Implementation of a zero voltage switching DC/DC converter with three buck-type active clamp circuits

This study presents a new parallel forward converter with low voltage stress of MOSFETs. The buck-type of the active clamp topology is used to reduce the voltage stress of MOSFET. The stacked half-bridge converter with three asymmetric pulse-width modulation (PWM) circuits is adopted to reduce the power rating of power MOSFETs, transformers, rectifier diodes and the output inductors. Based on the asymmetric PWM scheme, power MOSFETs can be turned on with zero voltage because of the resonant behaviour during the transition interval. Two half-bridge circuits are used at the high voltage side to reduce the voltage stress of each MOSFET at one-half of the input voltage. Thus the MOSFETs with 500 V voltage stress can be used at the 1000 V input voltage case. Three asymmetric PWM circuits are parallel-connected at the low voltage side to achieve the load current sharing and to reduce the current rating of each magnetic component and the rectifier diode. Thus the size of the output chokes and capacitor are reduced. Finally, experiments based on a laboratory prototype with a rated 1 kW are provided to demonstrate the performance of proposed converter.