Patent ID: 6366476
Filing Date: 2002-04-02
Classification: H02M,Y02B

Abstract:
A switching power supply circuit comprising:switching means showing a main switching device for interrupting an inputted direct-current input voltage; a primary-side parallel resonant capacitor for forming a primary-side parallel resonant circuit that converts operation of said switching means into a voltage resonance type operation; an isolating converter transformer having a primary-side winding and a secondary-side winding for transmitting an output of said switching means obtained in said primary-side winding to said secondary-side winding, said primary-side winding and said secondary-side winding being wound so as to be loosely coupled to each other with a predetermined coupling coefficient; a secondary-side resonant circuit formed by connecting a secondary-side resonant capacitor to said secondary-side winding; direct-current output voltage generating means for rectifying an alternating voltage inputted from said secondary-side winding and thereby providing a direct-current output voltage; active clamp means for clamping a primary-side parallel resonance voltage generated across said primary-side parallel resonant capacitor during an off period of said main switching device, said active clamp means including an auxiliary switching device driven for switching operation by self-oscillation driving; and switching driving means for effecting control for constant voltage by driving said main switching device for said switching operation such that a switching frequency of said main switching device is variably controlled according to level of said direct-current output voltage, and concurrently, an on/off period of said main switching device within one switching cycle is changed.