Re: Anybody Seen a Simple LED "Fail-Over" Circuit ?

On 11/26/24 4:00 AM, Bernd Froehlich wrote:

On 26. Nov 2024 at 08:24:12 CET, "186283@ud0s4.net" <186283@ud0s4.net>
wrote:
 

LEDs are great, but never "forever". They DO
fail - but for some safety apps you can't
just HAVE things go black.

 Hmm, just a thought:
If I understood the problem correctly, you want the LED to show some
failstate, right?
 What if you switch the LED on when everything is fine and off would signal
a fail?
 If the LED is off then you know it´s either a fail or the LED is broken.
Either way you have to do something.

   The fail state can (usually) be detected just past the
   current-limiting resistor. If the voltage there suddenly
   equals the supply voltage then the LED is not conducting.
   Again though, more electronics.
   COULD use that elevated voltage to trip a 'relay' trans
   connected to LED-2 however.
   For some apps, you may just be able to look and SEE which
   LED is illuminated. If you normally light the right-side
   one, but peeking in shows the left-side one lit, then
   you have a problem.
   The original LED traffic lights used a cluster of LEDs,
   divided into individually-driven segments. If one failed
   then only a segment went dark, but MOST of them would
   keep working. It was always the greens that went bad.
   TODAY, not sure - I fear they use some more monolithic
   device that'll die all at once.