A novel quasi-resonant ZVZCS phase shift full bridge converter with an active clamp in the secondary

An active clamp circuit is one of the effective solutions to reduce circulating current and to damp the voltage ringing across the secondary rectifier in the conventional phase-shift full-bridge converter. Though many kinds of active clamping circuits have been proposed so far, most of them still suffer from hard switching of the primary leading leg switches and the active clamp switch which degrades the overall efficiency of the converter. In this paper a novel hybrid PWM quasi-resonant active clamp phase-shifted full-bridge is presented and analyzed. The clamping capacitor is selected to resonate with the leakage inductance of transformer and the active clamp switch is controlled properly to achieve ZCS turn-off of all the primary switches. The proposed converter can offer additional advantages such as ZVS turn-on for all the primary switches regardless of the load, elimination of the reverse recovery problem of diode, and soft-switching turn-on of the active clamp switch. To validate its performance, a 3.5 kW prototype was built and tested with 380V input and 250–420V output.