Patent ID: 8432058

Claim:
A power supply device comprising: a load including a smoothing capacitor used for precharging; a direct current power supply which supplies direct current power to the load and which includes a first electrode and a second electrode; a main contactor arranged between the load and the first electrode of the direct current power supply; a precharge contactor connected in parallel to the main contactor and including a first terminal electrically connected to the first electrode of the direct current power supply and a second terminal electrically connected to the load; a precharge resistor connected in parallel to the main contactor and in series to the precharge contactor between the first electrode of the direct current power source and the first terminal of the precharge contactor, wherein the smoothing capacitor undergoes precharging via the precharge resistor when the precharge contactor closes, and after completion of precharging, the main contactor is closed and the precharge contactor is open to start supplying the load with the direct current power; a voltage detection unit connected to a connection node, which is between the first terminal of the precharge contactor and the precharge resistor, and the second electrode of the direct current power supply, wherein the voltage detection unit obtains a first voltage detection value by detecting voltage between the connection node and the second electrode of the direct current power supply while the precharge contactor is open, wherein the first voltage detection value is a precharging saturation voltage corresponding to a power supply voltage supplied from the direct current power supply immediately before precharging is performed, and the voltage detection unit obtains a second voltage detection value by detecting voltage between the connection node and the second electrode of the direct current power supply while the precharge contactor is closed, wherein the second voltage detection value is a precharge voltage applied to the smoothing capacitor during precharging; and a determination unit which determines that precharging has been completed when the second voltage detection value becomes greater than a determination value set in accordance with the first voltage detection value.