25043, X25045, and so on, can greatly improve the anti-interference performance of the whole circuit.   (5) Under the condition that the speed can meet the requirement, the crystal oscillator of the single chip microcomputer is reduced and the low-speed digital circuit is chosen as far as possible.   (6) IC device is welded directly to the circuit board as far as possible.   III. Experience and Advice Software 1. Clearing the code space that is not commonly used, because this is equivalent to the NOP, can help programs recover when appearing program fleet.   2. Adding several NOP before the jump instruction, the same purpose as 1.   3. When there is no hardware WatchDog, an analog one can be used through software to monitor the operation of the program.   4. Dealing with the adjustment or setting of external device parameters, the parameters can be re-transmitted periodically in order to prevent the external device from making mistakes due to interference, so that the external device can be restored correctly as soon as possible.   5. Adding additive data to check anti-interference in Communication.   6. When there are communication lines, such as I2C or a three-wire system, it is found that the anti-interference effect of the Data line is better than that of the low one.   Hardware 1. The layout of grounding and power supply wires.   2. The decoupling of the circuit.   3. The separation of digital ground wire and analog ground wire.   4. Each digital element needs 104 capacitors between the grounding and the power supply.   5. In the applications with relays, especially in the case of high current, a 104 and diode can be combined between the relay coils to prevent the contact spark interference of the relay, and 472 capacitors installed at the contact point and the normal beginning.   6. To prevent the crosstalk of I / O port, the I / O port can be isolated by diode isolation, gate isolation, optocouple isolation, electromagnetic isolation, and so on.   7. Multi-layer board anti-jamming is certainly better than single-layer board, but its cost is several times higher.   8. Choosing an anti-jamming device is more effective than any other method.   FAQ   1. What is Circuit interference? Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.   2. What causes electrical interference? What Causes Interference? Interference occurs when undesired radio signals or electromagnetic "noise" sources are picked up by consumer electronics products -most often telephones, audio equipment, VCRs or TVs. It usually results in noise, unwanted voices or distorted TV pictures. In most cases, the source is nearby.   3. What is meant by circuit design? As circuit design is the process of working out the physical form that an electronic circuit will take, the result of the circuit design process is the instructions on how to construct the physical electronic circuit.   4. What is circuit design theory? In integrated circuit design automation, the term "circuit design" often refers to the step of the design cycle which outputs the schematics of the integrated circuit. Typically this is the step between logic design and physical design.   5. Which software is best for circuit design? a. Eagle b. Altium c. Proteus d. KiCad e. Cadence OrCAD PCB Designer f. DesignSpark g. Protel h. Cadstar i. Sprint-Layout j. PADS PCB   6. How does circuit design work? Digital electronic circuit design takes the electrical signals in the form of discrete values. The data are represented in the form of zeros and ones. Digital circuits extensively use transistors, interconnected to give create logic gates that provide the function of Boolean logic.   7. How long does it take to design a circuit? Programming the Micro-controller. Division of labor will make the work more efficient and specializations and expertise are more focused. Normally, it only takes hours to program the microcontroller of a simple circuit but complex circuit diagrams may take 2 to 3 days.   8. Is circuit design difficult? Designing a circuit is easy if you the basic working principle of each & every electronics components you're going to use. But making it efficient is a bit time-consuming. Once you know the rules, it's normally not too difficult. Of course, some circuits are more difficult than others.   9. What are the types of circuit? There are 5 Main Types of Electric Circuit – Close Circuit, Open Circuit, Short Circuit, Series Circuit and Parallel Circuit.   10. What is the process of a circuit? The process of circuit design can cover systems ranging from complex electronic systems all the way down to the individual transistors within an integrated circuit. ... Typically this is the step between logic design and physical design.   You May Also Like Can We Manage to Recycle PCB Boards for Avoiding Harming the Environment? 10 Things to Consider While choosing a PCB Prototype Service Some Guides for Beginners Before You Create A Printed Circuit Board(PCB) Industrial Chain and Development Trend of PCB in China

The insulated gate bipolar transistor (hereinafter referred to as IGBT) is a composite device of MOSFET and GTR. Thus it has the advantages of MOSFET and GTR, it is an ideal switch device to replace GTR, which is widely used at present with its ability to turn off, and it’s also widely used in all kinds of solid-state power supply.     Catalog   I. What is IGBT? II. The Driving Requirement of IGBT III. The Overcurrent Protection Analysis of IGBT IV. Simulation and Experiment FAQ   I. What is IGBT?   The insulated gate bipolar transistor (hereinafter referred to as IGBT) is a composite device of MOSFET and GTR. Thus it has the advantages of MOSFET, including fast operation speed, high switching frequency, high input impedance, simple drive circuit, and good thermal temperature; it also contains the advantages of GTR, like large current-carrying capacity and high blocking voltage. It is an ideal switch device to replace GTR, which is widely used at present with its ability to turn off and is also widely used in all kinds of solid-state power supply.   And it requires a reasonable drive circuit, but its improper control may cause damage, such as IGBT damage due to overcurrent, and affects the performance of the whole machine. In a word, the drive circuit is very important to IGBT. So this paper mainly discusses the driving and short-circuit protection of IGBT, based on the analysis of its working principle, then designs and simulates the overcurrent protection of the drive circuit.     Electronic Basics #28: IGBT and when to use them     II. The Driving Requirement of IGBT   Driving Requirement IGBT is a voltage-type control device. To make IGBT turn on and off safely and reliably, the driving circuit must meet the following conditions.  And the gate capacitance of IGBT is much larger than that of MOSFET. To increase the switching speed, it is necessary to have a suitable gate bias voltage and gate series resistance.   Gate Voltage In any case, the gate drive voltage in the open state can not exceed the limited value (generally 20V) given by the parameter table, and the optimal gate forward-bias voltage is 15 V ±1.5V. This value is sufficient to allow IGBT to reach saturation and then getting conduction, which can minimize the conduction loss. In the case of gate voltage is cutting off with the value of zero, to reduce the turn-off time and improve the withstand voltage and anti-interference ability of IGBT, a reverse voltage of -5 ~ -15 V can be added between the gate and the source electrode when the IGBT is in a blocking state.   Gate Series Resistance Core The selection of appropriate gate series resistance (RG) is very important for the drive of IGBT. The effect of RG on switching loss is shown in Fig.1. Fig. 1 The Effect of RG on Switching Loss It is the dynamic current of charging and discharging the input capacitance rather than the DC current that is required in a static state, and the input impedance of IGBT is up to 109 ~ 1011. In this case, the DC gain can reach 108 ~ 109, almost without any power consumption.   To decrease the steepness of the front and rear edges of the control pulse, prevent oscillation and reduce the voltage tip pulse with a large IGBT collector, it is necessary to add a gate series resistor RG. When the RG increases, the on-off time will prolong and the energy consumption of the IGBT will increase; in turn, the RG reduces, the di/dt will increase and may damage IGBT.   Thus, according to the current capacity and voltage rating, and switching frequency of IGBT, it is necessary to select a suitable RG, usually from dozens of ohms to hundreds of ohms. To get a more specific value of RG, it is suggested to refer to the device manual. Fig.2 Main Circuit of Inverter Power Supply   Requirements for Driving Power The switching process of IGBT consumes a certain amount of power from the driving power supply. The difference between the gate forward bias voltage and the reverse bias voltage is the △VGE; working frequency is f, the gate capacitance is CGE; and the minimum peak current of the power supply is:     Overcurrent Protection for IGBT The overcurrent protection of IGBT is limiting the short-circuit current and its I-V track to the short circuit safe working area when the device overflows, and the IGBT is turned off before the device is damaged to avoid the damage of the switch tube. When the upper and lower arms conducting, the power supply voltage is almost all added to the two ends of the switch, at this time, the larger the short circuit current is, the smaller the saturation voltage drop will be, during this time, the device would be damaged due to the large current.     III. The Overcurrent Protection Analysis of IGBT   Based on the above analysis, an IGBT drive circuit which contains isolated optocoupler and over-current protection has been put forward in this article, as shown in Fig.3. Fig.3 The Drive and Overcurrent Protection Circuit of IGBT  In Fig.3, the high-speed optocoupler 6N137 realizes the electrical isolation of the input and output signals, which is suitable for high-frequency applications. The main drive circuit adopts push-pull output mode, which effectively reduces the output impedance of the drive circuit, improves the driving ability, and makes it suitable for the drive of high power IGBT.   The over-current protection circuit uses the principle of desaturation of the collector. When an over-current occurs, the IGBT will be turn off. The V1, V3and V4 constitute the driving pulse amplifier circuit; V1 and R5 constitute an emitter follower. The emitter follower provides a fast current source, which reduces the turn-off time. Using the collector desaturation principle, D1, R6, R7, and V2 form a short-circuit signal detection circuit. D1 is a fast recovery diode, to prevent the high voltage on the collector from running into the driving circuit when IGBT is turned off.   In order to prevent the power device from being misled by static electricity, bidirectional voltage regulators D3 and D4 are connected in parallel between the gate sources.   Normal When the control circuit sends a high-level signal, the optocoupler 6N137 turns on, V1, V2 turns off, V3 turns on and V4 turns off. And the drive circuit provides IGBT a driving voltage of +15V to turn it on. When the control circuit sends a low level signal, the optocoupler 6N137 turns off, V2 and V3 conduct, and the drive circuit provides a voltage of -5v to IBGT, making IGBT shut down.   Overcurrent When a short-circuit fault exists, the voltage of 15V is almost all added to the IGBT. At this time, the voltage of V2 cuts off in the short circuit detection circuit, and the electric potential of point A depends on the partial voltage of D1, R6, R7, and VCES.  When the main circuit works normally and the IGBT is on, the A point is kept low, which is lower than the B point potential. All A1 output low level, this time V5 cuts off, and the C point is high level.   So when operating normally, the input to the optocoupler 6N137 is always consistent with the output. When overcurrent occurs, the IGBT collector is desaturated, A point potential rises, when it is higher than B potential ( the setting potential), that is, when the current exceeds the designed fixed value, the A1 overturns and outputs a high level, meanwhile, V5 is switched on, thereby making C in a low potential state. The input signal to the optocoupler 6N137 is always low level regardless of whether the control circuit is sent to a high level or a low level to turn off the power tube. Thus, over-current protection is achieved until the circuit is troubleshot and then restarted.   Fig. 4 Strong Driving Circuit of IGBT with Short-Circuit Protection   IV. Simulation and Experiment   Input to the drive circuit with a high level of 15V and a low level of -5V square wave signal. The output waveform of IGBT is shown in Fig.5  Fig.5 IGBT Output Signal According to the above principle and analysis, the actual output waveform of the circuit is shown in Fig.6  Fig.6 Actual Circuit Output Waveform Conclusion (1) Providing -5V and +15V driving voltage for IGBT to ensure IGBT's turn on and off. (2) Having over-current protection to prevent the IGBT from being damaged when the current is overcurrent. (3) Using in a wide range because the circuit can dynamically adjust the maximum current according to the load. (4) Adopting discrete components as the driving circuits to reduce the cost of the whole system.     FAQ   1. How does an insulated gate bipolar transistor work? The IGBT combines the simple gate-drive characteristics of power MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors. The IGBT combines an isolated-gate FET for the control input and a bipolar power transistor as a switch in a single device.   2. Which insulated gate bipolar transistor? IGBTs are widely used as switching devices in the inverter circuit (for DC-to-AC conversion) for driving small to large motors. IGBTs for inverter applications are used in home appliances such as air conditioners and refrigerators, industrial motors, and automotive main motor controllers to improve their efficiency.   3. How do I trigger IGBT?   An IGBT is simply switched “ON” and “OFF” by triggering and disabling its Gate terminal. A constant +Ve voltage i/p signal across the 'G' and the 'E' will retain the device in its “ON” state, while deduction of the i/p signal will cause it to turn “OFF” like BJT or MOSFET.   4. Why use an IGBT instead of a Mosfet? The main advantages of IGBT over a Power MOSFET and a BJT are: 1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.   5. Why IGBT is used an inverter? The Insulated Gate Bipolar Transistor (IGBT) is used in VFD inverter modules as the preferred electronic power switch for the following reasons. ... The IGBT has a fast switching speed. This minimises switching losses and allows for high switching frequencies which is good for motor harmonic and noise reduction.   6. What is difference between IGBT and SCR? SCR is a silicon control rectifier and igbt is a insulated gate bipolar transistor. ... scr has anode ,cathode and gate and igbt has base ,emitter, gate ,and collector. In the both devices gate terminal is used for triggering. Scr has only one insultive layer but igbt has 2 insulated silicon layers.   7. What is IGBT principle? IGBT Principle of Operation：IGBT requires only a small voltage to maintain conduction in the device unlike in BJT. The IGBT is a unidirectional device, that is, it can only switch ON in the forward direction. This means current flows from the collector to the emitter unlike in MOSFETs, which are bi-directional.   8. What causes IGBT failure? The failure modes for the IGBT are in the form of degradation of certain key electrical parameters (e.g., leakage current, threshold voltage) or the loss of functionality (inability to turn-off). The failure causes can be due to environmental conditions or operating conditions.   9. Is IGBT unipolar or bipolar? The IGBT cannot conduct current in the reverse direction (from emitter to collector) even with a positive Vge applied to it, because it has a bipolar-type structure.   10. Which IGBT used in VFD? IGBT (insulated gate bipolar transistor) provides a high switching speed necessary for PWM VFD operation. IGBTs are capable of switching on and off several thousand times a second. A VFD IGBT can turn on in less than 400 nanoseconds and off in approximately 500 nanoseconds.   11. Can we use IGBT instead of Mosfet? Due to the higher usable current density of IGBTs, it can usually handle two to three times more current than a typical MOSFET it replaces. This means that a single IGBT device can replace multiple MOSFETs in parallel operation or any of the super-large single power MOSFETs that are available today.   12. How fast can an IGBT switch? The typical switching time of IGBT is about hundreds of nanoseconds and the value varies with load current, junction temperature, and other factors [17–20]. However, the change of IGBT switching time is very small [4,5] (range from several to tens of nanoseconds) when the health status of the IGBT module changes.   13. Is IGBT faster than Mosfet? When compared to the IGBT, a power MOSFET has the advantages of higher commutation speed and greater efficiency during operation at low voltages. ... The IGBT combines the simple gate-drive characteristics found in the MOSFET with the high-current and low-saturation-voltage capability of a bipolar transistor.   14. How many IGBT are in a VFD? Six IGBTs. In a typical six pulse drive there are six IGBTs pulsing voltage up to 15,000 times per second. Since their introduction in the 1980's, IGBTs have literally switched up the market and now play a large role in many modern day power electronics applications where speed and process control are needed.   15. What is the function of IGBT? The IGBT combines, in a single device, a control input with a MOS structure and a bipolar power transistor that acts as an output switch. IGBTs are suitable for high-voltage, high-current applications. They are designed to drive high-power applications with a low-power input.   16. Is IGBT a rectifier? IGBTs have a pretty good current handling capacity when compared to standard BJTs (Bipolar junction transistor) and MOSFETs (metal–oxide–silicon transistor). IGBTs are devices whose switching is fully controlled electronically. Most standard rectifiers in the market are typically 6-pulse rectifiers.   17. How many types of IGBT are there? two types. The IGBT is classified as two types based on the n+ buffer layer, the IGBTs that are having the n+ buffer layer is called the Punch through IGBT (PT-IGBT), the IGBTs that does not have an n+ buffer layer are called the Non-Punch Through- IGBT (NPT- IGBT).   18. How do you prevent IGBT failure? IGBT turn-off requires that the IGBT be driven to the cutoff region of operation so that it can successfully block the reverse high voltage across it once the high-side IGBT has turned on. In principle this can be achieved by reducing the IGBT gate-emitter voltage to 0 V.   19. What is the difference between unipolar and bipolar devices? As their name implies, Bipolar Transistors are “Bipolar” devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a “Unipolar” device that depends only on the conduction of electrons (N-channel) or holes (P-channel).   20. What is IGBT and Igct? GTO stands for Gate Turn-Off Thyristor, IGCT stands for Insulated Gate Commutated Thyristor and IGBT stands for Insulated Gate Bipolar Transistor. The comparison between the three devices are derived with respect to symbol, characteristic, advantages, disadvantages and applications.   You May Also Like The First Fully 2D FETs Lead A Faster Electronic Future The First Printed 2D Transistor Is Discovered by Researchers The First Chemical Circuit Developed Smarter transistors could be three times more efficient

Warm hints: The word in this article is about 3000 words and reading time is about 12 minutes.     This article would introduce you different kinds of power supply circuits.   Catalog   I. Circuit Arrangement of Switching Power Supply II. The Principle of the Input Circuit and the Common Circuits 2.1 Principle of AC Input Rectifier Filter Circuit 2.1.1 Lightning Protection Circuit 2.1.2 Input Filter Circuit 2.1.3 Rectifier Filter Circuit 2.2 Principle of DC Input Filter Circuit 2.2.1 Input Filter Circuit 2.2.2 The Anti-surge Circuit III. Power Conversion Circuits 3.1 The Working Principle of MOS Tube 3.2  Common Schematic Diagram 3.3 Working Principle 3.4 Push-pull Power Conversion Circuit 3.5 Power Conversion Circuit with Transformer Driver IV. Output Rectifier Filter Circuit 4.1 Forward Rectifier Circuit 4.2 Flyback Fectifier Circuit 4.3 Synchronous Rectifier Circuit V. Principles of Steady-voltage Loop 5.1 Schematic Diagram of Feedback Circuit 5.2 Working Principles VI. Short Circuit Protection Circuits 6.1 Current-limiting Circuit 6.2 Short Circuit Protection for Low-power Circuit 6.3 Short Circuit Protection for Medium-power Circuit 6.4  Common Current-limiting, Short-circuit Protection Circuit 6.5 Current Transformer Sampling Current Protection Circuit VII. Output Current Limiting Protection VIII. Output Overvoltage Protection Circuits 8.1 SCR Trigger Protection Circuit 8.2 Optocoupler Protection Circuit 8.3 Output Voltage Limiting Protection Circuit 8.4 Output Overvoltage Lockout Circuit IX. Power Factor Correction Circuit (PFC) 9.1 Schematic Diagram of PFC Circuit 9.2 The Working Principles X. Input Under-voltage and Overvoltage Protection 10.1 Schematic Diagram 10.2 The Working Principles FAQ       I. Circuit Arrangement of Switching Power Supply   The main circuit of the switch-mode power supply is composed of an input EMI filter, rectifier filter circuit, power conversion circuit, and PWM controller circuit, output rectifier filter circuit. The auxiliary circuits include the input & output Undervoltage protection circuit, the output overcurrent protection circuit, the output short circuit protection circuit, and so on.   The block diagram of switching power supply circuit arrangement is as follows:   FIG.1 Block diagram of switching power supply circuit arrangement   II. The Principle of the Input Circuit and the Common Circuits   2.1 Principle of AC Input Rectifier Filter Circuit 2.1.1    Lightning Protection Circuit When there is a lightning strike, the circuit composed of MOV1, MOV2, MOV3, F1, F2, F3, and FDG1 is used to provide protection against the resulting high voltage introduced into the power supply through the electrical grid.   When the voltage applied to the two ends of the piezoresistor exceeds its operating voltage, the resistance value will decrease, making the high voltage energy be consumed on the piezoresistor; if the current is too large, the F1, F2, and F3 will burn out to protect the following circuits. 2.1.2     Input Filter Circuit The double Pi filter network composed of C1, L1, C2 and C3 is mainly used to suppress the electromagnetic noise and clutter signal of the input power supply to prevent its interference to the power supply, and also to prevent the interference of the high-frequency clutters generated by the power supply itself to the electrical grid. The C5 will start to be charged when the power is turned on, producing a large instantaneous current, which is called surge current, but with an RT1 (thermistor) it can be effectively prevented. Because the instantaneous energy is all consumed on the RT1, after a certain time the resistance of RT1 will decrease as the temperature rises (RT1 is a negative temperature coefficient device) and the energy consumed by RT1 will be very small at this time, to make sure the following circuits work normally.     2.1.3   Rectifier Filter Circuit After the AC voltage is rectified by BRG1 and filtered by C5, a purer DC voltage can be obtained. If the C5 capacity becomes smaller, the output AC ripples increase with it.     2.2 Principle of DC Input Filter Circuit FIG.3 The schematic of rectifier circuit   2.2.1   Input Filter Circuit The double Pi filter network composed of C1, L1and C2 is mainly used to suppress the electromagnetic noise and clutter signal of the input power supply to prevent its interference to the power supply, and also to prevent the interference of the high-frequency clutters generated by the power supply itself to the electrical grid. C3 and C4 are Safety Capacitors and the L2, L3 are Differential Mode Inductors.   2.2.2   The Anti-surge Circuit This anti-surge circuit is composed of R1, R2, R3, Z1, C6, Q1, Z2,  R4, R5, Q2, RT1 and C7. At the instant of switch-on, Q2 does not conduct due to the presence of C6, and the current forms a loop through the RT1. Q2 turns on when the voltage on C6 is charged to Z1's steady voltage value. If C8 leaks or the following circuits are short-circuited, the voltage drop generated by the instantaneous current at the instant of switch-on on RT1 causes the Q1 conducted, so that Q2 does not have a gate voltage and does not conduct, making the RT1 burnt out in a very short time to protect the following circuits.   III. Power Conversion Circuits   3.1   The Working Principle of MOS Tube At present, the most widely used insulated gate FET is MOSFET, which uses the electroacoustic effect that occurs on the semiconductor surface to work, making it also known as surface field effect transistor. Because its gate is in a nonconducting state, the input resistance can be greatly increased up to 105 ohms. The MOSFET uses the gate-source voltage to change the amount of charge induced on the semiconductor surface to control the drain current.   3.2   Common Schematic Diagram FIG.4 Schematic of power conversion circuit    3.3  Working Principle The buffer composed of R4, C3, R5, R6, C4, D1, and D2 are connected in parallel with the MOS transistor switches, so that the voltage stress of the switch transistor and EMI are reduced, without secondary breakdown occurring. When the switch Q1 is turned off, the primary coil of the transformer is prone to generate peak voltages and spike currents. These components are combined to absorb the peak voltage and current well. The peak current signal measured from R3 participates in the duty cycle control of the current operating cycle and is therefore the current limit of the current operating cycle. When the voltage on R5 reaches 1V, the UC3842 stops working and switch Q1 turns off immediately.   The junction capacitances CGS and CGD in R1 and Q1 together form an RC network. The charge and discharge of the capacitor directly affects the switching speed of the switch. If R1 is too small, it will cause oscillation and electromagnetic interference will be great. If R1 is too large, the switching speed of the switching tube will be reduced. Z1 usually limits the GS voltage of the MOS transistor to less than 18V, thus protecting the MOS transistor.   The gate-controlled voltage of Q1 is a saw wave. The larger the duty cycle is, the longer the Q1 conduction time is, the more energy the transformer stores. When Q1 is turned off, the transformer releases energy through D1, D2, R5, R4, and C3 and at the same time, it also achieves the goal of resetting the magnetic field, which prepares the transformer for the next storage and transfer of energy. According to the output voltage and current, the IC adjusts the duty cycle of 6-pin sawtooth wave, thus stabilizing the output current and voltage of the complete machine.   C4 and R6 are voltage surge absorption loops.   3.4  Push-pull Power Conversion Circuit Fig.5 Schematic diagram of push-pull power conversion circuit Q1 and Q2 will be turned on in turn.   3.5  Power Conversion Circuit with Transformer Driver FIG.6 Schematic diagram of power conversion circuit with transformer driver T2 is the transformer driver, T1 is the switch-mode transformer, TR1 is the current loop .   IV. Output Rectifier Filter Circuit   4.1   Forward Rectifier Circuit FIG.7 Schematic diagram of forward rectifier circuit T1 is a switch-mode transformer, its primary and secondary sides are in a same phase. D1 is a rectifier diode, D2 is a flyback diode and R1, C1, R2 and C2 form a despiker circuit. L1 is a freewheeling inductor and C4, L2, and C5 form a π filter.   4.2  Flyback Fectifier Circuit FIG.8 Schematic diagram of flyback fectifier circuit T1 is a switch-mode transformer, and the primary and secondary sides are opposite. D1 is a rectifier diode, and R1 and C1 form a despiker circuit. L1 is a a freewheeling inductor, R2 is adummy load and C4, L2 and C5 form a π type filter.   4.3   Synchronous Rectifier Circuit FIG.9 Schematic diagram of synchronous rectifier circuit Working principle: When the upper end of the secondary winding of transformer is positive, the current through C2, R5, R6 and R7 makes Q2 turned on and form a loop. Q2 is the rectifier and the Q1 gate is turned off due tothe reverse bias. When the lower end of second wingding is positive, the current through C3, N4 and R2 makes Q1 conducted as a freewheeling diode. The Q2 gate is turned off due to the reverse bias. L2 is a freewheeling inductor, C6, L1 and C7 form a π filter and R1, C1, R9 and C4 form a despiker circuit.   V.  Principles of Steady-voltage Loop   5.1  Schematic Diagram of Feedback Circuit FIG.10 Schematic diagram of feedback circuit 5.2  Working Principles When the output U0 is increased, the voltage of pin 3 of U1 chip is increased either after dividing voltage with these sampling resistors R7, R8, R10 and VR1, until exceeding the reference voltage of pin 2 of U1 chip, it begins to output a high level, turning the Q1 and photoelectric triode on, and lighting the optocoupler OT1 and LED. Accordingly, the potential of pin 1 of UC3842 becomes lower and therefore decreases the duty cycle of pin 6 of U1 chip and U0.    On the contrary, when the output U0 is decreased, the voltage of pin 3 of U1 chip is decreased either until it exceeds the reference voltage of pin 2 of U1 chip, it begins to output a low level, Q1 and photoelectric triode are not conducting, and optocoupler OT1 and LED do not shine. Accordingly, the potential of pin 1 of UC3842 becomes higher and therefore increases the duty cycle of pin 6 of U1 chip and U0. Repeatedly, so that the output voltage remains stable. Regulating VR1 can change the output voltage.   Feedback loop is an important circuit that affects the stability of switching power supply. If the feedback resistors and capacitors are wrong, missed or false soldered, self-excited oscillations will occur, resulting in fault phenomena, such as abnormal waveforms, oscillations within empty or full load condition and unstable output voltage.   VI. Short Circuit Protection Circuits   6.1  Current-limiting Circuit In the case of short circuit at the output end, PWM control circuit can limit the output current within a safe range. There are many ways to  realize the current limiting. When the current limiting circuit does not work in short circuit, all we can do is to add additional circuits.   6.2  Short Circuit Protection for Low-power Circuit FIG.11 Schematic diagram of low-power short-circuit protection circuit When the output circuit is shorted, the output voltage disappears, the optocoupler OT1 does not turn on, the voltage of pin 1 of UC3842 rises to about 5V, and the partial voltages of R1 and R2 exceed the TL431 reference, making it conductive, the VCC potential of pin 7 of UC3842 is pulled down, and the IC stops operating. After UC3842 stopped working, the potential of pin 1 disappeared, TL431 did not conduct, and the potential of UC38427 increased, making UC3842 restart, and go round and begin again, until the short-circuit phenomenon disappears, then the circuit automatically returns to normal operation.   6.3  Short Circuit Protection for Medium-power Circuit FIG.12 Schematic diagram of medium-power short-circuit protection circuit When the output is short-circuited, the voltage of pin of UC3842 rises. When the potential of pin 3 of U1 chip is higher than that of pin 2, the comparator inverts the output high level of pin 1 to charge C1. When the voltage across C1 exceeds the pin 5 reference voltage, the pin 7 of U1 chip outputs low level. The voltage of pin 1 of UC3842 begins to be lower than 1V and UC3842 stops working, making the output voltage be zero, and go round and begin again, until the short-circuit phenomenon disappears, and the circuit begins to work normally. R2 and C1 are charge and discharge time constants respectively, and the short circuit protection will not work if the resistance is not correct.   6.4  Common Current-limiting, Short-circuit Protection Circuit FIG.13 Schematic diagram of protection circuit 1 When the output circuit is short-circuited or overcurrent, the primary current of the transformer increases, the voltage drop across R3 increases, the voltage at pin 3 increases, and the duty cycle of pin 6 of UC3842 increases. When the voltage at pin 3 exceeds 1V, the UC3842 turns off and without output.   6.5  Current Transformer Sampling Current Protection Circuit The current transformer sampling current protection circuit which has low power consumption but high cost, and the circuit is often complicated. FIG.14 Schematic diagram of protection circuit 2 The larger the output current is (the extreme case refers to short circuit), the higher the voltage sensed by the TR1 secondary coil. When the voltage of pin 3 of UC3842 exceeds 1 volt, the UC3842 stops working. Go round and begin again, until the short-circuit or overload disappears, the circuit recovers itself.   VII. Output Current Limiting Protection FIG.15 Schematic diagram of protection circuit 3 The above is a common output current limiting protection circuit, and its working principle is as follows:   When the output current is too high, the voltage across the RS (manganese copper wire) rises, the voltage of pin 3 of the U1 chip is higher than the reference voltage of pin 2. Pin 1 of the U1 chip outputs a high voltage, which makes Q1 turned on, and the optoelectronic effect occurs on the optocoupler, the voltage of pin 1 of UC3842 is reduced, together with the output voltage, to achieve the goal of overload protection or current limiting.     VIII. Output Overvoltage Protection Circuits   The role of the output overvoltage protection circuit is to limit the output voltage to a safe value when the output voltage exceeds the design value.    When an internal voltage regulator loop of a switching power supply fails or an overvoltage occurs due to a user's improper operation, an overvoltage protection circuit is used to protect against damage to downstream electrical equipment.   The most commonly used overvoltage protection circuits are as follows:   8.1  SCR Trigger Protection Circuit FIG.16 Schematic diagram of protection circuit 4 As shown above, when the output of Uo1 rises, the Zener diode (Z3) breaks down and it is pulled into conduction, letting the control terminal of the Silicon Controlled Rectifier reach the trigger voltage, so the SCR turns on and the Uo2 is shorted to ground. Then the overcurrent or short circuit protection circuit will work and stop the operation of the entire power supply circuit. When the overvoltage condition on the output terminals is eliminated, the trigger voltage of the control terminal of the thyristor is discharged to the ground through R, and the thyristor returns to the off state.   8.2  Optocoupler Protection Circuit FIG.17 Schematic diagram of protection circuit 5A FIG.18 Schematic diagram of protection circuit 5B As shown in the above figure, when an phenomenon of overvoltage occurs in the Uo, the Zener breaks down and conducts current through the optocoupler (OT2) and R6 to the ground, lightening the light-emitting diode of the photocoupler, which causes the phototransistor of the photocoupler to conduct. The base of Q1 is turned on and the voltage of pin 3 of UC3842 is reduced, turning off the IC and the entire power supply while Uo is zero, and go round and begin again.   8.3  Output Voltage Limiting Protection Circuit FIG.19 Schematic diagram of protection circuit 6 The output voltage limiting protection circuit is shown in the diagram. When the output voltage rises, zener and optocoupler are on, and the base of Q1 turns on either due to a driving voltage according. The voltage of pin 3 of UC3842 rises and the output drops. When the zener is not conducting, the voltage of pin 3 of UC3842 drops and the output voltage rises. As time goes by, the output voltage will be stable within a range (depending on the zener's value).   8.4  Output Overvoltage Lockout Circuit FIG.20 Output overvoltage lockout circuit A FIG.21 Output overvoltage lockout circuit B The working principle is shown in Figure A is that when the output voltage Uo rises, the Zener and optocoupler turn on, and then go with the base of Q2, because of which the base of Q1 is on due to the drop of voltage.   Q2 is on all the time after the voltage of Vcc is through R1, Q1, and R2, making the pin 3 of UC3842 always be conducted with high level and therefore stop working.   In Figure B, the voltage of pin 3 of the U1 chip raises due to big rises of Uo, and pin 1 outputs a high level. Because of the presences of D1 and R1, the pin 1 of U1 chip is always on and outputs a high level, so it is always low and then it stops working. Is it positive feedback?     IX. Power Factor Correction Circuit (PFC)   9.1 Schematic Diagram of PFC Circuit FIG.22 Schematic diagram of PFC circuit 9.2  The Working Principles The input voltage is rectified by an EMI filter composed of L1, L2, L3, and so on and a BRG1, one part of which is then fed into the PFC inductor and another part of which is fed into the PFC controller as the sampling of the input voltage to adjust the duty cycle of the control signal before divided by R1 and R2, that is to change them on and off time of Q1 and to stabilize the output voltage of PFC.   L4 is a PFC inductor that stores energy when Q1 is on and releases energy when Q1 is switched off. D1 is the start diode. D2 is the PFC rectifier diode, and C6, C7 are filtered. One part of the PFC voltage is sent to the downstream circuit, and another part of it is fed into the PFC controller as the sampling of the output voltage before divided by R3 and R4, to adjust the duty cycle of the control signal and to stabilize the output voltage of PFC.     X. Input Under-voltage and Overvoltage Protection   10.1  Schematic Diagram FIG.23 Schematic diagram of input undervoltage and overvoltage protection circuit   10.2  The Working Principles The input under-voltage and overvoltage protection principles of the switching power supply of AC input and DC input are almost the same. The sampling voltages of the protection circuits all come from the same input filtered voltage.   The sampling voltage is divided into two ways, one way is fed into pin 3 of the comparator after divided by R1, R2, R3, and R4. If the sampling voltage is higher than the reference voltage of pin 2, then pin 1 of the comparator will output a high level to control the main controller and make the main controller turned off, so there is no power output. The other way is fed into pin 6 of the comparator before it is divided by R7, R8, R9, and R10.   If the sampling voltage is lower than the reference voltage of pin 5, then pin 7 of the comparator will output a high level to control the main controller and make it turned off, so there is no power output.   How To Make a Switching Power Supply     FAQ   1. What are the 3 types of power supply? There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.   2. What is meant by switch mode power supply? A switch mode power supply is a power converter that utilises switching devices such as MOSFETs that continuously turn on and off at high frequency; and energy storage devices such as the capacitors and inductors to supply power during the non-conduction state of the switching device.   3.What are the advantages and disadvantages of switch mode power supply? Advantages & disadvantages of switch mode power supply (SMPS) a. The switch mode power supply has a smaller in size. b. The SMPS has light weight. c. It has a better power efficiency typically 60 to 70 percent. d. It has a strong anti interference. e. SMPS has wide output range. f. Low heat generation in SMPS.   4. What is a DC switching power supply? A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor.   5. What is the difference between a switching power supply and a linear power supply? Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges.   6. Do I need a switching power supply? The switching power supply implies higher efficiency due to the high switching frequency, enabling it to use a smaller, less-costly high-frequency transformer as well as lighter, less-costly filter components. Switching power supplies contain more overall components, therefore are usually more expensive.   7. Is a switching power supply regulated? A switch mode power supply regulates an output voltage with pulse width modulation (PWM). This process creates high-frequency noise but it provides a high-efficiency rating in a small form factor. ... The low DC voltage is finally converted into a steady DC output with another set of diodes, capacitors, and inductors.   8. How do I know if my power supply is regulated? You can generally stick one probe into the middle of the connector, and hold the other against the outside. With a few exceptions, the middle is positive, so use the red lead there, and use the black lead on the outside shell. Regulated supplies, without any load, should measure very close to the target voltage of 12v.   9. Can I use a switching power supply to drive a DC motor?   A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC.   10. Are switch mode power supplies any good? Switch mode power supplies, SMPS provide improved efficiency & space saving over traditional linear supplies, but care has to be taken to ensure noise on the output is low. Switch mode power supplies are widely used because of the advantages they offer in terms of size, weight, cost, efficiency and overall performance.   You May Also Like: Transformers Basics: Construction, Types, Materials and Design Modeling and Control of Full Bridge Push-Pull Bi-Directional DC/DC Converter Review and Application of Electronic skin How to Drive Thermostat by Using Solid State Relay