| 摘要 |
PROBLEM TO BE SOLVED: To provide a secondary battery protective circuit which is capable of preventing overcharging of a secondary battery, while using a small mounting substrate. SOLUTION: When a transistor Q1 is not destroyed, charging current Icharge is caused to flow through an on-state resistor RON of the transistor Q1, and therefore there is a voltage drop VDROP (=RON×Icharge ) appearing between the drain and the source of the transistor Q1. When the transistor Q1 is destroyed by shorting, the drain-source resistance of the transistor Q1 becomes zero, and therefore there is almost no voltage drop. Furthermore, since the on-state resistance of the transistor Q1 increases with the increase in temperature but the charging current Icharge remains constant, the voltage drop VDROP increase with the increase in temperature, also. Thus, by detecting whether the voltage drop VDROP of the transistor Q1 is larger or smaller than a specified voltage range, by using a window comparator 151 and a source of reference voltage 152, the destruction or overheating of the transistor Q1 can be detected. When the destruction or overheating of the transistor Q1 detected, the operation of a charger 16 is stopped.
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