The DC/DC converter can be divided into two types: hard switching and Soft Switching. The switching device of the hard switching DC/DC converter is opened or turned off the circuit when the voltage or flowing through the current. Therefore, during the opening or turning process Switch loss. When the working status of the converter is certain, the switching loss is also certain, and the higher the switching frequency, the greater the switching loss. At the same time, the oscillation of the circuit distribution inductance and parasitic capacitance will be aroused during the switching process, which brings additional losses. The switching frequency of the hard switching DC/DC converter should not be too high. The switch of the soft switch DC/DC converter, during the opening or turning process, or the voltage added to it is zero, that is, the zero-voltage-switching (ZVS), or through the switch tube tube The current is zero, that is, the zero-current · switching (ZCS).  
 
This soft switching method can significantly reduce the switching loss and the oscillating stirred during the switching process, so that the switching frequency can be greatly improved, creating conditions for the miniaturization and modularization of the converter. The power field effect tube (MOSFET) is a switching device with more applications. It has a higher switching speed, but it also has a large parasitic capacitor. When it turns off, its parasitic capacitor is fully charged under the action of external voltage. If this part of the charge is not released before it is opened, it is consumed inside the device. This is the loss of the capacity of the capacity. In order to reduce or eliminate this loss, the power field effect tube should be used in zero voltage opening (ZVS). Insulating Gated Gate Bipolar Tansistor (IGBT) is a composite switch device. The current trailer at the time of cutting will cause a large turnover loss. Zero can significantly reduce the switching loss, so IGBT should use zero current (ZCS) to turn off.  
 
IGBT can also reduce the loss loss at zero voltage conditions, but when MOSFET is opened under zero current conditions, it cannot reduce the losses of the capacity opening. Resonant converter (RC), quasible resonance converter (QRC), Multi-ResonantConverter, MRC), zero-voltage switch (ZVS PWM Converter), zero-current switch PWM The converter (ZCS PWM Converter), Zero-Voltage-Transitation (ZVT) PWM converter and zero-current conversion (ZERO-VOLTAGE-TRANSITION, ZVT) PWM converter, all belong to the soft switch DC converter. The development of electronic electronic switching devices and zero -switch converters has promoted the development of high -frequency switching power supply.