Switching power supply apparatus

A switching power supply apparatus which receives an AC voltage, the switching power supply apparatus comprising:

• a transformer including a primary winding and a secondary winding;
• a bidirectional switch connected in series with the primary winding;
• and
• a Snubber circuit connected in parallel with the primary winding,
• wherein the AC voltage is applied to a series circuit including (i) the primary winding and (ii) the bidirectional switch, and
• the Snubber circuit includes an element which is switchable between (i) a first diode characteristic in which conduction is established in a single direction and (ii) a second diode characteristic in which conduction is established in an opposite direction to the single direction.

A switching power supply apparatus which converts an input AC voltage into a DC voltage, the switching power supply apparatus comprising:

• an output terminal for outputting the DC voltage;
• a transformer including a primary winding and a secondary winding;
• a first bidirectional switch connected in series with the primary winding, the first bidirectional switch including a first gate and a second gate;
• and
• a full-wave rectifier circuit between (i) a first terminal and a second terminal of the secondary winding and (ii) the output terminal, the full-wave rectifier circuit including a first current path and a second current path each of which is switchable between conduction and non-conduction,
• wherein the AC voltage is applied to a series circuit including (i) the primary winding and (ii) the first bidirectional switch,
• the full-wave rectifier circuit performs full-wave rectification on a voltage applied to the primary winding, by performing selective switching such that conduction is established in one of the first current path and the second current path and no conduction is established in the other one of the first current path and the second current path, and
• a first control signal is applied to the first gate of the first bidirectional switch and a second control signal is applied to the second gate of the first bidirectional switch,
• both of a frequency of the first control signal and a frequency of the second control signal are switched in synchronization with switching between polarities of the AC voltage, and
• when the frequency of the first control signal is a first frequency, the frequency of the second control signal is a second frequency which is different from the first frequency.

A switching power supply apparatus which converts an input AC voltage to a DC voltage to supply the DC voltage to a load, the switching power supply apparatus comprising:

• a first output terminal and a second output terminal which are connected to each other with the load therebetween, and which are for outputting the DC voltage;
• a transformer including a primary winding and a secondary winding;
• and
• a first bidirectional switch connected in series with the primary winding,
• wherein the AC voltage is applied to a series circuit including (i) the primary winding and (ii) the first bidirectional switch,
• the secondary winding includes a first terminal, a second terminal, and a third terminal,
• the switching power supply apparatus further comprises:
• a second bidirectional switch between the first terminal and the first output terminal;
• and
• a third bidirectional switch between the second terminal and the second output terminal, and
• the third terminal is electrically connected to the second output terminal.