In-vehicle equipment
A FET of a power supply reverse connection protection section is connected between a battery and an electronic device, and at a time of reverse connection of the battery, the FET is turned off and a parasitic diode of the FET prevents a current flowing in a direction opposite to a direction at a time of normal connection. A transformer is used in a DC/DC converter of a first power supply section that supplies power to a control section, and a voltage generated in a secondary winding is applied to the FET.
1. In-vehicle equipment comprising:
an electronic device that operates using an in-vehicle battery as a power supply;
a first power supply that has a step-down DC/DC converter to reduce a voltage of the battery;
a controller that operates using the first power supply as a power supply to control the electronic device;
a power supply reverse connection protector that has a FET connected between the battery and the electronic device, wherein the FET is connected such that a forward direction of a parasitic diode of the FET matches a direction in which a current flows at a time of normal connection at which the battery and the electronic device are connected with a positive polarity, and that at a time of reverse connection at which the battery and the electronic device are connected with a reverse polarity, the FET is turned off and the parasitic diode prevents a current flowing in a direction opposite to that at the time of the normal connection; and
a second power supply that generates a drive voltage to turn on the FET of the power supply reverse connection protector at the time of the normal connection by using a voltage generated in the step-down DC/DC converter of the first power supply.
2. The in-vehicle equipment according to claim 1 , wherein
the second power supply has a second coil added to a first coil constituting the step-down DC/DC converter of the first power supply, and outputs a voltage generated in the second coil to the FET of the power supply reverse connection protector as the drive voltage.
3. The in-vehicle equipment according to claim 1 , further comprising a semiconductor switch that switches between energization and interruption to the electronic device from the battery, between the FET of the power supply reverse connection protector and the electronic device or between the battery and the FET of the power supply reverse connection protector, wherein
the semiconductor switch operates with the drive voltage generated by the second power supply.
4. The in-vehicle equipment according to claim 3 , further comprising a signal transmitter that transmits the drive voltage generated by the second power supply to the semiconductor switch, wherein
the signal transmitter has an integrator that slows down a switching operation of the semiconductor switch.
5. The in-vehicle equipment according to claim 3 , wherein
the FET of the power supply reverse connection protector and the semiconductor switch that switches between energization and interruption to the electronic device from the battery are integrally configured.
6. The in-vehicle equipment according to claim 1 , wherein
the electronic device is constituted by an LED and an LED lighting device that lights the LED.