Patent ID: 6265848
Filing Date: 2001-07-24
Classification: H01M,H02J,Y02E

Abstract:
A battery state monitoring circuit for a portable electronic device, comprising:an external connection terminal connectable to a secondary battery, to an external load driveable by the secondary battery, to an external charger for charging the secondary battery, and to at least one switch element connected between the secondary battery and the external connection terminal;a control circuit for controlling the charge/discharge state of the secondary battery by controlling the on/off state of the at least one switch element; a monitoring circuit for monitoring at least one of a voltage and a discharge current of the secondary battery;a voltage change-over circuit connectable to the secondary battery, the external connection terminal, and the monitoring circuit for supplying a power supply voltage to at least the monitoring circuit by selecting the higher voltage of a voltage at the external connection terminal and the secondary battery voltage;a voltage regulator connected to an output of the voltage change-over circuit for supplying a regulated voltage to at least the monitoring circuit; and a circuit for suspending operation of the monitoring circuit when an output voltage of the voltage regulator is below a predetermined level adequate to ensure stable operation of the monitoring circuit so that the monitoring circuit is operative only when the selected power supply voltage supplied thereto is higher than the predetermined level;wherein the monitoring circuit controls the at least one switch element so that the secondary battery is disconnected from the external connection terminal when the selected power supply voltage is lower than the predetermined level.