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LED Resistors Answered

I`ve been searching around everywhere about Resistors and how to use them, I understand that they resist power to the LED light t to a safe limit, but I need a noobs guide on how to use them, can someone help me?

4 Replies

guyfrom7up (author)2008-07-30

Well, to light up an LED search for LED calculator, if you actually want to know how to use them with a formula, here' the following info I typed in another form

Here's a run down on LEDs

Minimum voltage to light (voltage drop):
Orange/Yellow - 2
Green - 2.1
White/Blue - 3

How to determine the resistor (formula):

Voltage input - Voltage drop X 50 = Resistance in ohms

(BTW the x 50 comes from 20mA LEDs take, 1/0.02 = 50, and it's easier to do that than a small divide)

Example, power source is a 9 volt lighting up one red LED
9-1.7 = 7.3
7.3 x 50 = 365
you need a 365 ohm resistor, give or take some, you don't have to be super exact with the resistor

Another example
source is a 12 volt wallwart
lighting up 3 white LEDs in series
12-3-3-3 = 3
3 x 50 = 150
you need one 150 ohm resistor in series with 3 white led's when the power source is 12 volts.

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Alcreion (author)guyfrom7up2008-07-30

Very useful information, but how to i connect resistors too?

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guyfrom7up (author)Alcreion2008-07-30

well, you just put the resistor in series if you have multiple LEDs in parallel, each set of parallel MUST have their own resistor. You can't just have one resistor driving a couple of LEDs in parralel

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