Synchronous Bridge Rectifier for MHz Resonant Converter Based on Digital Control

This paper presents the development of a general MHz synchronous rectifier (SR) designed for resonant converters. It examines the potential losses in a non-ideal SR, encompassing driving losses, conduction losses, switching losses, and body-diode losses. When employing the drain-source voltage for synchronization, it investigates the signal delay and mismatch introduced by detector, driver and transistor parasitic to elucidate the challenges faced by a digital controller. To address these issues, this paper proposes a fast synchronous phase control coupled with a slow adaptive dead-time control to dynamically modulate the driving signal. Experimentally, it implemented and tested a 60-W, 6.78-MHz rectifier in a wireless charger. The synchronous rectifier achieved a peak efficiency of 97.7%, ensuring at least a 5.0% efficiency improvement compared to a passive rectifier.