Adaptive active clamp of flyback power converter with high efficiency for heavy load and light load

A method for controlling a flyback power converter with an active-damper, comprising:

• generating a switching signal in accordance with a feedback signal for switching a low-side transistor and regulating an output of the flyback power converter;
• and
• generating an active-clamp signal in accordance with a demagnetizing time of a transformer;
• wherein the pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition;
• the low-side transistor is coupled to switch the transformer;
• the active-clamp signal is coupled to drive the active-damper, the active-damper is coupled in parallel with the transformer.

A control circuit of an active clamp flyback power converter, comprising:

• a low-side transistor coupled to switch a transformer;
• an active-damper coupled in parallel with the transformer;
• a high-side drive circuit coupled to drive the active-damper;
• and
• a controller generating a switching signal and an active-clamp signal;
• wherein the switching signal is coupled to drive the low-side transistor;
• the switching signal is generated in accordance with a feedback signal for regulating an output of the active clamp flyback power converter;
• the active-clamp signal is coupled to control the high-side drive circuit and the active-damper;
• the pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition.