A control circuit of a power converter includes: an error detection circuit, configured to operably generate an error signal according to a reference signal and a feedback signal when coupling with an external feedback node of an external feedback circuit; an output signal detecting circuit, positioned inside the control circuit, configured to operably receive and detect an output signal of the power converter to generate a representative signal; an on time deciding circuit, coupled with the output signal detecting circuit, configured to operably generate an on time signal according to the representative signal; and a control signal generating circuit, coupled with the error detection circuit and the on time deciding circuit, configured to operably control on time of one or more power switches of the power converter according to the error signal and the on time signal.