Patent ID: 7894212

Claim:
A switching power supply device for use with a DC power supply, comprising: a first series circuit of a first switching element and a second switching element connected in parallel with the DC power supply; an isolation transformer having primary and secondary windings and first and second auxiliary windings, a wound layer including the primary windings being provided in a first layer between a second layer including the first auxiliary windings and second auxiliary windings, and a third layer including substantially all of the secondary windings; a capacitor connected in series with the isolation transformer primary windings to define a second series circuit, the second series circuit being connected in parallel with the second switching element; a rectifying and smoothing circuit, including a rectifying diode and a smoothing capacitor, connected to the secondary windings of the isolation transformer; a first control circuit configured to turn on and off the first switching element based on a voltage generated in the first auxiliary windings; and a second control circuit configured to turn on and off the second switching element respectively as the first control circuit turns off and on the first switching element, based on a voltage generated in the second auxiliary windings, whereby the first and second switching elements alternately turn on and off, the rectifying and smoothing circuit providing a DC output in response thereto, wherein the first auxiliary windings are disposed over a first portion of the primary windings and the second auxiliary windings are disposed over a second portion of the primary windings, so that the first and second auxiliary windings do not overlap one another, or the first auxiliary windings are disposed under a first portion of the primary windings and the second auxiliary windings are disposed under a second portion of the primary windings, so that the first and second auxiliary windings do not overlap one another.