AVR-Chat

Bryan Martin wrote:
> Quick question, I am trying to start a simple mini IR LED array but
> second guessing myself. 
> 
> IR LED Info:
> Forward Voltage: 1.2V (max 1.6v)
> Forward Current: 100mA (max 1.2A)
> 
> I am hooking 4 LEDs direct to 12V DC power in series w/a resistor of
> 81ohms. 
> Thing is the resistor is getting like really really hot.  I dont mean
> warm I mean hot.  Am I ok?  Second question is I want to add an
> additional 4 LEDs. Would it be better to run this like below and go
> w/2 X 4 LED series or move to 8 LEDs w/a different resistor?  
> 
> I got my figures for the resistor as follows if it matters:
> 
> 1.2v per LED * 4 LEDs = 4.8v drop
> (12v - 4.8v drop) / (100 / 1000) = 72 ohms
> 

Power dissipation in the resistor = I^2 x R = 0.1^2 x 81 = 0.81W

So it will get hot... Make sure your resistor is at least a 1 watt type

-- 
Tim Mitchell
tim@sabretechnology.co.uk http://www.sabretechnology.co.uk
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