A control circuit of a power converter is coupled to an output stage and controls it to convert an input voltage into an output voltage and generate an output current. The control circuit includes a ripple generation circuit, a synthesis circuit, an error amplifier, a comparator and a PWM circuit. The ripple generation circuit generates a ripple signal according to an input voltage, an output voltage and output current. The synthesis circuit receives the ripple signal and a first feedback signal related to output voltage to provide a second feedback signal. The error amplifier receives the second feedback signal and a reference voltage to generate an error signal. The comparator receives a ramp signal and error signal to generate a comparison signal. The PWM circuit generates a PWM signal to control output stage according to the comparison signal. A slope of ripple signal is changed with the output current.