Patent ID: 8072189

Claim:
A charge and discharge control circuit formed on a second-conductivity-type substrate, for controlling charge and discharge of a battery including a second-conductivity-type first MOS transistor and a second-conductivity-type second MOS transistor which are provided on a charge and discharge path, the charge and discharge control circuit comprising: a detection terminal for detecting that a charger is connected to the battery with polarities thereof being reversed to polarities of the battery; and a charger reverse connection detection circuit comprising: an input terminal provided to the detection terminal; an output terminal; a first parasitic bipolar transistor including a second-conductivity-type base provided to a first power source terminal and a first-conductivity-type emitter provided to the input terminal; and a second parasitic bipolar transistor including a first-conductivity-type base provided to a first-conductivity-type collector of the first parasitic bipolar transistor, a second-conductivity-type emitter provided to a second power supply terminal via a resistance component, and a second-conductivity-type collector provided to the first power supply terminal, wherein the charger reverse connection detection circuit, when a voltage of the input terminal is equal to or higher than a voltage determined by adding a threshold voltage of a diode to a power supply voltage, operates so as to turn on the second-conductivity-type first MOS transistor which is turned on to cause a charge and discharge current to flow and is turned off to cause only a discharge current of a first parasitic diode to flow, and operates so as to turn off the second-conductivity-type second MOS transistor which is turned on to cause the charge and discharge current to flow and is turned off to cause only a charge current of a second parasitic diode to flow, to stop the discharge of the battery.