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Author Topic: Using an Unknown LED  (Read 1476 times)
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How did you deal with possible reverse polarity connection to the led? (retorical question, you didn't deal with it per your drawing)  smiley-wink

 Most standard leds have a maximum reverse voltage rating of only 5vdc. An internal series diode in series with the test leads output would probably be enough.

Lefty

As you can see from the drawing, I do not deal with reverse polarity. But, since the current is limited to approximately 20 mA, who cares if the LED reverse conducts? Won't hurt it.
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since the current is limited to approximately 20 mA, who cares if the LED reverse conducts? Won't hurt it.

You don't think the voltage would play a role here?
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I've burned out exactly one LED from reverse voltage.  It so rarely happens, it took me a while to figure out why it no longer worked.  Oddly enough, it was a PCB-mount LED that was capable of handling over 50mA, and bright enough that you don't want to look at it for long.  I would've figured it would be pretty tough to kill.  But, of all the 3mm and 5mm LEDs I've ever messed with, I have yet to ruin one with a current limiting resistor in place.  Not to say it can't happen, but I don't even try to avoid reversing them if I don't have a way of knowing ahead of time.  At 5v, anything from 220R to 10K is likely to suffice, at least for a test.
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