Resonant switching power supply circuit with voltage doubler output

A switching power supply circuit, comprising:

• rectifier smoothing means for receiving a commercial ac power supply, producing a rectified smoothed voltage and outputting said rectified smoothed voltage as a dc 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 which is efficient for a loose coupling is obtained;
• switching means including a switching element for switching the dc input voltage between on and off states so as to be outputted to a primary winding of said insulating converter transformer;
• a primary side parallel resonance circuit formed from a leakage inductance component from said primary winding of said insulating converter transformer and a capacitance of a parallel resonance capacitor for enabling said switching means to operate as a voltage resonance type;
• a secondary side series resonance circuit including a secondary side series resonance capacitor and a secondary winding of said insulating converter transformer, said capacitor connected in series to said secondary winding of said insulating converter transformer, such that a series 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 series 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 voltage multiplying full-wave rectification operation for the alternating voltage to produce a secondary side dc output voltage substantially equal to twice the input voltage level;
• 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.