A practical comparison of high frequency off-line power converter topologies

Three half-bridge power converters, employing resonant techniques to shape the high-frequency switching waveforms, are compared for offline 12 V, 10 A output applications. The operation of the zero-current- and zero-voltage-switched quasi-resonant converters is reviewed, along with that of the parallel resonant converter. Particular attention is paid to the distribution of the resonant inductance around the transformer. Each converter is designed to operate at a similar switching frequency under full-load, low-line conditions. A loss analysis is carried out for each converter, and suggestions for improving the efficiency are made. The three topologies are breadboarded and the practical results evaluated. Waveforms are provided and discussed for each circuit at full load. The zero-current-switched quasi-resonant converter is identified as the circuit capable of offering the highest power density for a given maximum power dissipation.<>