Flyback power converter and secondary-side control method thereof

A flyback power converter with secondary-side control, comprising:

• a primary-side controller, comprising:
• a first gate control signal generation circuit for generating a first gate control signal;
• a trigger pulse detection circuit for receiving a first voltage;
• and
• a start-up circuit coupled to the trigger pulse detection circuit and the first gate control signal generation circuit, wherein after the primary-side controller enters a start-up mode, the start-up circuit generates a first control signal to the first gate control signal generation circuit at a first predetermined valley of the first voltage, and the first gate control signal generation circuit generates the first gate control signal to turn on a power switch according to the first control signal;
• and
• a secondary-side controller, comprising:
• a voltage detection signal generation circuit coupled to an output terminal of a second side of the flyback power converter;
• a valley detection circuit for receiving a second voltage;
• and
• a second gate control signal generation circuit coupled to the voltage detection signal generation circuit and the valley detection circuit, wherein after the valley detection circuit detects a first coupling voltage corresponding to the first gate control signal on the second voltage, the second gate control signal generation circuit generates a trigger pulse to a synchronous switch at a second predetermined valley of the second voltage to make the primary-side controller enter a secondary-side control mode from the start-up mode.