Patent ID: 7667350

Claim:
A method of controlling an electric power source for supplying electric power to a charging terminal of an electronic device on which a secondary battery is mounted, wherein the electric power source is an external battery charger for the secondary battery of the electronic device and comprises a fuel cell and an auxiliary power source connected to the fuel cell in parallel and an output terminal of the electric power source can be connected to the charging terminal of the electronic device, the method comprising: supplying the electric power to the charging terminal of the electronic device from the fuel cell and the auxiliary electric power source to charge the secondary battery by turning on the output terminal side of the electric power source at the time when a voltage of the auxiliary power source reaches an upper-limit threshold of a charging voltage of the auxiliary power source, interrupting the supply of the electric power to the charging terminal of the electronic device and charging instead the auxiliary electric power source from the fuel cell by turning off the output terminal side of the electric power source at the time when the voltage of the auxiliary power source reaches a lower-limit threshold of a discharge voltage of the auxiliary power source, repeating the turn-on and turn-off at the output terminal side of the electric power source, thereby supplying the electric power intermittently from the electric power source to the charging terminal of the electronic device to charge the secondary battery in direct current pulses, and increasing the lower-limit threshold value of the discharge voltage of the auxiliary electric power source in response to an elevation in temperature of the fuel cell.