Patent ID: 6349046
Filing Date: 2002-02-19
Classification: H02M,Y02B

Abstract:
A switching power supply circuit comprising:an insulating converter transformer including a primary winding and a secondary winding insulated from each other, said primary winding and said secondary winding being loosely coupled to each other; a switching circuit including a switching device for performing switching operation on a current flowing into the primary winding of said insulating converter transformer at a fixed frequency; a primary-side parallel resonant capacitor provided on a primary side of said insulating converter transformer for forming a primary-side parallel resonant circuit in conjunction with inductance of said converter transformer; a secondary-side resonant capacitor provided on a secondary side of said insulating converter transformer for forming a secondary-side resonant circuit in conjunction with inductance of said converter transformer; a rectifier circuit for rectifying an alternating voltage obtained on the secondary side of said insulating converter transformer; an active clamp circuit provided on the secondary side of said insulating converter transformer for clamping the alternating voltage obtained on the secondary side of said insulating converter transformer in synchronism with the switching operation of said switching circuit; and a constant-voltage control circuit for effecting control for constant voltage by controlling a clamping period of said active clamp circuit and controlling an on/off-period duty ratio of a rectifying device of said rectifier circuit according to a level of output voltage of said rectifier circuit.