Patent ID: 7072164

Claim:
An electric parts drive circuit comprising: a first field-effect transistor including in parallel a first parasitic diode for allowing an electric current flow into a plus line and provided between the plus line to be connected to a plus terminal of a battery and an electric part; a second field-effect transistor for reverse connection protection including in parallel a second parasitic diode for allowing an electric current flow from the first field-effect transistor into the electric part, the first field-effect transistor and the second field-effect transistor being connected in series in order from the plus line to the electric part; a third field-effect transistor including in parallel a third parasitic diode for allowing an electric current flow into the electric part and provided between a minus line to be connected to a minus terminal of the battery and the electric part; a failure diagnosis switch unit for switching between conduction and shutoff between a drain of the second field-effect transistor and the plus terminal of the battery; and a switch control unit for controlling switching between conduction and shutoff of the first to third field-effect transistors and the failure diagnosis switch unit, wherein the switch control unit diagnoses a failure of the second field-effect transistor based on the voltage between the first and second field-effect transistors responsive to switching between conduction and shutoff of the second field-effect transistor in a state that the first and third field-effect transistors are shut off and the failure diagnosis switch unit is brought into conduction, wherein the failure diagnosis switch unit includes: a PNP transistor having a collector connected via a first resistor between the plus terminal of the battery and the drain of the second field-effect transistor; second resistors and an NPN transistor connected in series between the plus terminal of the battery and ground; and third resistors connected in series between the switch control unit and ground, wherein a connection point of the second resistors is connected to a base of the PNP transistor and a connection point of the third resistors is connected to a base of the NPN transistor.