Power supply device

A power supply device for supplying electric power from a power source to a load, the power supply device comprising:

• a first power line configured to connect the power source to the load via a relay,
• at least one diode disposed on the first power line between the relay and the load;
• a second power line disposed in parallel with the first power line and configured to connect the power source to the load via a switching element;
• and
• a controller configured to control on and off of the switching element,
• wherein
• a voltage drop that occurs across the switching element when the switching element is turned on is smaller than a voltage drop that occurs across the at least one diode when the relay is turned on, and
• the controller is configured to determine whether the switching element is on or off based on a voltage across the at least one diode and a voltage supplied to the load.