Patent ID: 7911185

Claim:
A battery voltage detection circuit comprising: a first capacitor; an operational amplifier having one input terminal to be applied with a reference voltage and the other input terminal connected to one end of the first capacitor; a second capacitor having one end connected to an output terminal of the operational amplifier and the other end connected to the other input terminal of the operational amplifier; a voltage application circuit configured to sequentially apply a voltage of one terminal of a battery and a voltage of the other terminal of the battery to the other end of the first capacitor; a discharge circuit configured to allow the second capacitor to discharge before the voltage of the other terminal of the battery is applied to the other end of the first capacitor; a constant current circuit configured to output a constant current causing electric charge accumulated in the second capacitor to be discharged at a predetermined speed, in response to a discharge start signal input after the voltage is applied to the other end of the first capacitor; a comparator having one input terminal to be applied with the reference voltage and the other input terminal connected to the output terminal of the operational amplifier; and a measurement circuit configured to measure a time period from a time when the discharge start signal is input until a time when an output signal of the comparator changes to one logic level, as a time period corresponding to a voltage of the battery, at least one of the operational amplifier and the comparator being provided with an offset so that the output signal of the comparator changes to the one logic level when the voltage applied to the other input terminal of the operational amplifier is a voltage of a predetermined level lower than a level of the reference voltage.