Patent ID: 7113411

Claim:
A switching power supply apparatus comprising: a first switch circuit S 1 including a parallel connection circuit having a first switch device Q 1 , a first diode D 1 , and a first capacitor Cds 1 ; a second switch circuit S 2 including a parallel connection circuit having a second switch device Q 2 , a second diode D 2 , and a second capacitor Cds 2 ; an input-side rectifying circuit Da including at least one rectifying device for rectifying an AC input voltage; a third capacitor Ca to which the voltage rectified by the rectifying circuit Da is applied; a transformer T having a primary winding Lp and a secondary winding Ls; a rectifying and smoothing circuit RS connected to the secondary winding Ls; a first inductor Lr connected in series with the primary winding Lp; a second inductor Li connected so that a voltage of the third capacitor Ca is applied during an on-period for which the first switch circuit S 1 conducts; a third diode Di preventing a reverse current from flowing in the second inductor Li; a fourth capacitor Ci that is charged by excitation energy stored in the second inductor Li and that is connected so as to apply a voltage to the primary winding Lp during the on-period; a fifth capacitor Cr defining a closed loop together with the first inductor Lr, the primary winding Lp, and the second switch circuit S 2 ; and switching control circuits SC 1 and SC 2 arranged to alternately turn on and off the first and second switch devices with a period of time during which both switch devices are turned off therebetween.