Patent ID: 7816812

Claim:
An electronic device comprising: a first input terminal to which a first DC supply voltage of a fuel cell system having a controllable supply voltage is provided; a second input terminal to which a second DC supply voltage of a rechargeable battery is provided; a DC voltage conversion circuit for receiving the first and second DC supply voltages from the first and second input terminals, and supplying a current of a desired DC voltage to a load, wherein a power efficiency of voltage conversion of the DC voltage conversion circuit becomes higher as a difference between the received DC supply voltage and the desired DC voltage becomes lower; a charging circuit for receiving the first DC supply voltage from the first input terminal, and supplying a DC supply voltage for charging to the second input terminal; and a control circuit for receiving, from the rechargeable battery, a value of the second DC supply voltage of the rechargeable battery, and determining a desired value of the first DC supply voltage to be a sum of the received value of the second DC supply voltage of the rechargeable battery and a given value, and providing the determined desired value to the fuel cell system.