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LED wiring

G

Gustavus

Limp Gawd
Joined
Jan 19, 2004
Messages
224
I need to know the *blank* ohm resistor to get for a 3v LED that has a 12v current coming into it
 
http://linear1.org/ckts/led.php

You're really confused about terms.

You need to know the LED's forward voltage at a given current (which is usually 20 mA) and the supply voltage.

Current is measured in Amps, or milliamps.

Try the calculator with:
12V supply voltage
3.3 V diode forward voltage (for blue or white, that's a typical value)
20 mA diode rated current

If you have some other color of LED, 3V is too high a drive voltage in all likelihood.
 
Take (12 volts - forward voltage of LED)/current


example: blue LED has 3.3v forward voltage (max), 20mA

resistor you need = (12 -3.3)/0.02 = 435 ohms, so pick like 450 ohms and you're good to go.
 
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