Abstract: The present invention provides a flyback power converter and a control circuit thereof. The flyback power converter includes a transformer, a power switch, a driver, a synchronous rectification (SR) switch, a controller, and a signal coupler circuit. The transformer has a primary winding and a secondary winding. The power switch controls the conduction time of the primary winding; and the SR switch controls the conduction time of the secondary winding. The controller controls the SR switch and generates an ON pulse signal and an OFF pulse signal in a normal operation mode. When an output voltage reaches a lower limit voltage, the flyback power converter operates in the normal operation mode. The driver generates a switching signal according to the ON pulse signal and the OFF pulse signal in the normal operation mode, to determine a start conduction time point and an end conduction time point of the primary winding.

Abstract: The present invention provides a flyback power converter and a control circuit and a control method thereof. The flyback power converter includes: a power stage circuit, a voltage sense circuit, a current sense circuit, and a control circuit. When the flyback power converter operates in a quasi-resonant mode, the control circuit determines a time point of turning OFF a power switch in the power stage circuit according to a current sense signal, a pulse width modulation (PWM) frequency of a PWM signal, and a predetermined threshold, wherein the control circuit adaptively adjusts an ON period of the power switch, or adaptively adjusts an operation bandwidth or an amplifier gain of an error amplifier circuit in a feedback control loop according to the PWM frequency to mitigate an output voltage ripple.