(A) new zero-voltage switching half-bridge converter with reduced rectifier voltage ringing

Abstract

Symmetric half bridge converter has been widely used in PC power supply application since it has no DC offset of magnetizing current and it has symmetric device stress. However, symmetric half bridge is not suitable for PC power supply application which should satisfy hold-up time requirement. When operating at below 0.5 duty ratio, symmetric half bridge cannot achieve zero-voltage switching (ZVS). It results in low efficiency. To solve this problem, a variety of ZVS half bridge converters have been proposed including an asymmetric half bridge converter. Though they can reduce switching loss, ZVS half bridge converters have serious voltage oscillation problem across the secondary rectifier, which would require the snubber circuit. This oscillation is increasingly severe when large resonant inductance is used for wide ZVS range. The proposed converter solves this problem by separating resonant inductance from resonance with the junction capacitance of the rectifier after a commutation. It reduces energy dissipation on snubber and decreases conduction loss on rectifier. In addition, it has wide ZVS range resulting in improving efficiency. Operational principle and analysis of the proposed converter are presented and confirmed by experimental results of a 240W prototype.