Synchronous Rectification Using Resonant Capacitor Voltage for Secondary Side Resonant Active Clamp Flyback Converter

Secondary side resonant active clamp flyback (SSR-ACF) converter is a better candidate than primary side resonant active clamp flyback (PSR-ACF) converter to be used in high frequency small power supply applications. Based on the resonant capacitor voltage in SSR-ACF converter, this paper proposes an accurate synchronous rectification (SR) control method to turn off the synchronous rectifier (SRer) at the right point. Compared with the current widely used SR detecting method, the turn off point of SRer based on the presented method can not be affect by noise or voltage oscillation, and not need complicated sensing circuit. To verify the proposed SR control method, the simulation and experimental results of a 65w 19.5v output SSR-ACF converter are given. The results show that the SRer can be switched off at the right point by the proposed method. Compared with the current widely used SR detecting method, the efficiency in heavy load is improved by 0.3%.