Patent ID: 6496389
Filing Date: 2002-12-17
Classification: H02M,Y02B,Y02P

Abstract:
A switching power circuit comprising:a rectifying circuit for generating a DC input voltage by rectifying and smoothing an input AC power signal; an insulating converter transformer having a primary winding connected to a tertiary winding and separated by a gap from a secondary winding; switching means for outputting, to the primary winding of said insulating converter transformer, the DC input voltage by operation of a switching element; a primary side parallel resonance circuit for actuating said switching means in a voltage resonance mode, said primary side parallel resonance circuit including the primary winding of said insulating converter transformer and a parallel resonance capacitor; a secondary side resonance circuit including the secondary winding of said insulating converter transformer and a secondary side resonance capacitor; the secondary winding generating a secondary side alternating voltage in response to the DC input voltage output to the primary winding of said insulating converter transformer by said switching means; DC output voltage generating means connected to said secondary side resonance circuit and rectifying the secondary side alternating voltage obtained from the secondary winding of said insulating converter transformer, thereby generating a secondary side DC output voltage; constant voltage control means for maintaining the secondary side DC output voltage at a constant voltage level by providing feedback to the switching element in accordance with the level of the secondary side DC output voltage; and power factor improving means for improving a power factor of said switching power circuit; said power factor improving means including the tertiary winding of the insulating converter transformer; a resonance capacitor for feeding back, to a rectified current path, the switched DC input voltage transferred from the primary winding to the tertiary winding; a fast recovery diode in the rectified current path to perform a switching operation in accordance with the switched DC input voltage fed back to the current path; and an inductor; the switched DC input voltage fed back via the tertiary winding resulting in an increased voltage across the fast recovery diode.