Relay-welding detection circuit and power supplying system

A power supply system for an electric vehicle that supplies/cuts off a current to an electric storage apparatus for supplying power to a vehicle driving motor in a charging path from an external power supply to the electric storage apparatus, the system comprising:

• a relay welding detection circuit that includes a power supply-side relay and a ground-side relay whose on or off state is independently controllable and that detects the welding of the relays;
• a power supply section that is capable of supplying welding detection power independently from the external power supply;
• a voltage detection circuit to which almost no current flows from a side of the power supply-side relay close to the external power supply and which controls whether to supply the welding detection power to the power supply section on the basis of a voltage on the external power supply side of the power supply-side relay;
• and
• a control section that independently controls the on or off state of the power supply-side relay and the ground-side relay, that detects the welding of the relays on the basis of whether the voltage detection circuit has supplied the welding detection power, and that is electrically insulated from the voltage detection circuit,
• wherein the voltage detection circuit is a switch using a transistor,
• a collector terminal of the transistor is electrically connected to a positive terminal of the power supply section,
• an emitter terminal of the transistor is electrically connected to a charging path on the external power supply side of the ground-side relay,
• a base terminal of the transistor is electrically connected to a charging path on the external power supply side of the power supply-side relay, and
• a negative terminal of the power supply section is connected to a negative terminal of the electric storage apparatus.