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resistor led calculator

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Reloadron

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Most Helpful Member
A Google of "led calculator download" will bring up several hits. However, most of these calculators are not very good and I do not suggest them. The biggest problem being they don't take into consideration all the aspects and configurations of LED configurations. I suggest you start with the basics (Vsupply - Vled / Iled = Series Resistance) and do your own math. This allows you to consider all the variables for your specific applications.

Ron
 

Pommie

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@Ron,

I'd just like to point out that the brackets (parentheses) are important in this case. So it should be (Vsupply - Vled) / Iled = Resistor. I know that you know this but the OP probably didn't.

Mike.
 

audioguru

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You must understand that E-bay or Chinese websites selling cheap LEDs do not provide a detailed datasheet. They state the forward voltage like it is an incandescent light bulb. They do not state the range of voltages for an LED.

So if you calculate the series current-limiting resistor at the maximum rated voltage for the LED then if the LED actually has a typical or minimum value then its current will be much too high and it will soon burn out.
You should calculate the current-limiting resistor value using the minimum forward voltage of the LED then calculate if its current is high enough using the typical and maximum voltage ratings for the LED.

Some online calculators for the series current-limiting resistor for an LED do not allow enough voltage across ther resistor so they are wrong and cause either a very dim LED or a burnt out LED.
 

Reloadron

Well-Known Member
Most Helpful Member
@Ron,

I'd just like to point out that the brackets (parentheses) are important in this case. So it should be (Vsupply - Vled) / Iled = Resistor. I know that you know this but the OP probably didn't.

Mike.

Thanks Mike. I blew through that early this morning as I was leaving for work and never gave it a thought. My bad on that note.

Ron
 
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