A single-switched high-switching-frequency quasi-resonant flyback converter with zero-current-switching and valley-switching

In The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. In this paper, a high-switching-frequency single-switched quasi-resonant flyback converter that features low switching loss and low switching noise is proposed. A resonant inductor of primary side and a resonant capacitor of secondary side are utilized to recycle the transformer leakage energy and realize zero-current-switching (ZCS) at turn-off and valley-switching (VS) at turn-on of the primary switch, and ZCS turn-off of diode. The VS is realized based on the resonance between the resonant inductor and the equivalent switch drain capacitor which helps to realize near fully soft switching. Compared to traditional quasi-resonant converters, the switching loss is greatly reduced. And low cost, low losses and low switching noise are all acquired. The proposed concept has been validated on a 1MHz 12V/3A prototype with 80V dc input. The peak efficiency is 90.4% using GaN device without synchronous rectification in the open loop test.