Switching power supply apparatus including a plurality of outputs

A switching power supply apparatus comprising:

• a first serial circuit connected to a power supply input portion to which a DC input voltage is input, and including a first switching element on a high side and a second switching element on a low side;
• a second serial circuit connected to the power supply input portion to which the DC input voltage is input, and including a third switching element on a high side and a fourth switching element on a low side;
• a transformer including at least a primary winding and a secondary winding which are magnetically coupled to each other;
• a serial resonance circuit including one end connected to a junction between the first switching element and the second switching element and the other end connected to a junction between the third switching element and the fourth switching element, the serial resonance circuit including the primary winding of the transformer, an inductor, and a capacitor;
• a first rectifying and smoothing circuit arranged to rectify and smooth a voltage generated in the secondary winding of the transformer during an on-period of the first switching element and the fourth switching element, and to take out a first output voltage;
• a second rectifying and smoothing circuit arranged to rectify and smooth a voltage generated in the secondary winding of the transformer during an on-period of the second switching element and the third switching element, and to take out a second output voltage;
• and
• a switching control circuit arranged and programmed to drive the first and fourth switching elements and the second and third switching elements to be repeatedly turned on/off in a complementary way, and arranged and programmed to control the on-time of the first and fourth switching elements and the on-time of the second and third switching elements in accordance with the first output voltage and the second output voltage, respectively, so as to control the first output voltage and the second output voltage;
• wherein
• the first rectifying and smoothing circuit includes a first rectifier switching element and a smoothing capacitor;
• the second rectifying and smoothing circuit includes a second rectifier switching element and a smoothing capacitor;
• and
• the switching control circuit includes a control circuit arranged and programmed to:
• turn on the first rectifier switching element in response to turning-on of the first switching element, and turn off the first rectifier switching element in response to turning-off of the first switching element;
• turn on the second rectifier switching element in response to turning-on of the second switching element, and turn off the second rectifier switching element in response to turning-off of the second switching element;
• and
• continuously hold one of the first and second rectifier switching elements in an on-state even after a current on a secondary side of the transformer has been reduced to be negative with a resonance and to cause the current to be regenerated from an output of the switching power supply apparatus.