Analysis and implementation of an active-clamping zero-voltage turn-on switching/zero-current turn-off switching converter

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 is presented. In conventional flyback converters, the main drawbacks are high voltage stresses on power devices, large transformer size and serious reverse recovery current, which resulted in high voltage spikes across output diode. To solve these problems, a buck-boost type of active-clamp circuit is connected in parallel with the primary winding to clamp the voltage spike across the power switch, to recycle the energy stored in the leakage and magnetising inductances of the transformer and to realise the turn-on ZVS by utilising the leakage inductance and output capacitance of the switch. The leakage inductance and the resonant capacitance on the secondary side are resonant to allow the output diodes to turn off at ZCS. Thus, the switching losses and thermal stresses of 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.