I remember playing with signal LEDs and observing what happens when I misuse them, and one particular LED behaved very strangely, as if it were stateful.
Using a drained 9V battery (that can only deliver about 100-200 mA), the (probably green) signal LED and a tester, I remember observing the following cycle:
- I apply the current forward, the LED shines dimly, current is rather constant (5-15 mA?)
- I apply the current backwards, the LED obviously does not emit any light and the meter showed small, but raising current (beginning under 1mA)
- The current keeps raising and suddenly spikes (50-100 mA?), as if the LED is almost short circuited
- I reverse the polarity again. The same relatively high current flows in other direction, no light is emitted. But the current slowly decreases.
- Suddenly the current drops to about 5-10 mA and the LED starts emitting light again (first dim, then a bit brighter).
- The more time the LED is turned on "normally", the more time of reverse 9V needed to trigger the breakthough. The more current flowed backward, the more forward-flowing time needed to "repair" the LED.
It didn't look like as if it were just temperature. If I waited a bit the "state" preserved.
How can this stateful behaviour be explained? What happens when current flows backwards though LED? Why could it be "healed" by forward current?