? Internal structure of switching power supply
The main introduction here is only DC switching power supply, whose function is to convert the original power supply with poor quality of electricity (coarse power), such as utility power supply or battery power supply, into DC voltage of higher quality (fine power) to meet the requirements of the equipment. The core of a DC switching power supply is the DC/DC converter. Therefore, the classification of DC switching power supply is dependent on the classification of DC/DC converter. In other words, the classification of DC switching power supply and DC/DC converter are basically the same, and the classification of DC/DC converter is basically the classification of DC switching power supply. DC DC/DC converter according to the input and output of the electrical isolation between whether or not can be divided into two categories: a class of isolation known as isolated DC/DC converter; the other is not isolated known as non-isolated DC/DC converter. Isolated DC/DC converter can also be categorized by the number of active power devices. Single-tube DC/DC converter forward (Forward) and flyback (Flyback) two kinds. Double tube DC/DC converter has a double tube forward (DoubleTransistor Forward Converter), double tube flyback (Double Transistr Flyback Converter), push-pull (Push-Pull Converter) and half-bridge (Half-Bridge) four. Converter) four kinds. Four-pipe DC/DC converter is a full-bridge DC/DC converter (Full-Bridge Converter). Non-isolated DC/DC converter, according to the number of active power devices, can be divided into single-tube, dual-tube and four-tube three categories.? Switching Power Supply Internal Structure Diagram
There are six types of single-tube DC/DC converters***, namely, Step-Down (Buck) DC/DC converter , Boost (Boost) DC/DC converter, Boost-Buck (Buck Boost) DC/DC converter, Cuk DC/DC converter, Zeta DC/DC converter and SEPIC DC/DC converters. Among these six types of single-tube DC/DC converters, Buck and Boost type DC/DC converters are the basic ones from which Buck-Boost, Cuk, Zeta, and SEPIC type DC/DC converters are derived. Two-tube DC/DC converters have two-tube series connected boost (Buck-Boost) DC/DC converters. Four-tube DC/DC converter commonly used full-bridge DC/DC converter (Full-Bridge Converter). Isolated DC / DC converter in the realization of the output and input electrical isolation, usually using a transformer to achieve, due to the transformer has the function of voltage, so it is conducive to expanding the converter's output range of applications, but also to facilitate the realization of the different voltages of the multiple outputs, or the same voltage of a variety of outputs. In the power switching tube voltage and current quota is the same, the output power of the converter is usually proportional to the number of switching tubes used. So the more the number of switching tubes, the greater the output power of the DC/DC converter, four-tube type than two-tube output power is twice as large as a single-tube type output power is only four-tube type of 1/4. non-isolated converter and the combination of isolated converters, you can get a number of characteristics of a single converter does not have. According to the transmission of energy, DC/DC converter has a unidirectional transmission and bi-directional transmission of two kinds. DC/DC converters with bi-directional transmission can transmit power from the power supply side to the load side, as well as from the load side to the power supply side. DC/DC converters can also be categorized into self-excited and other-controlled types. With the help of the converter itself positive feedback signal to realize the switching tube self-sustained periodic switching converter, called self-excited converter, such as Royer (Royer) converter is a typical push-pull self-excited converter. He controlled DC / DC converter in the switching device control signal, is generated by the external specialized control circuit. According to the switching conditions of the switching tube, DC/DC converter can be divided into hard switching (Hard Switching)? Switching Power Supply
and Soft Switching (Soft Switching). Hard switching DC/DC converter switching device is under voltage or current flow, turn on or off the circuit, so in the process of turning on or off will produce a large overlap loss, the so-called switching loss (Switching loss). When the operating state of the converter is certain, the switching loss is also certain, and the higher the switching frequency, the greater the switching loss, and at the same time in the switching process will also provoke the circuit distribution of inductance and parasitic capacitance oscillations, bringing additional losses, therefore, the switching frequency of the hard-switching DC/DC converter can not be too high. Soft-switching DC/DC converter switching tube, in the turn-on or turn-off process, either the voltage added to it is zero, i.e., zero-voltage switching (ZVS), or the current through the switching tube is zero, i.e., zero-current-switching (ZCS). This soft-switching method can significantly reduce the switching losses, as well as the oscillations provoked during the switching process, so that the switching frequency can be significantly increased, creating the conditions for the miniaturization and modularization of the converter. The power field effect tube (MOSFET) is a more widely used switching device, it has a high switching speed, but also has a large parasitic capacitance. It is off, the role of the external voltage, its parasitic capacitance is full of electricity, if it is not before the opening of this part of the charge will be discharged, it will be consumed in the internal device, which is the capacitive turn-on loss. In order to minimize or eliminate this loss, it is advisable to use the zero-voltage turn-on method (ZVS) for power field-effect transistors. Insu1ated Gate Bipo1ar tansistor (IGBT) is a composite switching device, the current trailing at shutdown will lead to large shutdown loss, if the current flowing through it is reduced to zero before shutdown, the switching loss can be significantly reduced, so it is appropriate to use zero-current (ZCS) shutdown mode for the IGBT. IGBT shutdown at zero voltage can also reduce the shutdown loss, but MOSFET turn-on at zero current can not reduce the capacitive turn-on loss. ResonantConverter (RC), Quasi-Resonant Converter (QRC), Multi-Resonant Converter (MRC), Zero Voltage Switching PWM Converter (ZVS PWM Converter), Zero Current Switching PWM Converter (ZCSC), and Zero Voltage Switching PWM Converter (ZVS PWM Converter). Current-Switching PWM Converter (ZCS PWM Converter), Zero-Voltage-Transition (ZVT) PWM Converter, and Zero-Voltage-Transition (ZVT) PWM Converter are soft-switching DC converters. The development of power electronic switching devices and zero-switching converter technology has led to the development of high-frequency switching power supplies.4 Basic CompositionEditSwitching power supplies are roughly composed of the main circuit,? Switching power supply
control circuit, detection circuit, auxiliary power supply four major components.1, the main circuit inrush current limiting: limit the power supply on the instantaneous input side of the inrush current. Input Filter: Its function is to filter the stray waves existing in the power grid and hinder the stray waves generated by the machine to be fed back to the power grid. Rectification and Filtering: Directly rectify the AC power from the grid to a smoother DC power. Inverter: The rectified DC power is changed into high frequency AC power, which is the core part of high frequency switching power supply. Output rectification and filtering: according to the needs of the load, to provide a stable and reliable DC power supply. 2, on the one hand, the control circuit from the output side of the sampling, and the set value for comparison, and then go to control the inverter, change its pulse width or pulse frequency, so that the output is stable, on the other hand, according to the test circuit to provide the data, by the protection circuit identification, to provide the control circuit of the power supply to carry out a variety of protection measures. 3, the detection circuit to provide protection Circuit is running in a variety of parameters and a variety of instrumentation data. 4, auxiliary power supply to realize the power supply software (remote) start, for the protection circuit and control circuit (PWM and other chips) work power supply. 5 main classification editors in the field of switching power supply technology is the side of the development of related power electronic devices,?320W single-group switching power supply
side of the development of switching inverter technology, and the two promote each other to drive the switching power supply to two-digit annual growth rate. The switching power supply to more than double-digit annual growth rate toward the direction of light, small, thin, low noise, high reliability, anti-interference development. Switching power supply can be divided into two categories: AC/DC and DC/DC. Miniature low power switching power supply switching power supply is moving towards mass, miniaturization. Switching power supply will gradually replace the transformer in the life of all applications, low-power miniature switching power supply applications to be first reflected in the digital display meter, smart meters, cell phone chargers and so on. At this stage, the country is vigorously promoting the construction of smart grid, the requirements of the power meter greatly increased, switching power supply will gradually replace the transformer in the power meter above the application. The difference between inverting series switching power supply and general series switching power supply is that the output voltage of this inverting series switching power supply is negative voltage, which is exactly opposite to the positive voltage output of general series switching power supply; and because the energy storage inductor L only outputs the current to the load when the switch K is turned off, therefore, under the same conditions, the output current of inverting series switching power supply is higher than the output current of series switching power supply. Series switching power supply output current is twice as small.6 Development DirectionEditSwitching power supply high-frequency is the direction of its development, high-frequency switching power supply miniaturization, and switching power supply into a wider range of applications, especially in the field of high and new technology, promoting the development of switching power supply forward to more than two-digit growth rate per year in the direction of light, small, thin, low noise, high reliability, anti-interference Development. Switching power supply can be divided into two categories of AC / DC and DC / DC, DC / DC converter has now achieved modularity, and design technology and production processes at home and abroad have matured and standardized, and has been recognized by users, but the modularity of the AC / DC, because of its own characteristics make the process of modularity, encountered more complex technology and process manufacturing problems. In addition, the development and application of switching power supply is of great significance in energy saving, resource saving and environmental protection. Switching power supply in the application of power electronics devices are mainly diodes, IGBT and MOSFET, transformer. SCR in the switching power supply input rectifier circuit and soft start circuit has a small number of applications, GTR drive difficulties, low switching frequency, gradually replaced by IGBT and MOSFET. The development direction of switching power supply is high frequency, high reliability, low consumption, low noise, anti-interference and modularization.? Switching power supply
As switching power supply light, small, thin key technology is high frequency, so the major foreign switching power supply manufacturers are committed to the simultaneous development of new highly intelligent components, in particular, to improve the loss of the secondary rectifier parts, and increase scientific and technological innovation in the power ferrite materials to improve the high frequency and larger flux density (Bs) to obtain a high degree of magnetic performance, and the miniaturization of capacitors is also The application of SMT technology has led to significant progress in switching power supplies, where components are arranged on both sides of the circuit board to ensure that the switching power supply is light, small and thin. The high-frequency of switching power supply is bound to innovate the traditional PWM switching technology, and the soft-switching technology that realizes ZVS and ZCS has become the mainstream technology of switching power supply, and has greatly improved the efficiency of switching power supply. For high reliability indicators, the U.S. switching power supply manufacturers by reducing the operating current, reduce the junction temperature and other measures to reduce the stress of the device, making the reliability of the product greatly improved. Modular is the overall trend of the development of switching power supply, modular power supply can be used to form a distributed power supply system, can be designed as N +1 redundant power supply system, and to achieve capacity expansion in parallel mode. Switching power supply operation noise for this shortcoming, if the pursuit of high-frequency noise alone is bound to increase, and the use of part of the resonant conversion circuit technology, in theory, can achieve high-frequency and can reduce the noise, but part of the practical application of the resonant conversion technology is still a technical problem, it is still necessary to carry out a great deal of work in this field, in order to make the technology to be practical. The continuous innovation of power electronics technology, so that the switching power supply industry has a broad development prospects. To speed up the development of China's switching power supply industry, it is necessary to take the road of technological innovation, out of the joint development of production, learning and research with Chinese characteristics, to contribute to the rapid development of China's national economy.7 Working principle of editing switching power supply is quite easy to understand the process of switching power supply, in the linear power supply, so that the power transistors work in the linear mode, and linear power supply is different from PWM switching power supply is to let the power transistors work in the on and off mode, so that the power transistors work in the on and off mode. transistors to work in the on and off state, in both states, the volt-ampere product added to the power transistor is very small (in the on state, the voltage is low and the current is high; in the off state, the voltage is high and the current is small) / the volt-ampere product on the power device is the loss incurred on the power semiconductor device. Compared with linear power supply, PWM switching power supply is more efficient work process is through the "chopper", that is, the input DC voltage chopped into amplitude equal to the input voltage amplitude of the pulse voltage to realize.? Switching Power Supply Burt Diagram
The duty cycle of the pulses is regulated by the controller of the switching power supply. Once the input voltage is chopped into an AC square wave, its amplitude can be raised or lowered by a transformer. The output voltage can be increased by increasing the number of secondary windings in the transformer. Finally these AC waveforms are rectified and filtered to get the DC output voltage. The main purpose of the controller is to keep the output voltage stable and the process is very similar to the linear form of controller. This means that the functional blocks of the controller, the voltage reference and the error amplifier, can be designed to be the same as a linear regulator. Where they differ is that the output of the error amplifier (the error voltage) passes through a voltage/pulse width conversion unit before driving the power tubes. Switching power supplies have two main modes of operation: forward conversion and boost conversion. Despite the small difference in the arrangement of their parts, the working process varies greatly, and each has its own advantages in specific applications.8 Working conditionsEdit1、Switching: power electronics work in the switching state rather than the linear state2、High frequency: power electronics work in high frequency rather than low frequency close to the industrial frequency3、DC: switching power supply output is DC rather than AC9 Main featuresEdit1、Small size Light weight: because there is no industrial frequency transformer, so the volume and weight of only 20-30% of the linear power supply. 2, small power consumption, high efficiency: power transistors work in the switching state, so the power consumption on the transistor is small, the conversion efficiency is high, generally 60-70%, while the linear power supply is only 30-40%.10 mode of operation editor, as the name suggests, switching power supply is the use of electronic switching devices (such as transistors, field effect tubes, switching power supplies). transistors, field effect tubes, thyristors, etc.),? Switching power supply and circuit diagram
through the control circuit, so that the electronic switching device constantly "on" and "off", so that the electronic switching device on the input voltage pulse modulation, so as to realize the DC/AC, DC/DC voltage conversion, as well as the output voltage adjustable and automatic voltage regulation. DC/AC, DC/DC voltage conversion, and output voltage adjustable and automatic voltage stabilization. [1] Switching power supplies generally have three operating modes: fixed frequency and pulse width mode, fixed frequency and variable pulse width mode, and variable frequency and pulse width mode. The former mode of operation is mostly used for DC/AC inverter power supply, or DC/DC voltage conversion; the latter two modes of operation are mostly used for switching regulated power supply. In addition, the switching power supply output voltage also has three working modes: direct output voltage mode, average output voltage mode, amplitude output voltage mode. Similarly, the former mode of operation is mostly used for DC/AC inverter power supply, or DC/DC voltage conversion; the latter two modes of operation are mostly used for switching regulated power supply. According to the way the switching device is connected in the circuit, the more widely used switching power supply can be roughly divided into: series switching power supply, parallel switching power supply, transformer switching power supply and so on three categories. Among them, transformer-type switching power supply (later referred to as transformer switching power supply) can be further divided into: push-pull, half-bridge, full-bridge and other types; according to the excitation of the transformer and the phase of the output voltage, it can be divided into: forward excitation, flyback, single-excitation and double excitation, and other types; if from the use of the sub-division, it can also be divided into more types.11 Usage GuidelinesEditOutput CalculationBecause of the high efficiency of switching power supplies, generally up to 80% of the power supply, it is not easy to calculate the output voltage. High, generally can reach more than 80%, so in the selection of its output current, should be accurately measured or calculated the maximum absorption current of the power equipment, in order to be selected by the switching power supply has a high performance-price ratio, usually the output calculation formula: Is = KIf formula: Is - rated output current of the switching power supply; If - the maximum absorption current of the power equipment; K - the maximum absorption current of the power supply; K - the maximum absorption current of the power supply; K - the maximum absorption current of the power supply; K - the maximum absorption current of the switching power supply The maximum absorption current of the power-using equipment; K - margin factor, generally take 1.5 ~ 1.8; grounded switching power supply than the linear power supply will produce more interference, **** mode interference sensitive power-using equipment, grounding and shielding measures should be taken, according to the ICE1000, EN61000, FCC, and other EMC limitations, switching power supplies are to take the EMC electromagnetic compatibility measures, so the Switching power supplies should generally come with EMC EMC filters. For example, the HA series switching power supply of Leader HuaFu technology will connect its FG terminal to the earth or to the user's chassis in order to meet the above EMC requirements. Protection circuit switching power supply in the design must have overcurrent, overheating, short-circuit protection, etc., so in the design should be preferred to protect the full range of switching power supply module, and the technical parameters of its protection circuit should be matched with the operating characteristics of the power equipment, in order to avoid damage to the power equipment or switching power supply. Wiring method L: connected to 220v AC fire wire N: connected to 220v AC zero line FG: connected to the earth G: DC output of the ground +5v: output +5V point of the port ADJ: is within a certain range of adjustable output voltage, switching power supply on the output of the rated voltage was fixed at the time of factory, that is, the nominal rated output voltage, set the potentiometer allows the user to adjust the output voltage according to the actual use of a smaller range, generally, the output voltage is adjusted within the scope of the switching power supply. Setting this potentiometer allows the user to adjust the output voltage according to the actual use of a smaller range, in general there is no need to adjust it.12 Maintenance Methods Editorial Maintenance Steps 1, repair the switching power supply, first of all, use a multimeter to detect whether the power components are short-circuited,? Switching power supply shell
such as power rectifier bridge stack, switching tubes, high-frequency high-power rectifier tubes; inhibit the surge current of high-power resistors are burned out. Then test each output voltage port resistance is abnormal, the above components need to be replaced if they are damaged.2, the first step is completed, after turning on the power supply can not work properly, then to test the power factor module (PFC) and pulse width modulation components (PWM), consult the relevant information, familiar with the function of each leg of the PFC and PWM module and its module to work properly the necessary conditions.3, and then for the power supply with a 3, then, for the power supply with PFC circuit, you need to measure the filter capacitor voltage is about 380VDC, if there is a voltage of about 380VDC, indicating that the PFC module is working properly, and then detect the PWM components of the working state, measure the power input VC, the reference voltage output VR, the start control Vstart/Vcontrol terminal voltage is normal, the use of 220VAC / 220VAC isolation transformer to the pulse width modulation module (PWM). 220VAC isolation transformer to the switching power supply, using an oscilloscope to observe the PWM module CT terminal to ground waveform is a good linear sawtooth wave or triangle, such as the TL494 CT terminal for the sawtooth wave, FA5310 CT terminal for the triangle wave. Whether the waveform of the output terminal V0 is an orderly narrow pulse signal.4. In the switching power supply maintenance practice, there are many switching power supply using UC38×× series 8-pin PWM components,? Switching Power Adapter
Most power supplies do not work because the power supply startup resistor is damaged, or the chip performance is degraded. When R is broken no VC, PWM component can not work, need to replace the resistor with the same value as the original power resistance. When the PWM component startup current increases, the R value can be reduced until the PWM component can work normally. In the repair of a GE DR power supply, PWM module for the UC3843, testing did not find any other abnormalities in the R (220K) on the parallel connection of a 220K resistor, PWM components work, the output voltage are normal. Sometimes due to peripheral circuit failure, resulting in the VR terminal 5V voltage of 0V, PWM components do not work, in the repair of the Kodak 8900 camera power supply, encountered this situation, and the VR terminal connected to the external circuit is disconnected, the VR from 0V to 5V, the PWM components work normally, the output voltage is normal. 5, when the filter capacitor on the voltage of 380VDC or so, indicating that the PFC circuit does not work properly,? The PFC circuit is not working properly,
? Switching power supply circuit schematic
PFC module key detection feet for power input feet VC, start feet Vstart/control, CT and RT feet and V0 feet. Repair a Fuji 3000 camera, test a board on the filter capacitor without 380VDC voltage. vc, Vstart/control, CT and RT waveforms and V0 waveforms are normal, measurement of the field effect power switching tube G-pole no V0 waveforms, due to the FA5331 (PFC) for the SMD components, the machine used for a long time after the V0 end of the board with the virtual weld between the V0 signal is not sent to the field effect tube G-pole. V0 signal is not sent to the G pole of the field effect tube. The V0 end and the board soldering points welded, using a multimeter to measure the filter capacitor has 380VDC voltage. When the Vstart/control end is low, the PFC can not work, it is necessary to test its endpoints and peripheral connected to the relevant circuit. In short, the switching power supply circuit is easy and difficult, the power has a large and small, a variety of output voltages. As long as you grasp the core of things, that is, fully familiar with the basic structure of the switching power supply and the characteristics of the PFC and PWM module, the basic conditions of their work, in accordance with the above steps and methods, more hands-on switching power supply maintenance, you can quickly troubleshooting switching power supply to achieve twice the result with half the effort. Maintenance techniques switching power supply maintenance can be divided into two steps: power failure, "look, smell, ask, measure" look: open the shell of the power supply, check whether the fuse is blown, and then observe the internal situation of the power supply, if the power supply is found to have a burnt place on the PCB board or components rupture, should focus on checking the components here and the related circuit components. Asset Management Smell: Smell the inside of the power supply to see if there is a pasty odor and check if there are burnt components. Ask: Ask how the power supply was damaged, and whether the power supply has been operated in violation of the law. Measure: Before not energized, use a multimeter to measure the voltage at both ends of the high-voltage capacitor first. If the switching power supply does not vibrate or switching tube open-circuit caused by the failure, the majority of cases, the high-voltage filter capacitor voltage on both sides of the discharge has not been eulogized, this voltage is more than 300 volts, need to be careful. Use a multimeter to measure the positive and negative resistance and capacitor charging at both ends of the AC power line, the resistance value should not be too low, otherwise there may be a short circuit inside the power supply. Capacitors should be able to charge and discharge. Disconnect the load, respectively, measure the resistance of each group of outputs to ground, when normal, the needle should be capacitor charging and discharging swing, the last indication should be the resistance value of the discharge resistance of the road. Power detection after power on to observe whether the power supply has burned insurance and individual components smoke and other phenomena, if any to cut off the power supply in time for maintenance. Measure the high pressure filter capacitor ends with or without 300 volts output, if not should focus on checking the rectifier diode, filter capacitor. Measure the high-frequency transformer secondary coil output, if not should focus on checking whether the switching tube is damaged, whether the vibration, whether the protection circuit action, etc., if there should focus on checking the output side of the rectifier diode, filter capacitors, three-pass regulator, etc.. If the power supply starts and stops, the power supply is under protection, you can directly measure the voltage of the protection input pin of the PWM chip, if the voltage exceeds the specified value, it means that the power supply is under protection, and you should focus on checking the reasons for the production of the protection.13 Precautions 1, the selection of the switching power supply should be taken into account when 1) selecting the appropriate specifications of the input voltage; 2) selecting the appropriate power. In order to make the life of the power supply grow, you can choose 30% more output power rated models. 3) Consider the load characteristics. If the load is a motor, light bulb or capacitive load, the current is higher when the power is turned on instantly, so you should choose the right power supply to avoid overload. If the load is a motor, you should consider the voltage back-up during shutdown. 4) In addition, you need to consider the operating temperature of the power supply and whether there is additional auxiliary cooling equipment, the power supply needs to be derated at too high a ring temperature output. (5) According to the application of the required selection of functions: protection functions: over-voltage protection (OVP), over-temperature protection (OTP), over-load protection (OLP) and so on. Application functions: signal function (normal power supply, power supply failure), remote control function, telemetry function, parallel connection function, etc. Special Functions: Power Factor Correction (PFC), Uninterruptible Power Supply (UPS) 6) Select the required safety regulations and electromagnetic compatibility (EMC) certification. 2, the use of switching power supply precautions 1) before using the power supply to determine the input and output voltage specifications and the power supply used to determine whether the nominal value of the match; 2) before the power supply to check the input and output wires are connected correctly, so as to avoid damage to the user's equipment; 3) check whether the installation is secure, the mounting screws and the power supply with a nominal value; 3) check the power supply to ensure that the power supply is installed correctly. Installation is firm, mounting screws and power board devices have no contact, measure the insulation resistance of the shell and input, output, in order to avoid electric shock; 4) In order to ensure the safety of use and reduce interference, please ensure that the ground terminal is reliably grounded; 5) Multiple output power supply is generally divided into main and auxiliary outputs, the main output characteristics are better than the auxiliary outputs, the main output of a large output current in general. In order to ensure that the output load adjustment rate and output dynamics and other indicators, generally require each road at least 10% of the load. If you use the auxiliary circuit without the main circuit, the main circuit must be added to the appropriate dummy load. Specifically, see the corresponding model specifications; 6) Please note: Power frequent switching will affect its life; 7) The working environment and the degree of load will also affect its life.