Patent ID: 8472214

Claim:
A control circuit for a flyback power converter including a transformer and a power switch connected to a primary side of the transformer, to switch the power switch so as for the transformer to convert an input voltage into an output voltage, the control circuit comprising: a sampling and holding circuit extracting a variation of a sensing signal during a preset time period, wherein the sensing signal is a function of the input voltage; a compensation circuit connected to the sampling and holding circuit, compensating a first feedback signal according to the variation of the sensing signal to generate a second feedback signal varying with the input voltage, wherein the first feedback signal is a function of the output voltage; a pulse width modulation circuit connected to the compensation circuit, determining an on-time of the power switch according to the sensing signal and the second feedback signal; and a minimum on-time modulation circuit connected to the sampling and holding circuit, modulating a minimum on-time of the power switch according to the variation of the sensing signal, whereby the minimum on-time of the power switch is modulated according to a variation of the input voltage.