Patent ID: 8125105

Claim:
A power supply device that receives supply of electric power from a first electric power supply source or from a second electric power supply source and generates a predetermined DC voltage, comprising: a bidirectional voltage converter unit that includes a first terminal and a second terminal and performs step-up converting or step-down converting between the first terminal and the second terminal; a first switching unit 9 that switches a connection between the first electric power supply source and the first terminal of the bidirectional voltage converter; a second switching unit 7 that switches a connection between the second electric power supply source and the first terminal of the bidirectional voltage converter; a third switching unit that switches a connection between the first electric power supply source and the second terminal of the bidirectional voltage converter; an output unit that outputs a DC voltage at the second terminal of the bidirectional voltage converter unit as the predetermined DC voltage; and a switching control unit that controls switching of the first switching unit, the second switching unit and the third switching unit, wherein: if a first DC voltage obtained from the first electric power supply source is equal to the predetermined DC voltage and a second DC voltage obtained from the second electric power supply source is lower than the predetermined DC voltage, the switching control unit opens the first switching unit, closes the second switching unit and closes the third switching unit so that the first DC voltage is outputted as the predetermined DC voltage and the second DC voltage is converted to the predetermined DC voltage by the bidirectional voltage converter unit performing the step-up converting; and if the first DC voltage and the second DC voltage are lower than the predetermined DC voltage, the switching control unit opens the first switching unit, closes the second switching unit and closes the third switching unit so that the electric power from the first electric power supply source is transmitted to the second electric power supply source via the bidirectional voltage converter unit and thereby the second electric power supply is charged, and, after the second electric power supply has been charged, the switching control unit opens the third switching unit so that the second DC voltage is converted to the predetermined DC voltage by the bidirectional voltage converter unit performing the step-up converting.