Patent ID: 6370043
Filing Date: 2002-04-09
Classification: H02M

Abstract:
A switching power supply circuit, comprising:rectifier smoothing means for receiving an ac power supply, producing a rectified smoothed voltage having a level equal to that of the ac power supply and outputting the rectified smoothed voltage as a dc input voltage; an insulating converter transformer for transmitting a primary side output to a secondary side, said insulating converter transformer having a gap formed therein so that a coupling efficient (k) for a loose coupling is obtained; switching means including a switching element for switching the dc input voltage on and off so as to be outputted to a primary winding of said insulating converter transformer; a primary side resonance circuit formed from a leakage inductance component from said primary winding of said insulating converter transformer and a capacitance of a resonance capacitor to enable said switching means to operate as a voltage resonance type; a secondary side parallel resonance circuit including a secondary winding of said insulating converter transformer and a secondary side parallel resonance capacitor connected such that a parallel resonance circuit is formed from a leakage inductance component of said secondary winding of said insulating converter transformer and a capacitance of said secondary side parallel resonance capacitor; dc output voltage production means for receiving an alternating voltage obtained at said secondary winding of said insulating converter transformer and performing a half-wave rectification operation by an additive mode for the alternating voltage to produce a secondary side dc output voltage; and constant voltage control means for varying a switching frequency of said switching element in response to a level of the secondary side dc output voltage to perform constant voltage control of the secondary side output voltage.