Active clamp flyback converter and control method

A control method for an active clamp flyback converter, wherein the active clamp flyback converter comprises:

• a transformer, comprising a primary side winding and a secondary side winding coupled with each other;
• a primary side switch, connected in series to the primary side winding;
• a clamp branch circuit, connected in parallel to the primary side winding or in parallel to the primary side switch;
• wherein the clamp branch circuit comprises a clamp switch and a clamp capacitor connected in series;
• wherein the control method comprises:
• in response to that an input voltage of the active clamp flyback converter is less than a preset voltage threshold, or the input voltage of the active clamp flyback converter is less than a product of an output voltage of the active clamp flyback converter and a turns ratio of the transformer, performing following steps:
• in a same switching cycle, controlling the clamp switch to turn on when the transformer is in a demagnetization stage;
• and controlling the clamp switch to turn off when a resonant current of the clamp capacitor and a leakage inductance of the transformer reaches a preset current threshold.