A Pre Turn-off Circuit for Synchronous Rectification Controller of Flyback Converter

This paper presents a pre turn-off circuit that can reduce the pull-down time of secondary rectifier in synchronous rectification controller of flyback converter. By detecting the drain-to-source voltage of secondary rectifier, it can control the gate driving voltage to a lower value so that it can turn off the rectifier quickly. The proposed circuit has been implemented in nuvoton 0.35um BCD process. The simulation result shows that it can apparently reduce the pull-down time. When the driving voltage is lower than 15V, it can save about 70% of pull-down time with 90uW power consumption.