Main types of switching power supply
There are two types of modern switching power supplies: one is DC switching power supply; the other is AC switching power supply.
Internal structure of switching power supply
The main introduction here is only the DC switching power supply, whose function is to convert the original ecological power supply (rough power) with poor power quality, such as mains power supply or battery power supply, into a high-quality DC voltage (fine power) that meets the requirements of the equipment. . The core of the DC switching power supply is the DC/DC converter. Therefore, the classification of DC switching power supplies is based on the classification of DC/DC converters. That is to say, the classification of DC switching power supply is basically the same as that of DC/DC converter, and the classification of DC/DC converter is basically the classification of DC switching power supply.
DC/DC converters can be divided into two categories according to whether there is electrical isolation between the input and output: one is isolated DC/DC converters; the other is non-isolated DC/DC converters. DC/DC converter.
Isolated DC/DC converters can also be classified by the number of active power devices. There are two types of single-tube DC/DC converters: Forward and Flyback. Double-tube DC/DC converters include DoubleTransistor Forward Converter, Double Transistr Flyback Converter, Push-Pull Converter and Half-Bridge Converter. four. The four-tube DC/DC converter is a full-bridge DC/DC converter (Full-Bridge Converter).
According to the number of active power devices, non-isolated DC/DC converters can be divided into three types: single-tube, dual-tube and quad-tube. Internal structure of switching power supply
There are six types of single-tube DC/DC converters, namely Buck DC/DC converter, Boost DC/DC converter, Buck Boost DC/DC converter , Cuk DC/DC Converters, Zeta DC/DC Converters and SEPIC DC/DC Converters. Among these six single-tube DC/DC converters, Buck and Boost DC/DC converters are the basic ones, and Buck-Boost, Cuk, Zeta, SEPIC DC/DC converters are derived from them. The double-tube DC/DC converter has a double-tube series-connected boost (Buck-Boost) DC/DC converter. The commonly used four-tube DC/DC converter is a full-bridge DC/DC converter (Full-Bridge Converter).
When the isolated DC/DC converter realizes the electrical isolation between the output and the input, it is usually realized by a transformer. Because the transformer has the function of transforming the voltage, it is beneficial to expand the output application range of the converter, and it is also convenient to realize multiple outputs of different voltages. , or multiple outputs of the same voltage.
When the voltage and current ratings of the power switches are the same, the output power of the converter is usually proportional to the number of switches used. Therefore, the more the number of switches, the greater the output power of the DC/DC converter. The output power of the four-tube type is twice that of the two-tube type, and the output power of the single-tube type is only 1/4 of the four-tube type.
The combination of non-isolated converters and isolated converters can achieve some characteristics that a single converter does not have.
According to the transmission of energy, there are two types of DC/DC converters: one-way transmission and two-way transmission. A DC/DC converter with bidirectional transmission function can transmit power from the power supply side to the load side, and can also transmit power from the load side to the power supply side.
DC/DC converters can also be divided into self-excited and separately controlled. A converter that realizes the self-sustained periodic switching of the switch tube by means of the positive feedback signal of the converter itself is called a self-excited converter, such as a Royer converter, which is a typical push-pull self-excited converter. The switching device control signal in the separately controlled DC/DC converter is generated by an external special control circuit.
According to the switching conditions of the switching tube, the DC/DC converter can be divided into two types: hard switching (Hard Switching) switching power supply and soft switching (Soft Switching). The switching device of the hard-switching DC/DC converter turns on or off the circuit under the condition of withstand voltage or current, so a large overlap loss will be generated during the turn-on or turn-off process, the so-called Switching loss (Switching loss). When the working state of the converter is constant, the switching loss is also constant, and the higher the switching frequency, the greater the switching loss. At the same time, during the switching process, the circuit distributed inductance and parasitic capacitance will oscillate, resulting in additional losses. Therefore, The switching frequency of a hard-switched DC/DC converter cannot be too high. The switch tube of the soft-switching DC/DC converter, during the turn-on or turn-off process, or the voltage applied to it is zero, that is, zero-voltage switching (Zero-Voltage-Switching, ZVS), or through the switch tube. The current is zero, that is, zero-current switching (Zero-Current·Switching, ZCS). This soft switching method can significantly reduce the switching loss and the oscillation caused during the switching process, so that the switching frequency can be greatly increased, creating conditions for the miniaturization and modularization of the converter. Power field effect transistor (MOSFET) is a switching device that is widely used. It has a high switching speed, but also has a large parasitic capacitance. When it is turned off, under the action of external voltage, its parasitic capacitance is fully charged. If this part of the charge is not discharged before it is turned on, it will be consumed inside the device, which is the capacitive turn-on loss. In order to reduce or eliminate this loss, the power field effect transistor should adopt the zero-voltage turn-on mode (ZVS). Insulated Gate Bipolar Transistor (IGBT) is a composite switching device. The current tailing during turn-off will cause a large turn-off loss. If the current flowing through it is reduced to If it is zero, the switching loss can be significantly reduced, so the IGBT should be turned off by zero current (ZCS). Turning off the IGBT under zero voltage conditions can also reduce the turn-off loss, but when the MOSFET is turned on under zero current conditions, the capacitive turn-on loss cannot be reduced. Resonant Converter (ResonantConverter, RC), Quasi-Resonant Converter (Qunsi-Tesonant Converter, QRC), Multi-Resonant Converter (Mu1ti-ResonantConverter, MRC), Zero Voltage Switching PWM Converter (ZVS PWM Converter), Zero Current Switching PWM Converter (ZCS PWM Converter), zero voltage conversion (Zero-Vo1tage-Transition, ZVT) PWM converter and zero-current conversion (Zero-Vo1tage-Transition, ZVT) PWM converter, etc., all belong to soft switching DC converters. The development of power electronic switching devices and zero-switching converter technology has prompted the development of high-frequency switching power supplies.
Main types of switching power supply