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

Symmetric half-bridge (SHB) 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, it is difficult for SHB converter to get high efficiency due to significant switching loss. To solve this problem, a variety of Zero-Voltage Switching (ZVS) half-bridge converters have been proposed including an asymmetric half-bridge (AHB) converter. They can reduce switching loss with ZVS. However, 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 for ZVS from resonance with the rectifier junction capacitance. It reduces energy dissipation on snubber and decreases conduction loss on rectifier. In addition, it has wide ZVS range with series-connection of main switches. Operational principle and analysis of the proposed converter are presented and confirmed by experimental results of a 240W prototype.