Ripple suppression circuit and a ripple suppression method for quasi-resonant flyback power supply

A ripple suppression circuit for quasi-resonant flyback power supply, the ripple suppression circuit comprising:

• a compensation circuit configured to generate a compensation signal, wherein the compensation signal is generated based on bus voltage;
• and
• a control circuit configured to compare a first signal with a second signal to provide a control signal, wherein the control signal is configured to control a power switch of the quasi-resonant flyback power supply turning from an on state to an off state, and the first signal is compensated by the compensation signal;
• wherein the ripple suppression circuit further comprises a reference circuit, the reference circuit configured to generate a reference signal, the reference signal generated based on an output voltage of the quasi-resonant flyback power supply;
• wherein the first signal represents sum of the reference signal and the compensation signal, and the second signal represents primary side current of a transformer of the quasi-resonant flyback power supply;
• wherein the control circuit comprises:
• an addition circuit having a first input terminal, a second input terminal and an output terminal, the first input terminal of the addition circuit coupled to the compensation circuit, the second input terminal of the addition circuit coupled to the reference circuit, the addition circuit configured to add the compensation signal and the reference signal to generate the first signal;
• and
• a comparison circuit having a first input terminal and a second input terminal, the first input terminal of the comparison circuit coupled to the second signal, the second input terminal of the comparison circuit coupled to the output terminal of the addition circuit;
• when the second signal is greater than the first signal, the control circuit controls the power switch of the quasi-resonant flyback power supply turning from the on state to the off state;
• and
• wherein a relation between the compensation signal and the bus voltage is:
• CS_comp=K0+K1/Vbus;
• wherein CS_comp is the compensation signal, K0 is a constant, K1 is a non-zero constant, and Vbus is the bus voltage.