Patent ID: 6356465
Filing Date: 2002-03-12
Classification: H02M,Y02B

Abstract:
A switching power supply circuit comprising:switching means including a main switching device for interrupting an inputted direct-current input voltage for output; a primary-side parallel resonant capacitor for forming a primary-side parallel resonant circuit that converts operation of said switching means into voltage resonance type operation; an isolating converter transformer for transmitting an output of said switching means obtained in a primary winding of the isolating converter transformer to a secondary winding thereof, the isolating converter transformer being formed so as to have loose coupling at a required coupling coefficient between the primary winding and the secondary winding; a secondary-side resonant circuit formed by connecting a secondary-side resonant capacitor to the secondary winding of said isolating converter transformer; a direct-current output voltage generating means for rectifying an alternating voltage inputted from the secondary winding of said isolating converter transformer and thereby providing a secondary-side direct-current output voltage; switching driving means for effecting control for constant voltage by driving said switching means for switching operation such that switching frequency of said switching means is variably controlled according to level of said secondary-side direct-current output voltage, and at the same time an on period of said switching means within one switching cycle is variably controlled while an off period thereof is fixed; and active clamp means for clamping a primary-side parallel resonance voltage generated across said primary-side parallel resonant capacitor, the active clamp means including an auxiliary switching device that is driven for switching operation such that the auxiliary switching device and said switching means perform on/off operation substantially alternately.