[TR] Converting TR6 rheostat to LED use

[Randall]

> The other issue with the LM317 is
> that it is not very efficient.  All the gains you get from going to LEDs
> are essentially going to be lost as heat from the regulator.

Power consumption with the LM317 will always be lower than without it; so
you're not "losing" any power.  The power dissipated in the 317 will be
matched by less power dissipated in the LEDs and ballast resistors.

Besides, we're not talking about enough power to worry about on a car.  That
whole chain of LEDs only draws 6 or 7 watts at 12v.  If you lose a watt
(0.08 amps @ 12v), who cares?

The main disadvantage (if you want to call it that) is that the LM317 has a
minimum forward voltage drop of 1.25 volts; while the PWM module should be
under 0.5 volts.  So even at "max" brightness, the LEDs will be a tiny bit
dimmer with the LM317 feeding them.  Unless of course you rig a switch to
bypass it for full brightness :)

-- Randall