An improved driving method for synchronous rectifier using drain-source voltage sensing

Traditional voltage sensing method has already been widely used for the synchronous rectifier. However, the parasitic parameters will cause the false turn-on and early turn-off problem. In this paper, the conception of zero-crossing noise filter is presented. By applying this filter to the synchronous rectifier, the false turn-on and early turnoff problem can be resolved. Only three passive components are needed in the proposed filter which makes it reliable and easy to implement. Simulation and experimental results show that the zero-crossing noise filter can significantly improve the reliability as well as the efficiency of the power circuit. A 400V to 12V 100W Flyback converter and a 600W half bridge LLC resonant converter prototype are built to verify the advantages of the new zero-crossing noise filter.