The Research On Soft Switching Technology Of DC/DC Converter

In recent years switching power supply is developing toward miniaturization direction. With the increase of switching frequency, switching loss becomes the main loss in the circuit. Soft switch technology is the effective way to solve switching loss. Passive lossless soft switching technology can simple, and has lower cost and higher reliability, so it has been widely used for its practicality.In this paper, we summarize the development and status of DC-DC converter soft switch technology. From the basic idea of soft switching, we discuss the basic principle and circuit topology of active soft switching technology and passive soft switching technology.In this paper, according to the design principles of passive lossless soft switch circuit,we design minimum voltage stress passive lossless snubber circuit,non-minimum voltage stress passive lossless snubber circuit and minimum stress passive lossless snubber circuit based on Buck circuit. After theoretical analysis, we analysis the circuit stages, give the realization conditions of soft switching and design principles of parameter.In the soft switching working process minimum voltage stress passive lossless snubber circuit will not increase voltage stress of main switch. Because of the working mode, ratio of snubber inductance and capacitance is restricted, thus the duty cycle range is limited. Non-minimum voltage stress passive lossless snubber circuit will increase the voltage stress of main switch, but it can reduce the current rising rate by adding an inductance, and the restriction of inductance and capacitance ratio is disappear. It can achieve wider duty cycle range. Minimum stress passive lossless snubber circuit solves the shortages of the two circuits above, it has minimum voltage stress on the main switch, and the incremental of current stress is also very small.The proposed passive lossless snubber circuits are simulated by Simulink software, the simulation results show that three kinds of circuits can achieve zero current open and zero voltage shut off. In this paper we build a 1kW experimental platform of non-minimum voltage stress passive lossless snubber circuit. The experimental results indicate that the passive lossless soft switching technology can reduce switching loss,du/dt,di/dt and electromagnetic interference EMI.