A synchronous rectifying circuit is provided for power converter. A pulse signal generator is utilized to generate a pulse signal in response to the leading edge and the trailing edge of a switching signal. The switching signal is used for switching the transformer of the power converter. An isolation device such as pulse transformer or small capacitors is coupled to the pulse signal generator for transferring the pulse signal through an isolation barrier of a transformer. A synchronous rectifier includes a power switch and a control circuit. The power switch is equipped in between the secondary side of the transformer and the output of the power converter for the rectifying. The control circuit having a latch is operated to receive the pulse signal for turning on/off the power switch.