I'm curious about what happens to an LED when it is exposed to a moderate overcurrent situation.
This question came about as I was troubleshooting some small white LED lights I built using 3 5mm LEDs and a current limiting resistor to run on 12Vdc (supplied by a lead-acid battery charged by solar). After some time, many of these strings would start to flicker or blink.
I was about to post a question about that, when I redid my resistor calculation. I had originally calculated that a 100 ohm resistor would be sufficient to keep the current around 20mA (assumed 12.5V -
10.5V total LED drop). But on recalculation, that would result in 30mA (the absoulte maximum rating) at 13.5V, the low end of charging range. Adding another 47 ohm resistor seems to have helped.So now I'm curious what happens inside the LED when the current exceeds the absolute max current by a modest amount (i.e., not the obvious overcurrent of leaving out the resistor entirely). The LEDs I'm using seem to return to normal operation when the current is reduced, and seem to produce a momentary open-circuit condition during overcurrent, presumably from overheating.
Anyone know what's happening to the semiconductor material in this situation?
Thanks,
--Andrew