Electric parts drive circuit
An electric parts drive circuit has: a first field-effect transistor including in parallel a first parasitic diode and provided between the plus line and an electric part; a second field-effect transistor including in parallel a second parasitic diode, the first and second field-effect transistors 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 and provided between a minus line and the electric part; a failure diagnosis switch unit; and a switch control 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.
1. 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.
2. The electric parts drive circuit as set forth in claim 1 , wherein the electric part is a solenoid in an electromagnetic valve of a brake fluid pressure controller for a vehicle.
3. An electric parts drive circuit, comprising:
a first field-effect transistor including in parallel a first parasitic diode;
a second field-effect transistor for reverse connection protection including in parallel a second parasitic diode;
a third field-effect transistor including in parallel a third parasitic diode;
wherein the first field-effect transistor, the second field-effect transistor, an electric part, and the third field effect-transistor are connected in series between a plus terminal and a minus terminal of a battery;
a failure diagnosis switch unit 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 field-effect transistor, the second field-effect transistor, the third field effect-transistor, and the failure diagnosis switch unit,
wherein the switch control unit diagnoses a failure of the second field-effect transistor.
4. The electric parts drive circuit as set forth in claim 3 , 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.
5. The electric parts drive circuit as set forth in claim 3 , wherein the electric part is a solenoid in an electromagnetic valve of a brake fluid pressure controller for a vehicle.
6. The electric parts drive circuit as set forth in claim 3 , wherein the switch control unit diagnoses a failure of the second field-effect transistor based on a voltage between the first and second field-effect transistors.
7. The electric parts drive circuit as set forth in claim 3 , wherein to diagnose a failure of the second field-effect transistor, the switch control unit shuts off the first and third field-effect transistors and brings the failure diagnosis switch unit into conduction, and switches the second field-effect transistor between conduction and shutoff.