Constant on-time flyback converter and control method thereof

A constant on-time flyback converter comprises:

• a main switch;
• an isolator;
• a transformer comprising a primary coil at a primary side connected in series with the main switch between an input terminal of the constant on-time flyback converter and a ground;
• and
• a secondary coil on a secondary side of the transformer connected between an output terminal of the constant on-time flyback converter and a reference ground potential of the secondary side;
• a primary controller on the primary side connected to a gate of the main switch;
• and
• a secondary controller on the secondary side coupled to the primary controller on the primary side through the isolator, the secondary controller generating a first control signal according to an output from the output terminal of the constant on-time flyback converter;
• wherein the primary controller comprises:
• a receiving unit connected to the isolator to receive the first control signal generated by the secondary controller;
• wherein the receiving unit outputs the first control signal as a trigger-on signal;
• a driving unit receives the first control signal and to output a gate-on control signal to turn on the main switch;
• and
• a first control unit receives the gate-on control signal and generates a second control signal as a trigger-off signal after a constant on-time;
• wherein the driving unit receives the second control signal to output a gate-off control signal to turn off the main switch.