Patent ID: 7952330

Claim:
A protection circuit for a secondary battery, comprising: a first and a second connection terminals for connecting a charging device for charging the secondary battery and/or a load device driven by a discharge current from the secondary battery; a third and a fourth connection terminals connected with the opposite electrodes of the secondary battery; a heat-sensitive switch that is provided between the first and third connection terminals and turned off in the case of exceeding a specified temperature set beforehand; a first heater for heating the heat-sensitive switch; and a protection controller for turning the heat-sensitive switch off by causing the first heater to generate heat if a physical quantity relating to the characteristic of the secondary battery exceeds a preset value of the physical quantity, wherein the heat-sensitive switch is turned off in the case of exceeding a specified operating temperature by self-heat generation due a current flowing thereinto and in the case of exceeding the operating temperature by being externally heated, and the protection controller includes: a switching device for controlling the energization of the first heater, a first overcharging protector for causing the switching device to energize the first heater if a voltage between the third and fourth connection terminals exceeds a specified overcharging protection voltage, and a second overcharging protector for causing the switching device to energize the first heater if a voltage between the first and second connection terminals exceeds the overcharging protection voltage, wherein the first overcharging protector includes a first comparator for detecting whether or not a voltage between the third and fourth connection terminals exceeds the overcharging protection voltage, the second overcharging protector includes a second comparator for outputting a high-level signal if a voltage between the first and second connection terminals has exceeded the overcharging protection voltage, and the switching device energizes the first heater if at least either one of the first and second comparators has outputted a high-level signal, wherein the switching device includes: an OR gate having an input terminal thereof connected to output terminals of the first and second comparators; and an n-channel field-effect transistor having a gate thereof connected to an output terminal of the OR gate, having a drain thereof connected with the first heater, and having a source thereof connected to the second and fourth connection terminals.