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re RE: lights (nay audi content)

"James M. De Arras" <jmd@westlab.com> responded:

Best thing would be a constant current source, I'm not sure if they make
them in the needed range, but they had 1.2ma ones a decade ago, so they
ought to have them.


 -----Original Message-----
From: 	Bob Virtual [mailto:hey9811@yahoo.com] 
Sent:	Thursday, November 11, 1999 12:56 AM
To:	Audi q list
Subject:	lights (nay audi content)

I'm thinking of replacing the incandecent light bulbs
with LEDs. The only thing I planned was putting in a
simple resistor per LED. But how well does that cope
with the flucuating voltage, power surges & spikes,
etc., that come with automotive electrical system?
I replace Audi's LEDs in the window switches with Radio Shack miniatures
with 1 kohm in series.  This sets the current to roughly half its rated
current.  Unless you get spikes above 20 volts, they should be safe.  None
of mine have burned out yet.

As I vaguely recall, you can connect gate and source of certain FETs to
generate a current source.  Union Carbide (I think) long ago and far away
used to sell current-limiting diodes of this type.  You might have to
experiment to get the value you want, unless these are still available from
someone (Motorola?).  Hand constructed ones from FETs would take up a lot of
room in the switches.

Kirby A. Smith   New Hampshire USA
1988 90q Titanium gray, 182 kmi
1988 90q Stone gray, 187 kmi 
1995 S6 Pearl effect, 82 kmi