Patent ID: 9391528
Filing Date: 2016-07-12
CPC Classification: H02M

Claim Text:
1. An active clamp circuit for a flyback power converter, comprising: a power transistor coupled in series with a capacitor to develop an active-clamper, wherein the active-clamper is coupled in parallel with a primary winding of a transformer of the flyback power converter; a high-side transistor driver coupled to drive the power transistor; a charge-pump circuit coupled to a voltage source and the high-side transistor driver to provide a power supply to the high-side transistor driver; and a controller generating a control signal coupled to control the high-side transistor driver; wherein the control signal is generated in response to a demagnetizing time of the transformer, wherein the demagnetizing time is obtained according to a reflected signal and a threshold, and the reflected signal is generated from an auxiliary winding of the transformer; and wherein a pulse width of the control signal is a percentage of the demagnetizing time of the transformer, and the percentage of the demagnetizing time is determined by an attenuation rate of a voltage divider.