Re: Hooking up 2 LED's to 25v flasher. What resistor to use on the negative side?

Here's a little Excel spreadsheet that can be used to calculate
the resistor value for any LED on a DC power source.

Just plug in the supply voltage and the current that you want to
pass through the LED (default value is 20 milliamps).

The spreadsheet also calculates the power dissipation of the
series resistor. In many cases, the dissipation may be well
above what the typical 1/4 Watt resistor can handle.

The calculation also takes into account the effect of a 1N400x
series diode, but if it's not used, just set its voltage drop from
the default 0.7 Volts to 0.

Here's the link to the file: http://pinballpal.com/led.xls

-Mark
--
http://pinballpal.com/

"Ken S" < ksweek@xxxxxxxxxxxxxx> wrote in message news:6iots118l7f39com065j6m7n5u9fl5dflr@xxxxxxxxxx
> With that high a supply voltage and only 2 leds you have close to a
> constant current situation. In other words, it won't make much
> difference what voltage your leds require as it won't change current
> much for a given resistor. Example; If you used a 1000 ohm resistor
> and two 2.2v leds and a 25 volt supply, current would be a little
> under 22 ma. With 3.3 volt leds and same resistor current would be a
> little over 18 ma.
>
> Ken S
>
>
> On Wed, 18 Jan 2006 21:16:32 +0100, Aeneas <averhe@xxxxxxxxx> wrote:
>
>>On 18 Jan 2006 12:06:18 -0800, "Cayle George" <caylegeorge@xxxxxxxxx>
>>wrote:
>>
>>>easiest thing to do is to buy a new set of leds to put in there that
>>>you know the values of.
>>>
>>>Otherwise, it is probly a 3 or 3.3 volt led.
>>
>>My thought too.. he opened up the thing already, so just remove the
>>pcb and leds and put in new ones you know.
>>
>> Aeneas.
>>-- http://www.flippers.be
>


.

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