Patent ID: 8618774

Claim:
A battery state monitoring circuit for controlling charge/discharge of a secondary battery, comprising: a reference voltage circuit; an overdischarge detection circuit for comparing a voltage of the secondary battery with a voltage of the reference voltage circuit, to detect overdischarge of the secondary battery; a control circuit for receiving an output of the overdischarge detection circuit; and a minimum operating voltage monitoring circuit for detecting a minimum operating voltage of the battery state monitoring circuit, wherein the minimum operating voltage monitoring circuit comprises: a first transistor for detecting that the voltage of the secondary battery is lower than the minimum operating voltage of the battery state monitoring circuit; and a second transistor for setting the output of the overdischarge detection circuit to an overdischarge detected state when the voltage of the secondary battery is lower than the minimum operating voltage of the battery state monitoring circuit, wherein the second transistor comprises a gate in communication with the control circuit, a drain coupled to an output of the overdischarge detection circuit, and a source coupled to one of a negative terminal of the secondary battery or a positive terminal of the secondary battery.