Abstract: A charging-and-discharging device in an electronic apparatus includes a rechargeable battery and a charging device for charging the battery. The charging-and-discharging device includes a switching circuit electrically isolating one terminal side of the battery from a ground side of the electronic apparatus. The charging-and-discharging device further includes a charge control section controlling the isolating of the one terminal side of the battery from the ground side of the electronic apparatus by turning off the switching circuit during charging of the battery. In the charging-and-discharging device, the one terminal side of the battery is isolated from the ground side of the electronic apparatus by the switching circuit during charging of the battery and a closed loop including the charging device and the battery is established to charge the battery.

Abstract: A booster type DC-DC conversion circuit and a voltage reduction type DC-DC conversion circuit are connected in series with a battery. When battery voltage is high, the booster type DC-DC conversion circuit does not operate, and the voltage reduction type DC-DC conversion circuit outputs a constant voltage lower than the battery voltage. When the battery voltage drops, the booster type DC-DC conversion circuit operates, and converts the battery voltage to a constant voltage higher than the operation voltage of the voltage reduction type DC-DC conversion circuit. The voltage reduction type DC-DC conversion circuit outputs a constant voltage. The power supply apparatus can continuously output a constant voltage from when the battery voltage is high until it becomes low, and can efficiently utilize the battery capacity.