Active clamp circuits for flyback power converters

摘要

An active clamp circuit for a flyback power converter is provided. The active clamp circuit includes a power transistor, a capacitor, a high-side transistor driver, a charge-pump circuit, and a controller. The power transistor is coupled in series with a capacitor to develop an active-clamper. The active-damper is coupled in parallel with a primary winding of a transformer of the flyback power converter. The high-side transistor driver is coupled to drive the power transistor. The charge-pump circuit is coupled to a voltage source and the high-side transistor driver to provide a power supply to the high-side transistor driver. The controller generates a control signal coupled to control the high-side transistor driver. The control signal is generated in response to a demagnetizing time of the transformer.

主权项

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.