Isolated switching power supply apparatus

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 nf1;
• 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.