Patent ID: 7663375

Claim:
A battery voltage detecting circuit comprising: a first operational amplifier; a first capacitor having one end connected to one input terminal of the first operational amplifier; a second capacitor having one end connected to an output terminal of the first operational amplifier and the other end connected to the one input terminal of the first operational amplifier; a third capacitor having one end connected to the other input terminal of the first operational amplifier; a fourth capacitor having one end applied with a reference voltage and the other end connected to the other input terminal of the first operational amplifier; a first switching circuit configured to apply a voltage of one terminal of a battery to the other end of the first capacitor and to apply a voltage of the other terminal of the battery to the other end of the third capacitor; an energizing circuit configured to be energized with a transient current flowing into the first capacitor, when the voltage of the one terminal of the battery is applied to the other end of the first capacitor; a second switching circuit configured to electrically disconnect the one input terminal of the first operational amplifier from the one end of the first capacitor while the transient current is flowing, and to electrically connect the one input terminal of the first operational amplifier to the one end of the first capacitor after the transient current has stopped flowing; a discharging circuit configured to discharge the second and the fourth capacitors; and a third switching circuit configured to apply a voltage of the other terminal of the battery to the other end of the first capacitor after the one input terminal of the first operational amplifier and the one end of the first capacitor have been electrically connected to each other and the second and the fourth capacitors have been discharged, the voltage of the battery being detected based on the voltage of the output terminal of the first operational amplifier after the voltage of the other terminal of the battery has been applied to the other end of the first capacitor.