Patent ID: 7528578

Claim:
A power supply apparatus, comprising: a battery pack including a plurality of rechargeable batteries connected in series; and a charge circuit charging the battery pack, the battery pack including, a discharge current interruption FET which is connected to the rechargeable batteries in series and cuts off the discharge current, and a minimum voltage detecting portion which compares the voltage of each rechargeable battery with a minimum voltage, and switches the discharge current interruption FET from ON state to OFF state to cut off the discharge current when the voltage of any rechargeable battery becomes lower than the minimum voltage, and the charge circuit including, a charge current switching portion which detects the output voltage of the battery pack, and switches the charge current so as to charge the battery pack in a main charge mode when the output voltage is higher than a prescribed voltage, and to charge the battery pack in a preliminary charge mode with a current smaller than that in the main charge mode when the output voltage is lower than the prescribed voltage, wherein the battery pack and the charge circuit are connected with a signal line which transmits an OFF signal representing OFF state of the discharge current interruption FET to the charge current switching portion, and the charge current switching portion charges the battery pack in the preliminary charge mode in a state where the voltage of any rechargeable battery becomes lower than the minimum voltage and the OFF signal is provided from the signal line, and even in a state where the output voltage of the battery pack as a whole is higher than the prescribed voltage.