A strategic control scheme of phase-shift full bridge converter for improving light-load efficiency in server power system

Abstract

The phase-shifted full bridge (PSFB) converter is widely used in the middle and high power applications such as a server power system. However, due to the newly required trend for high light-load efficiency, the PSFB converter has a limitation for light-load efficiency because of a large circulating current, core losses of the transformer and inductors, and the insufficiency ZVS energy of lagging-leg switches. To achieve high light-load efficiency in PSFB converter, the circulating current in the freewheeling mode and the core loss should be reduced. Therefore, this paper proposes the strategic control scheme employing the control scheme of the two-switch forward (TSF) converter. In addition, by applying the additional one gate signal and the expanded dead-time, the switching loss can be significantly reduced. To verify the proposed method, the prototype converter with 750W (12V/62.5A) is built and tested.