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# Resistor for SMD LED 1306? Answered

I'm struggling to find any clues of what kind of resistor to use as I am a little new at this kind of project. I'll be using the lights in a small scale 9v project for up to 100 SMDs.

I'd appreciate any advice!

Cheers :)

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## 5 Replies

Downunder35mBest Answer (author)2015-02-20

You need to know the max current of the LED and the rated voltage for the LED.

9V - LED Voltage / current of the LED = Resistor value.

As a personal rule of thumb I prefer to stay slightly under the max rating for LED's to increase their lifespan.

As an example:

Voltage for the LED assumed to be 2.3V and a max current of 15mA:

(9V - 2.3V) / 0.015A = 447Ohm

At 470Ohm it will be 14.25mA

At 500Ohm for the resistor the current will be reduced to 13.4mA

Next higher standard value would be 560Ohm and 12mA

Wired_Mist (author)2015-02-21

If you are running up to 100 of these led's why not wire them in Series?

Wire a group of three LED's in series with a 150-Ohm resistor !

Downunder35m (author)2015-02-20

How else do you want to write it correctly with no unicode supported?

This is the way it way always done ;)

Without access to grrek symbols here it has to do.

-max- (author)2015-02-20

I would assume they will work plenty bright at 15mA, so I would use that figure, then you need to know how much voltage drop across the LED is to figure out the perfect resistor. You can do that with a potentiometer and a few multimeters, (to measure voltage and current simultaneously) or just refer to the datasheet for the numbers.

-max- (author)2015-02-20

You can always just use a 1K resistor. That will be fine.

In this video, I have included a guide about 2/3rds the way through a guide on calculating the exact resistor to use to get the most power out of the LED without overdriving it.