Synchronous Rectifier Control Algorithm to Improve Efficiency of Full-Bridge Converter with Asymmetric PWM Control

This paper presents the novel switching control method for synchronous rectifier with the asymmetric pulse-width-modulation (APWM) controlled full-bridge converter. Differently from the phase-shift control, the diagonally-located switches in the input-side of full-bridge converter operate simultaneously with the APWM method. If it operates in continuous current mode (CCM), the synchronous rectifier can be easily controlled with the OR-gated signal control method, which is conventionally used as the driving technique for synchronous rectifier with the phase-shifted control. However, the current flowing through the body diode of switches in synchronous rectifier still exists. In addition, the OR-gated signal control method results in the huge increase of total loss in discontinuous current mode (DCM) because of reverse currents flowing through channels of rectifier-side switches. In this paper, the switching control signals for synchronous rectifier are analyzed in both CCM and DCM to minimize total switch loss. Also, their boundary condition is mathematically analyzed. In summary, the new switching controller for synchronous rectifier is proposed, and its performance is evaluated by the PSIM simulation.