Re: Resistor value for LED

On Thu, 28 Apr 2005 16:25:05 -0400, the renowned "mc"
<mc_no_spam@xxxxxxx> wrote:

>
>"Tom" <no@xxxxxxxxxxxxxxx> wrote in message
>news:42712E86.9A60113F@xxxxxxxxxxxxxxxxxx
>>I have a led that needs 2.3 to 2.6 V max, I want to run it off a 5V
>> supply at close to its maximum voltage.
>>
>> The exact led is here:
>>
>> http://tinyurl.com/cmleb
>>
>> Could someone tell me what value resistor I need to use?
>
>Typical operation is with a current of 20 mA. I am surprised that they say
>2.3 volts, because the normal forward voltage drop of a red LED is 1.8
>volts, and that's what I'll assume.

Um, you're assuming the data*** is *wrong*?

I just measured a 635nm red (that's less orange) of similar
brightness, and it came to 2.1V @ 20mA.

Generally, forward voltages seem to be creeping up (for the same color
of emitted light) as efficiencies increase.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
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