Evaluation and design of megahertz-frequency off-line zero-current-switched quasi-resonant converters

A performance comparison of flyback, forward, and half-bridge zero-current-switched quasi-resonant converter topologies for high-frequency offline applications is presented. It is shown that the half-bridge topology with secondary side resonance operating in half-wave mode is most suitable. A complete design procedure for the half-bridge power stage and the voltage-feedback control is presented together with experimental results for a 300 V DC hybridized converter which operates with conversion frequencies from 400 kHz to 2 MHz and delivers 1.5-16 A at 5 V DC.