Patent ID: 8384355

Claim:
A battery state monitoring circuit for controlling charge and discharge of a secondary battery, the battery state monitoring circuit comprising: a charge/discharge control circuit that is connected across terminals of the secondary battery, for monitoring a voltage of the secondary battery; a charge switch; and a charge switch control circuit for outputting an output signal of the charge/discharge control circuit to the charge switch, wherein the charge switch control circuit operates with a voltage between external terminals of the battery state monitoring circuit, and wherein the charge switch control circuit comprises: a level shifter circuit for converting the output signal of the charge/discharge control circuit into the voltage between the external terminals; a voltage dividing resistor circuit that is connected across the terminals of the secondary battery, for generating a divided voltage; a voltage detection circuit that is supplied with the divided voltage, for detecting a voltage for 0 V charge; and an output circuit that is supplied with respective output voltages of the level shifter circuit and the voltage detection circuit, for controlling the charge switch.