Car Headlight Control

  
It is annoying to realize that you have left your car headlights on only to find that the battery is flat. One possib
Car Headlight Control - schematic

le way to prevent this is with the present control. The circuit does not provide a warning, but an action: when you switch off the ignition, relay Rel is de-energized and the headlights are switched off—unless you deliberately decide otherwise. That decision is made possible by switch SI, which, when operated, triggers silicon-controlled rectifier Thl so that Rel is energized. Notice that this is possible only when the ignition switch, S2, is off. Otherwise, the voltage across Thl is so low, owing to shunt diode Dl, that it cannot be triggered. However, the headlights should not normally be switched on when the ignition is off; in most cases SI will be used only rarely and the switch can then be omitted altogether. The relay should be a standard 12-V car type with contacts that can switch up to 25 A.




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