Active-clamp ZVS converter with step-up voltage conversion ratio

This paper presents a new isolated dc/dc converter with zero-voltage turn-on switching (ZVS) of power switches and zero-current turn-off switching (ZCS) of diodes. In conventional flyback converter, the main drawbacks are high voltage stresses on power devices large transformer size, and serious reverse recovery current which resulted in high voltage spike across output diode. To solve these problems, buck-boost type of active-clamp circuit is connected in parallel with the primary winding to clamp the voltage spike across the power switch, recycle the energy stored in the leakage and magnetizing inductances of transformer and realize the turn-on ZVS by utilizing the leakage inductance and output capacitance of switch. The leakage inductance and the resonant capacitance on the secondary side are resonant to allow the output diodes turn-off at ZCS. Thus the switching losses and thermal stresses of the switches and diodes are reduced, the output diode has no reverse recovery problem, and voltage stresses of the output diodes are clamped to the output voltage. Experiments conducted on a laboratory prototype rated at 270 W are provided to verify the effectiveness of the proposed converter.