Patent ID: 8054656

Claim:
A switching control circuit for a switching power converter, the switching control circuit being coupled to a switching device and an auxiliary winding of a transformer, and a primary winding of the transformer being coupled to the switching device, wherein the switching control circuit comprises: a voltage receiver, comprising: a switch coupled to the auxiliary winding of the transformer through a resistor for receiving a reflected voltage signal from the resistor, the reflected voltage being proportional to a voltage across the switching device when the switching device is turned off; a first current mirror coupled to the switch for transforming a first current flowing through the switch into a second current; and a sampling resistor coupled to the first current mirror for receiving the second current and generating a peak voltage signal; a comparing unit coupled to the voltage receiver for receiving the peak voltage signal and a first threshold voltage for outputting a comparison result; and a propagation delay circuit coupled to the comparing unit for receiving the comparison result and outputting an (pulse width modulation) PWM signal to turn on the switching device after a delay time.