Synchronous rectifier (SR) is widely adopted in flyback converter to reduce the conduction loss. However, the conventional SR driving method based on direct current or voltage sensing is sensitive to the parasitic ring, which may cause SR early turn off and therefore decrease the converter efficiency. This innovation presents a novel SR driving method to avoid the impact of parasitic ringing by adding an simple RC network. The RC network senses the voltage across SR and generates a very clean waveform which is similar to the magnetizing current waveform. SR signal could be easily generated based on the clean waveform and the time sequence could be very accurate. Therefore, the converter efficiency could be optimized.