Switching power supply with pulse frequency modulation control

A switching power supply comprising:

• a DC power supply;
• a first series circuit connected in parallel to the DC power supply, the first series circuit comprising a first switching circuit and a second switching circuit connected in series to each other, the first switching circuit comprising a first parallel circuit having a first switching device, a first diode and a first capacitor, the second switching circuit comprising a second parallel circuit having a second switching device, a second diode and a second capacitor;
• and
• a second series circuit comprising an inductance element, a primary winding of a first transformer, a primary winding of a second transformer, and a capacitor, the second series circuit being connected in parallel to any of the first and second switching circuits;
• the switching power supply rectifying and smoothing a voltage generated across a secondary winding of the first transformer and a voltage generated across a secondary winding of the second transformer for obtaining a DC output;
• wherein the switching power supply turns on and off the first switching device and the second switching device alternately at a switching frequency higher than a series resonance frequency determined by a sum of an inductance value of the inductance element, an inductance value of the first transformer and an inductance value of the second transformer, and a static capacitance value of the capacitor.