Patent ID: 8027177

Claim:
An isolated switching power supply apparatus arranged to transfer energy from a primary side to a secondary side in response to an on/off operation of a first switching circuit, comprising: a direct-current power supply input unit arranged to receive a direct-current input voltage; and a first transformer including a first primary winding, a first secondary winding, a second secondary winding, and a third secondary winding that are magnetically coupled to each other; wherein the first switching circuit includes a parallel circuit including a first switching element, a first capacitor, and a first diode; a series circuit including the first primary winding and the first switching circuit is connected in series with the direct-current power supply input unit; a first inductor defined by a leakage inductance of the second secondary winding is arranged in series with the second secondary winding nf 1 ; a second inductor defined by a leakage inductance of the third secondary winding is arranged in series with the third secondary winding and a second capacitor defining a low-pass filter together with the first inductor and the second inductor; the second secondary winding and the third secondary winding are wound to include the same number of turns and to have opposite magnetic polarities; the first secondary winding, the second secondary winding, and the third secondary winding are connected in series with the first capacitor to define a closed loop; and an output terminal of the low-pass filter is arranged to output an output voltage.