Power supply device

1. A power supply device comprising:

a transformer including a primary winding and a first secondary winding;

a first switching element on a secondary side of the transformer, the first switching element being configured to perform synchronous rectification;

a first rectifier on the secondary side of the transformer, the first rectifier being connected in series to the first switching element, one end of the first secondary winding being connected between the first switching element and the first rectifier;

a first capacitor and a second capacitor on the secondary side of the transformer, the first capacitor and the second capacitor being connected directly in series, the first capacitor including first and second electrodes, the second capacitor including third and fourth electrodes, the first electrode being connected directly to the first switching element and a ground, the second electrode being connected to the third electrode, and the fourth electrode being connected to the first rectifier; and

a coil on the secondary side of the transformer, one end of the coil being connected to an other end of the first secondary winding, an other end of the coil being connected between the second electrode of the first capacitor and the third electrode of the second capacitor and being connected to a battery via an output terminal, on the secondary side, of the power supply device,

wherein the first capacitor and the second capacitor are configured to charge by voltage-dividing, via the first rectifier, a first surge voltage to be generated in the first switching element by energy supplied from the battery and charged in the coil in a first case that the battery becomes larger in voltage than the output terminal, and the first switching element is turned off.

2. The power supply device according to claim 1 ,

further comprising

a second switching element on the secondary side of the transformer, the second switching element being configured to perform synchronous rectification;

a second rectifier on the secondary side of the transformer, the second rectifier being connected in series to the second switching element, wherein

the transformer further includes a second secondary winding,

one end of the second secondary winding being connected to the other end of the first secondary winding, an other end of the second secondary winding being connected between the second switching element and the second rectifier,

the first electrode of the first capacitor is connected directly to the first switching element, the second switching element, and the ground,

the fourth electrode of the second capacitor is connected directly to the first rectifier and the second rectifier, and

the first capacitor and the second capacitor are configured to charge by voltage-dividing, via the first rectifier and the second rectifier, a second surge voltage to be generated in the first switching element and the second switching element by energy supplied from the battery and charged in the coil in a second case that the battery becomes larger in voltage than the output terminal, and the first switching element and the second switching element are turned off.

3. A power supply device comprising:

a transformer including a primary winding, a first secondary winding, and a second secondary winding;

a first series circuit on a secondary side of the transformer, the first series circuit including a first switching element configured to perform synchronous rectification and a first rectifier connected in series to the first switching element, wherein one end of the first secondary winding is connected between the first switching element and the first rectifier;

a second series circuit on the secondary side of the transformer, the second series circuit including a second switching element configured to perform synchronous rectification and a second rectifier connected in series to the second switching element, the second series circuit being connected in parallel to the first series circuit, wherein one end of the second secondary winding is connected between the second switching element and the second rectifier;

a third series circuit on the secondary side of the transformer, the third series circuit including a first capacitor and a second capacitor connected directly in series, the third series circuit being connected in parallel to the first series circuit and the second series circuit, the first capacitor including first and second electrodes, the second capacitor including third and fourth electrodes, the first electrode being connected directly to the first switching element, the second switching element, and a ground, the second electrode being connected to the third electrode, and the fourth electrode being connected to the first rectifier and the second rectifier;

a coil on the secondary side of the transformer, one end of the coil being connected to a connection point between the first secondary winding and the second secondary winding, and another end of the coil being connected between the second electrode of the first capacitor and third electrode of the second capacitor and being connected to a battery via an output terminal, on the secondary side, of the power supply device; and

a control circuit on the secondary side of the transformer, the control circuit being connected to the first switching element and the second switching element, and the control circuit being configured to control on and off of the first switching element and the second switching element,

wherein the first capacitor and the second capacitor are configured to charge by voltage-dividing, via the first rectifier and the second rectifier, a surge voltage to be generated in the first switching element and the second switching element by energy supplied from the battery and charged in the coil in a case that the battery becomes larger in voltage than the output terminal, and the first switching element and the second switching element are turned off.

4. The power supply device according to claim 3 , wherein a capacitance of the second capacitor is set in accordance with a capacitance ratio of the first switching element and the second switching element, and

the capacitance ratio is set larger than a maximum voltage value of the surge voltage.

5. The power source device according to claim 3 , wherein the capacitance of the second capacitor is set smaller than a capacitance of the first capacitor.