A Simple Switching Control Technique for Improving Light Load Efficiency in a Phase-Shifted Full-Bridge Converter with a Server Power System

In phase-shifted full-bridge (PSFB) converter, using discontinuous conduction mode (DCM) is one of the most effective ways to improve efficiency in the light load condition. DCM of the PSFB converter allows getting reduced the duty ratio and zero voltage switching (ZVS) in the light load condition. Because of its simplicity, commercial IC adapted DCM by turning-off synchronous rectifiers (SRs). However, turning-off SRs causes large conduction losses in body diodes of SRs, and ZVS condition or optimized dead time are not defined yet. This letter proposes to use “AND-gated” control signals for SRs to reduce conduction losses in body diodes. Also, the ZVS condition is presented to design dead time easily. The feasibility of the proposed technique has been verified with 90-265 Vac input, 400 V link voltage, and 12V/750 W output server computer power supply system.