Patent ID: 8159187
Filing Date: 2012-04-17
Classification: H02J

Abstract:
1. An overcharge protection circuit for a secondary battery that is configured by a series connection of a plurality of battery cells and a plus terminal and minus terminal provided respectively on both sides of the series connection, which protects a secondary battery from being overcharged, the overcharge protection circuit comprising: a plurality of voltage followers each constituted by an operational amplifier connected to each midpoint between two adjacent battery cells and serving as a high input impedance element and a NPN transistor connected to the operational amplifier, each of the said voltage followers outputting a voltage of the midpoint as an output voltage; a plurality of excess voltage detection portions each including a first resistance and a shunt regulator, detecting the output voltage from each voltage follower and determining whether the voltage is equal to or higher than a reference voltage indicating an overcharge state; and a charging control portion for terminating charging of the plurality of battery cells when it is determined that the output voltage of the voltage follower detected by the excess voltage detection portion is equal to or higher than the reference voltage, wherein a collector of the NPN transistor is directly connected to an input terminal of an outside power supply via a second resistance, and the voltage output from the operational amplifier is input to a base of the NPN transistor, stabilized by replenishing currents from the outside power supply via the second resistance, and supplied to a ground of the excess voltage detection portion that detects the voltage of each of the second and subsequent battery cells following the minus terminal.