Richard Rasker wrote:
Joerg wrote:

Richard Rasker wrote:
Spehro Pefhany wrote:

On Wed, 09 Sep 2009 20:55:49 +0200, Richard Rasker
wrote:

Jan Panteltje wrote:

On a sunny day (Wed, 09 Sep 2009 20:02:38 +0200) it happened Richard
Rasker wrote in
et:

So my question: is this a simple case of "bad luck", or are there
other ways a LED in an opto-isolator may fail in this weird way
(current OK, yet no light)?
Perhaps some part internal to the opto-isolater did break of due to
vibration and blocks the light path?
Did you open the defective one?
No, I didn't (yet) -- but isn't this very, very unlikely?

Richard Rasker
It's incredibly likely compared to what seems to be the only
alternative- an LED which acts exactly like a AlGaAs D but doesn't LE.

OTOH, an electrically damaged diode that measured something like a
short would not be unusual at all. Could be something like lightning
or RF damage. You don't have the opto in there because it's a benign
environment, eh?
Hehe, spot on -- this is a 24V ship's electrical installation, with heavy
DC motors and other possible sources of interference. That's why I also
use DC-DC-couplers (with a wide-range input) to supply the rest of the
circuitry. That way, input, output and supply are all galvanically
separated.
But the LED still behaves as a LED -- in an electrical sense, that is.
It's not shorted out or anything.

Here is a short article about LED failure modes:

http://www.emsnow.com/cnt/files/Whit...EDFailures.pdf

I am no expert on this but have done a fair bit of work with laser
diodes, including ones in the $1k class. It only takes microseconds of
mishap and a $1k laser diode becomes a $1 LED. We also had cases where
the diode looked quite normal electrically but only a miniscule or
absolutely no optical energy was generated by it anymore.

OK, thanks, this is quite interesting. For the time being, I'll just wait
and see if this failure repeats itself (and try to be even more careful
handling and soldering the devices).


Reminds me of a joke. No, no, this is _not_ meant to apply to your case.

A bowling group returns from a road trip. Coming down a pass the brakes
on the car fade. 40mph ...50 ... 60 ... some guys start to scream. The
driver steers towards the guard rail, lots of sparks fly, some more
screaming, a passenger faints, vehicle scrapes to a stop, all smoking.
Everybody evacuates. One guy, an engineer, looks at the mess: "Tsk, tsk,
tsk, unbelievable. Interesting. Hey, let's take it up back to the top
and see if the failure repeats itself!"

--
SCNR, Joerg

http://www.analogconsultants.com/

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