Patent ID: 7855899

Claim:
A control circuit of a power converter, comprising: a switching circuit, coupled to a feedback loop of the power converter to generate a switching signal in response to a feedback signal for output regulation, wherein the feedback loop is from a secondary winding of a transformer of the power converter, and the feedback signal is associated with an output voltage of the power converter; a soft start circuit, coupled to switching circuit and generating a soft start signal to control the switching signal; a resistive device, coupled to the feedback loop, wherein the resistive device comprises a transistor connected with a first resistor in parallel, the transistor directly connected to a voltage supply and a second resistor connected with the first resistor in series; and a comparison circuit, coupled to the feedback loop and directly connected to the switching circuit for comparing the feedback signal with a threshold signal and generating a mode signal to the switching circuit, wherein the mode signal is used to disable the switching signal for saving power, control on/off of the transistor of the resistive device so as to modulate an impedance of the resistive device and reset the soft start circuit for enabling soft start of the switching signal when the switching signal is enabled.