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Simple DC circuit with LED, Switch and small Load


New Member
I am building a very simple circuit based on a 12v DC power supply as the power source. The components are shown below.
I would like for the circuit to have a On/Off toggle switch and an LED to indicate when the circuit is powered.
The Circuit powers a 12v DC computer cooling fan.

My presumption is that I cannot (or should not) wire the LED in series so that all the current has to flow through the LED. There must be a simple trick
to have the LED powered when the switch is in the on position without running all the current going to the fan through it?
What is the best way to connect this circuit?



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Most Helpful Member
This is how you'd wire it :-
If Vf is the forward voltage of the LED and ILed is the desired LED current (probably just a few mA for an indicator LED), then the value of R is (12V-Vf)/ILed.


Well-Known Member
Most Helpful Member
A resistor between 1k and 2k ohms should work fine for most indicator LEDs on the circuit above. If the LED is just an indicator to let you know if the fan is running, a diffused LED will work the best.


Well-Known Member
Most Helpful Member
The word you were missing is "parallel". In the #2 schematic, the LED and resistor are in series, and that series string is "in parallel" with the fan.


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