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Last Updated on: Tuesday, June 01, 2021 03:06 PM

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More  Automotive CircuitsSwitches

Car Ignition 12v Switch

A Discover visitor needed a way to redirect +12v DC in his car to some auxiliary loads whenever the carís engine was running.  Many cars have cigarette lighter outlet jacks, which are either live all the time or become live when the carís engine is running.

The visitor wanted to plug a device into a full time live outlet but only switch on when the carís engine was running. The circuit below performs this function.  It relies on the fact that the carís battery voltage increases from about 12.5v in standby mode to 14 volts whenever the engine is running.  When the voltage is above 13.5v, the circuit switches on a p-channel MOSFET.  The circuit uses a common LM393 dual voltage comparator and a 10v 5% zener diode as a voltage reference.

Click on Circuit Below to view PDF of Schematic

Car Ignition 12v Switch designed

 by David Johnson

More  Automotive CircuitsSwitches

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