This isn't so much a multiplexing question as it is chemistry.
It's no surprise that giving too much voltage to LEDs can make them explode. However, does somebody know the chemistry behind why they explode? I imagine it's due to the heat being generated by the increasing current which would break down some material in the LED causing them to go into a gaseous state. Eventually the pressure builds so much that the LED explodes. But...what exactly gets changed to gas?
I tried googling this, but it seems the internet is more interested in making LEDs (and caps) explode than explaining why they do so.
I'm sure if you look at Cree on google.....( they are in Raleigh ) as am I, but they are the leading manufacturer for LEDs, it could help you. I had one do so on me too.....big POP sound. A lot of semiconductor elements inside there producing frequency......especially blue LEDs
Im pretty sure that it has everything to do with the LEDs inability to disperse heat, that little plastic body holds the heat in too much. At some point the heat causes expansion, and the heat cant escape well, so the part breaks.
As you try and force more and more electrons to flow through the diode (i.e. a higher current), more energy is dissipated in the semiconductor due to collisions between the electrons and the lattice structure of the semiconducter material. The heat causes the lattice to gain energy and expand.
The plastic doesn't expand as much and so pressure builds up inside the LED until the plastic fails and cracks at which point all the energy stored up pressing against the inside of the shell is rapidly dissipated in the form of pressure waves (sound) and kinetic energy (the bits of plastic launching across the room).
Granted that is a catestrophic failure. In many cases the failure will not be catestrophic, but rather simply the fragile metal wire interconnects will melt rather like a fuse does. Though either way the final outcome is the same... you have to buy a new LED :).
as Tom Carpenter said, the explosion is caused by pressure. Explosions occur when a solid or liquid is rapidly converted to gas. In the case of the LED, I think everything... wire,silicone,plastic, etc becomes volatilized in the energy pulse.
Tom, RPCoyle & Aaron: Thanks for the insight. I never thought about the lattice structure expanding but it makes sense.
I've also sent off an email to Cree to see if I can get any more information. I'll post the reply if I ever get one.
Oh, and Winston, it is pretty tough to make through-hole LEDs explode unless you have something smaller than the standard 5mm ones. It took about 24 V to blow a LED that was about 2 mm in diameter. When I wrote this, I was messing around with SMD LEDs. Those are much easier to explode (even about 0.8 V above the max forward voltage can set it off!)
I must admit I've never had that displeasure...
The only time I ever saw anybody reflexively throw up was a friend who pulled the graphite out of a pencil and connected it to his model train transformer. It burned, he caught a whiff of the smoke and instantly threw up. Good times.