Design Of Zero Voltage Switching Symmetrical Half Bridge DC-DC Converter

Traditional symmetrical half bridge circuit with simple structure, good controlperformance and the ability of magnetic bias restriction is widely adopted in theinverter welding supply. The disadvantages of the traditional half bridge are that it isnot soft switching and there is resonance caused by the leakage of the transformer andthe junction capacitances of the switches in it when the two switches are off. Theserestrict the improvements of the frequency and the performance of the inverterwelding machine. To solve these problems a zero voltage switching (ZVS)symmetrical DC-DC converter is proposed.An auxiliary circuit including two series-opposing switches is inserted across themidpoints of the input power source and the half-bridge based on the traditionalhalf-bridge converter. The oscillation caused by the parasitic parameters can beeliminated and all power switches can achieve ZVS in the proposed converter. Thedriving signals of the main transistors are same as those of the traditional half-bridgeconverter. The driving signals of the auxiliary transistors are delayed by the drivingsignals of the main transistors. Traditional modulation chip such as SG3525can beapplied in the proposed converter, which facilitates the control circuit.This paper analyzes the operation principle of the proposed ZVS symmetricalhalf-bridge converter. Equivalent circuit and its equation of each period of theconverter are created. The characteristics of the proposed ZVS symmetrical half-bridge converter is considered. The ZVS requirement is derived from the equations ofthe circuit. The parameters in this converter are designed and the ac small signalcircuit is created for the loop control. Traditional pulse width control chip is used forthe control of the converter. A method of digital control is also given in this paper.The inverter welding machine adopts power module as its switches, so this paperanalyzes the application of the power modules in the ZVS symmetrical half-bridge andprovides a reference to the design of the power module. Finally, an800w prototype is designed for experiments. The traditionalsymmetrical half bridge converter and the ZVS symmetrical half bridge are bothexperimented based on the same prototype and their efficiency curves are given. Theresults of the experiments confirm the proposed converter is valid. It is practical forthe inverter welding machine.