Patent ID: 6317337
Filing Date: 2001-11-13
Classification: H02M,Y02B

Abstract:
A switching power supply circuit comprising:rectifying and smoothing means for being supplied with a commercial AC power supply, generating a rectified and smoothed voltage having a level nearly equal to the level of the commercial AC power supply, and outputting the generated rectified and smoothed voltage as a DC input voltage;an insulated converter transformer having magnetical cores with a gap to provide a loose magnetical coupling coefficient, for transmitting a primary-side power to a secondary side;switching means for turning on and off periodically said DC input voltage with a switching element and outputting a pulsating voltage to a primary winding of said insulated converter transformer;a primary-side parallel resonant circuit comprising at least an inductance including a leakage inductance of the primary winding of said insulated converter transformer and a capacitance of a parallel resonant capacitor, for causing said switching means to operate in a voltage-resonant manner;a secondary-side parallel resonant circuit including a secondary-side parallel resonant capacitor connected parallel to a secondary winding of said insulated converter transformer, said secondary-side parallel resonant circuit comprising an inductance of the secondary winding including a leakage inductance of said insulated converter transformer and the capacitance of said secondary-side parallel resonant capacitor;DC output voltage generating means for being supplied with an alternating voltage induced across the secondary winding of said insulated converter transformer, and rectifying the alternating voltage by way of full-wave rectification to generate a secondary-side DC output voltage; andvoltage regulating means for varying a switching frequency of said switching element depending on the level of said secondary-side DC output voltage to effect composite control on a resonant impedance of said primary-side parallel resonant circuit and a conduction angle of said switching element thereby to perform constant-voltage control over a secondary-side output voltage.