CONTROL CIRCUIT FOR ACTIVE-CLAMP FLYBACK POWER CONVERTER WITH PROGRAMMABLE SWITCHING PERIOD

摘要

A method for controlling an active-clamp flyback power converter is provided. The method includes comprises: generating a switching signal in response to a feedback signal for switching a low-side transistor and regulating an output of the active-clamp flyback power converter; generating an active-clamp signal after the switching signal is disabled; generating a hysteresis bias to adjust the feedback signal; and generating a pulse signal periodically to enable the switching signal. The low-side transistor is coupled to switch a transformer. The switching signal is coupled to drive the low-side transistor. The active-clamp signal is coupled to drive a high-side transistor. A pulse width of the active-clamp signal is determined by a first resistor. The high-side transistor is connected in series with a capacitor to develop an active-clamp circuit. A minimum frequency of the switching signal is determined by a second resistor during a heavy load condition.

主权项

1. A control circuit of an active-clamp flyback power converter comprising:
a low-side transistor coupled to switch a transformer; a high-side transistor connected in series with a capacitor to develop an active-clamp circuit, wherein said active-clamp circuit is coupled in parallel with said transformer; a high-side driving circuit coupled to drive said high-side transistor; and a controller generating a switching signal and an active-clamp signal, wherein said switching signal is coupled to drive said low-side transistor, and said switching signal is generated in response to a feedback signal for regulating an output of said active-clamp flyback power converter, and wherein said active-clamp signal is coupled to said high-side driving circuit for controlling said high-side transistor, and a pulse width of said active-clamp signal is determined by a first resistor.