Patent ID: 8004862

Claim:
A synchronous rectifying circuit of soft switching power converter with a transformer, comprising: a current transformer generating a switching-current signal in response to the switching of the transformer; and an integrated synchronous rectifier comprising: a power transistor coupled to the transformer and an output of the power converter for the rectifying; and a controller generating a drive signal to control the power transistor directly in response to the switching-current signal; wherein the controller generates a start signal when the switching-current signal is higher than a first threshold; the controller generates a stop signal when the switching-current signal is lower than a second threshold; the start signal is coupled to enable the drive signal to turn on the power transistor; the stop signal is coupled to disable the drive signal to turn off the power transistor; wherein the controller comprises a pulse-width detection circuit generating an integration signal, a ramp signal and a pulse signal; wherein the integration signal is generated in accordance with a period between the start signal and the stop signal, the ramp signal is generated in response to the start signal, the pulse signal is generated by comparing the integration signal and the ramp signal to disable the driver signal and turn off the power transistor.