CONTROL CIRCUITS AND METHODS FOR ACTIVE-CLAMP FLYBACK POWER CONVERTERS

摘要

A method for controlling an active-clamp flyback power converter is provided. The control method comprises: generating a first switch signal according to an output voltage and a current sensing signal, and selectively generating a second switch signal in a complementary or non-complementary control mode according to the current sensing signal and the first switch signal. The first switch signal is coupled to drive a low-side power switch for switching a transformer and the output voltage regulation of the active-clamp flyback power converter. The second switch signal is coupled to drive a high-side power switch for recycling leakage energy of the transformer and achieving a soft-switching of the low-side power switch. With the control method, the high-side power switch can adaptively switch in a complementary or non-complementary control mode depending on the output load and input voltage conditions.

主权项

1. An active-clamp flyback power converter comprising:
a first switch device comprising a first switch and a parallel-connected first diode, coupled to a primary winding of a transformer and switched according to a first switch signal to switch the transformer for regulating an output voltage of the active-clamp flyback power converter; a second switch device comprising a second switch and a parallel-connected second diode, and switched according to a second switch signal for recycling leakage energy of the transformer and achieving a soft-switching of the first switch; a clamp capacitor connected in series with the second switch device to develop an active-clamp circuit, wherein the active-clamp circuit is coupled in parallel with the primary winding of the transformer; and a control circuit generating the first switch signal according to the output voltage and a current sensing signal, and selectively generating the second switch signal in a complementary control mode or a non-complementary control mode according to the current sensing signal and the first switch signal,