Open loop synchronous rectifier driver for LLC resonant converter

Synchronous rectifier (SR) is widely used in LLC resonant converter to reduce the conduction loss. Due to different operation modes, the SR control is complicated and increases system cost. In this paper, based on the observation on LLC diode conduction time, an open-loop fixed-on-time SR driving method is proposed. The optimal on-time is used to control the SR to simplify the implementation in different operation mode and reduce the system cost while maintains large efficiency improvement. The total efficiency of LLC resonant converter with SR driven by the proposed scheme is proved to increase by 2% under different load conditions with minimum system cost.