Active clamp flyback converter having clamp switch and clamp capacitor and control ic for controlling the clamp switch to limit resonance current

Abstract

An active clamp flyback converter includes a main switch, a primary winding that is electrically connected in series with the main switch, a clamp switch that is electrically connected to a connection point between the main switch and the primary winding, a clamp capacitor that is connected in series with the clamp switch, and a controller that outputs a first ON signal to control the main switch and a second ON signal to control the clamp switch during a period when the main switch is off. The controller outputs the second ON signal during a half cycle or more of a resonance period, in which the resonance current flowing in a resonance circuit comprising the clamp capacitor and a leakage inductance generated when the clam switch is turned on is limited by an excitation current of an excitation inductance of the primary winding.