Patent ID: 8154888

Claim:
A synchronous rectifier circuit of a switching power converter, comprising: a power transistor and a diode coupled to a transformer and an output of the switching power converter for rectifying; a controller generating a drive signal to control the power transistor in response to an on signal and an off signal; and a phase-lock circuit generating the off signal in accordance with the on signal; wherein the on signal is enabled once the diode is forward biased; and wherein the on signal is coupled to enable the drive signal for turning on the power transistor, and the off signal is coupled to disable the drive signal for turning off the power transistor; wherein the phase-lock circuit comprises: a charging circuit generating a ramp signal when the on signal is enabled; and a sampled circuit generating a hold signal in accordance with the level of the ramp signal; a comparator generating the off signal in response to comparison of the ramp signal and the hold signal; wherein the level of the hold signal is correlated to the period of the on signal.