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Re: Resistors for LEDs: the real answer

That's great info, thanks! I *am* using DC and the LED *is* rated at 2 volts and 20 mA.

Your detailed explanation is much appreciated. The Tomar instructions and several books I own on model railroad electronics are vague and do not really make things clear when it comes to resistance. Now I have deeper understanding that I can apply to any future situation.

Thanks to all!

craig

In the thread above where someone asked about selecting resistors for use > with driving a LED, nobody really nailed it right on the head. So just to > clear a few things up, a rather long post follows. > > >
Reply to
Biff
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Biff skriver:

In most cases is 5-10mA sufficient to drive the LED...

KLaus

Reply to
Klaus D. Mikkelsen

Ray, Since this comes up all the time, and since not everyone has the Mr. Wizard formulas memorized, yes, I would say that was necessary - and useful. If details bother you skip them and just see if smoke comes out. Personally, with white LEDs at $2.50 each or more, I'd do the math first because those itty-bitty PN junctions are one hell of a lot less forgiving than Atlas snap relays. As we used to say, the diode fails in order to protect the fuse. Not everyone uses their stuff the same way. Suppose you were powering some interior lights from one of those cute 6 volt batteries for garage dorr openers. Real quick now, what resistors would you use for a red LED and a white LED in that circuit? Or, it you are using an LM7805 regulator for constant brightness lighting - which resistors then? This description obviously wasn't aimed at you, and you don't care. So what? Others do. Thanks Dave, useful stuff. Gee, I was thinking about posting my streetcar stop light circuit that goes on when the car stops and off when it moves, but I guess Ray can do that - right?.

Reply to
snert

On Tue, 05 Sep 2006 16:54:53 -0700, I said, "Pick a card, any card" and David Nebenzahl instead replied:

Do explain why you chose to move this to a new thread. I'm sure that the answer is obvious. I disagreed with you.

-- Ray

Reply to
Ray Haddad

THANK YOU!!!! You made it easy to understand. Paul in Fl.

Reply to
cfseven

Excellent explanation!

I wish I had your type of teach> In the thread above where someone asked about selecting resistors for

Reply to
dmtaurus

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