Unstable LEDs

Hello,

So I was working with LEDs and at 3.3V (Which is what I usually use) one of my LEDs blew up. I tested them, and I had some burnt out which probably happened before, but all of my yellows and reds started smoking and becoming unstable the second I put some power. Why is this.

Any help solving my problem will be greatly appreciated.

You were using current-limiting resistors, or a constant current source, right?

At first I forgot to put in a resistor for 3.3 Volts, but that works fine for me normally. Later when re-testing they still were smoking and almost blowing so I had to cut off power. It seemed specific to red and yellow.

The LEDs came with my Uno and I use the Uno as the power source. This has never happened to me before, and I want to figure out my problem so it doesn't happen again.

Red, Yellow and Orange LEDs have a lower forward voltage drop of about 2.1-2.2V so if you try to drive these with 3.3V without any current limiting they will burn out. Other colours have a forward voltage of about 3.2-3.4V so they are far less likely to burn out. You should always use a series resistor to limit the current.

Do you know what a fuse is? You created a nice colorful expensive fuse with your LED by avoiding Ohms Law. A conducting LED is not a huge difference from a wire (with a sense of direction).

So I was working with LEDs and at 3.3V (Which is what I usually use)

So you find out the hard way that what you were doing was not OK.

Read this:-
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html

I've worked with electronics since before LEDs existed (or at least since before they were available) and I remember when they only came in red. I've NEVER seen an LED smoke or blow up, although I probably could do it if I tried.

I've occasionally seen dead-on-arrival LEDs that never light-up, and I've occasionally seen (obviously defective) LEDs that quit working after a few hours or days. Other than that, they essentially last forever (in a properly designed circuit).

I too have never managed to make LEDs smoke or blow up (and I drive 150W led arrays - and really, too many LEDs of all descriptions - with CV!).

I've burned LEDs out a bunch of times times (oddly enough, never one of the above mentioned improperly driven arrays!), but never managed to make them smoke or blow up. How the hell much current was your supply trying to ram through them?! And how did the LED survive long enough make smoke? I'd expect them to fail well before they started smoking...

DrAzzy: And how did the LED survive long enough make smoke? I'd expect them to fail well before they started smoking...

They didn't smoke instantaneously, they either sparked then smoked or blew up. If you really want to, take a small LED (red or yellow) and plug it directly into your arduino's GND and 3.3V (5V might work better) which is what I stupidly did.

At least now I know that other LEDs can handle it but I have to be more careful with red and yellow which I ran out of by fusing them all.

I guess I will have to use an RGB LED until I get more.

Never run indicator LEDs of any color without a series resistor. It is sheer luck that some blue LEDs will work that way without burning out - other brands may not, the life may be shortened, or they may work okay at room temperature, but destroy themselves on a hot day (the forward voltage drop of an LED drops as temperature increases)

Not to mention, if you're driving them off an Arduino pin, you're liable to blow the pin too.

If they do smoke and blow up don't breathe the arsenic-laden smoke, its not a good idea. Better still DTRT and limit the current to at/below 20mA or whatever the max rating is.