A New Control for Synchronous Rectifier of Phase-Shifted Full-Bridge Converter to Improve Efficiency in Light-Load Condition

This article proposes a new control method for the synchronous rectifier (SR) of phase-shifted full-bridge (PSFB) converter to improve its efficiency in light-load condition. In general, the PSFB converter operates in the discontinuous conduction mode (DCM) in light-load condition to reduce the effective duty-ratio and core loss. However, the conventional control methods in the DCM cause undesirable conduction loss in SR because the output inductor current flows through the body-diode instead of the channel of SR. To figure it out, the proposed control method modulates the turn-on time of SR to eliminate the body-diode conduction. Moreover, it can be easily implemented without any auxiliary circuits. Therefore, it can improve the efficiency in light-load condition while keeping the advantages of DCM. The operating principle of PSFB converter in the DCM is first described. Thereafter, the proposed control method for SR is theoretically analyzed. Finally, its practical effectiveness is verified by experimental tests on the hardware implementation.