Patent ID: 7209369
Filing Date: 2007-04-24
Classification: H02M,Y02B

Abstract:
1. A switching power supply circuit comprising: a switching element that implements switching for a direct-current (DC) voltage to convert the DC voltage into an alternating-current (AC) voltage; a converter transformer that includes a primary winding and a secondary winding, the AC voltage arising from conversion by the switching element being input to the primary winding so that an AC voltage is generated in the secondary winding; a secondary-side rectifying and smoothing circuit that includes a secondary-side rectifier element and a secondary-side smoothing capacitor for rectifying and smoothing the AC voltage generated in the secondary winding to produce an output DC voltage; a switching element control unit that controls the switching element based on the output DC voltage; a choke coil that is supplied with the DC voltage through one end, and is connected via the other end to one winding end of the primary winding in the converter transformer and one terminal of the switching element; a primary-side series resonant circuit that is formed by connecting a primary-side series resonant capacitor between the other winding end of the primary winding in the converter transformer and the other terminal of the switching element, and has a resonant frequency dominated by a leakage inductance arising in the primary winding in the converter transformer and the primary-side series resonant capacitor; a primary-side parallel resonant circuit that is formed by connecting a primary-side parallel resonant capacitor in parallel to the switching element, and has a resonant frequency dominated by the leakage inductance arising in the primary winding and the primary-side parallel resonant capacitor; and a series circuit that is formed of a clamp capacitor and an auxiliary switch element, and is connected in parallel to the choke coil, wherein the auxiliary switch element is controlled so as to conduct in a non-conducting period of the switching element.