To provide a protection circuit that is the most suitable for protection of electronic control unit (ECU) during reverse connection of a power supply.
In ECU45 operating on a power supply of a battery 3, n-channel FET21 is provided on a power supply wiring 15 that establishes a connection between a power supply terminal 5 connected to a plus terminal of the battery 3 and a control circuit 13 for power supply, in such a manner that an anode of its parasitic diode D1 is situated at the side of a power terminal 5. Further, n-channel FET22 is provided at a downstream side of the FET21, in such a manner that a cathode of its parasitic diode D2 is situated at FET21 side. When an ignition key switch 9 is turned on during normal connection of the battery 3, FET's21, 22 are turned on by charge pump circuits 43, 47 to which operating electricity is supplied from a drain side of FET21, and electricity of a battery 3 is supplied to the control circuit 13. Further, FET's21, 22 are turned off during reverse connection of the battery 3, and thus reverse current is inhibited by the parasitic diode D1.
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YUKAWA HOSHO
MAEDA SHINICHI
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