Patent ID: 7414864

Claim:
A switching power supply apparatus comprising: a first switching circuit including a first switching element, a first diode, and a first capacitor; a first transformer including a primary winding and a secondary winding; a first inductor serially-connected to the primary winding; a rectifying and smoothing circuit connected to the secondary winding; a rectifying circuit located on an input side of the switching power supply apparatus and including at least one rectifying element arranged to rectify an AC voltage; a second inductor connected so that a rectifying voltage obtained by the rectifying circuit is applied for an on-period so as to set the first switching circuit to a conductive state; a second switching circuit including a parallel connecting circuit including a second switching element, a second diode, and a second capacitor; a third capacitor connected so that excitation energy in the second inductor is charged and a voltage is applied to the primary winding of the first transformer for the on-period; a switching control circuit arranged to control the first switching element so as to obtain an output from the rectifying and smoothing circuit connected to the secondary winding; and a fourth capacitor serially-connected to the second switching circuit to define a serial circuit; wherein one end of the serial circuit of the second switching circuit and the fourth capacitor is connected to one end of the first switching circuit; said switching control circuit controls the operation so that the first switching element is turned off and then the second switching element is turned on, and the second switching element is turned off and then the first switching element is turned on, thereby controlling the amount of charging of the third capacitor via the first switching circuit for the on-period; and the excitation energy in the second inductor is charged to the third capacitor when the first switching element is turned off.