resistor

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retfiredog

Joined Mar 7, 2007
2
I am not a electronic guru and need help on probably something simple. I am running a 12dc line and off of that ,a series of 3-4 5mm led's. Question is what resistor to go from 12v to 3v?:confused:

retfiredog
 

Papabravo

Joined Feb 24, 2006
14,441
Each LED will have a forward voltage drop which depends on its color, not its size. If the leds are in series you need to add this number. If they are in parallel and are different colors this could be problematical. In any case subtract the forward voltage drop(given in the datasheet) from 12V. Divide this voltage by the current you want to go through the LEDs and that will be the resistance in ohms.
 

beenthere

Joined Apr 20, 2004
15,819
LED's need to have the current through them held to a limit. Volume 3, chapter 3 of the E-book on this site will give you the means to calculate the proper resistor for your application.
 
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