On Wed, 05 May 2004 02:46:06 +0000, Ernest Christley wrote:

anonymous coward wrote:
Have you considered using a constant current regulator, instead of a
resistor? I believe there is an example circuit given in the LM337/317
datasheet showing how to build one using only the LM337 (normally used as
a voltage regulator) & one resistor.

It would need to be bolted to a heatsink, like the Luxeon Star LEDs, but
IIRC the LM337 and cousins also shut down if they overheat.

AC


Yes. I considered it. I opted for the simplicity of a single current
limiting resistor and the constant voltage regulator that is already
there. Number one rule of fault management. If it ain't there, there's
no way to break it. Regulators not only add an additional active
component with its list of failure modes, it also adds severl solder
connections and more heat,

A regulator will produce no more heat than a resistor passing the same
current with the same voltage drop. The ones I'm thinking of are 'in-line'
devices, so their (negligible) supply current does not have to be factored
in as an extra source of heat.

I buy what you're saying about complexity, but you would probably only
need a single current regulator + one resistor for each parallel bank of
series LEDs (eugh, but I can't think how better to put it).

BTW, do you need to use zener diodes / transorbs with aircraft power
systems as you do in cars, to avoid problems with voltage spikes?

AC

making it even more difficult to rig the system into a 1/4" piece of plexiglass.