Patent ID: 7242595
Filing Date: 2007-07-10
Classification: H02M,Y02B

Abstract:
1. A switching power supply circuit, comprising: a switching element that receives a direct-current (DC) voltage and performs a switching operation to convert the direct-current voltage to an alternating-voltage; a converter transformer having a primary winding on a primary side and a secondary winding on a secondary side, one end of the primary winding being supplied with the direct-current voltage via a choke coil, another end of the primary winding being connected to the switching element, the alternating voltage being input to the primary winding, and the secondary winding having an alternating voltage induced therein by the primary winding; a primary side parallel resonant capacitor connected in parallel with the switching element, the primary side parallel resonant capacitor forming a primary side parallel resonant circuit having a resonance frequency governed by an inductance of the choke coil, a leakage inductance occurring in the primary winding of the converter transformer, and a capacitance of the primary side parallel resonant capacitor; a primary side series resonant capacitor connected to a point of connection between the primary winding of the converter transformer and the choke coil, the primary side series resonant capacitor forming a first primary side series resonant circuit having a resonance frequency governed by the inductance of the choke coil and a capacitance of the primary side series resonant capacitor, and the primary side series resonant capacitor forming a second primary side series resonant circuit having a resonance frequency governed by the leakage inductance occurring in the primary winding of the converter transformer and the capacitance of the primary side series resonant capacitor; a series connection circuit of a clamping capacitor and an auxiliary switch element that conducts when the switching element is not conducting, the series connection circuit being connected in parallel with a series connection circuit of the choke coil and the primary winding of the converter transformer, and the series connection circuit clamping a peak of a resonant pulse waveform occurring in the primary side parallel resonant circuit when the switching element is not conducting; a secondary side rectifying and smoothing circuit having a secondary side rectifying element and a secondary side smoothing capacitor, the secondary side rectifying and smoothing circuit generating an output direct-current voltage by rectifying and smoothing the alternating voltage induced in the secondary winding; and switching element controlling means for controlling the switching element based on the output direct-current voltage.