Patent ID: 6923279

Claim:
A power supply apparatus for a vehicle, comprising: a first battery unit; a second battery unit for a lower voltage than said first battery unit; an inverter circuit which inputs a voltage from said first battery unit through switches; a smoothing condenser provided between said first battery unit and said inverter circuit in parallel; a DC-DC converter provided between said smoothing condenser and said second battery unit to voltage-convert electric energy stored in said first battery unit or said smoothing condenser to supply to said second battery unit, and to voltage-convert electric energy stored in said second battery unit to supply to said smoothing condenser; an electronic control unit which controls said DC-DC converter before starting power supply to said inverter circuit, such that said switches are closed after said smoothing condenser is charged to a voltage within a predetermined permission voltage range from the voltage of said first battery unit; wherein said DC-DC converter comprises: a voltage decreasing switching circuit connected with said smoothing condenser; a voltage increasing switching circuit connected with said second battery unit; and a transformer provided between said voltage decreasing switching circuit and said voltage increasing switching circuit, and said voltage increasing switching circuit is driven by said electronic control unit to carry out a switching operation such that the voltage from said second battery unit is boosted and supplied to said smoothing condenser, and said voltage decreasing switching circuit is driven by said electronic control unit to carry out a switching operation such that the voltage supplied through said switches from said first battery unit is decreased and supplied to said second battery unit; wherein said electronic control unit stops the switching operation of said voltage increasing switching circuit, when the voltage applied to said smoothing condenser is higher than an output voltage of said first battery unit, and operates said voltage decreasing switching circuit.