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### Topic: Calculating LED current (Read 845 times)previous topic - next topic

#### lyron

##### Sep 09, 2012, 10:28 am
I have an infrared LED i would like to control, the datasheet says 5V-100mA but i want to control it with 3.3v.

How do i calculate the current at 3.3v? I knew this once but i forgot.

#### Grumpy_Mike

#1
##### Sep 09, 2012, 10:48 am
Quote

You sure?
You need the forward voltage drop, normally about 1.8V, subtract this from the supply voltage then divide this by the current to get the resistance.
Remember you can only get 40mA from a pin and the 3V3 supply on many arduino modules is limited.

#### lyron

#2
##### Sep 09, 2012, 10:53 am

You sure?
You need the forward voltage drop, normally about 1.8V, subtract this from the supply voltage then divide this by the current to get the resistance.
Remember you can only get 40mA from a pin and the 3V3 supply on many arduino modules is limited.

Made a mistake, Vf = 1.8v, If = 100mA.

I'm not powering this from the arduino's regulator, but a seperate one.

#3