Patent ID: 6320765
Filing Date: 2001-11-20
Classification: H02M,Y02B

Abstract:
A switching power circuit comprising:switching means having a main switching element for intermittently outputting a DC input voltage supplied thereto;a primary parallel resonance capacitor so provided as to constitute a primary parallel resonance circuit which turns the operation of said switching means into a voltage resonance type;an insulating converter transformer where a gap is formed in such a manner as to obtain a required coupling coefficient to acquire coarse coupling with regard to the primary and secondary sides, and the output of said switching means obtained on the primary side is transmitted to the secondary side;a secondary parallel resonance circuit formed by connecting a secondary parallel resonance capacitor in parallel to a secondary winding of said insulating converter transformer;DC output voltage generating means so formed as to generate a secondary DC output voltage by inputting and rectifying an alternating voltage obtained from the secondary winding of said insulating converter transformer;switching drive means for driving said main switching means to execute constant voltage control thereof by changing the on/off duty ratio in each switching period at a predetermined constant switching frequency in accordance with the level of the secondary DC output voltage; andactive clamp means having an auxiliary switching element to perform a switching operation in such a manner as to obtain predetermined on/off times changeable in accordance with the on/off times of said main switching element, thereby clamping the primary parallel resonance voltage generated across said primary parallel resonance capacitor during the off-time of said main switching element.