SparkFun Forums

[rappa]

yep, the problem was the lack of common ground.

I'm thinking of using a LM317 as a constant current source http://www.instructables.com/id/Super-s ... /?ALLSTEPS

Does anyone know if this circuit is compatible with PWM, using a MOSFET?

[bigglez]

I'm thinking of using a LM317 as a constant current source. Does anyone know if this circuit is compatible with PWM, using a MOSFET?

It is a constant current SOURCE (not sink),
so current flows to ground from the output. Your LED
Cluster IIRC is common anode, so this will do nothing
for you. What you might have considered was a
constant current SINK, and used one each for RGB.

If you have a common cathode LED cluster this circuit
can power one of the LEDs (use three for all LEDs).

[rappa]

I'm thinking of using a LM317 as a constant current source. Does anyone know if this circuit is compatible with PWM, using a MOSFET?

It is a constant current SOURCE (not sink),
so current flows to ground from the output. Your LED
Cluster IIRC is common anode, so this will do nothing
for you. What you might have considered was a
constant current SINK, and used one each for RGB.

If you have a common cathode LED cluster this circuit
can power one of the LEDs (use three for all LEDs).

There are 3 anodes and 3 cathodes so I think it should be ok. Here's a picture of the led http://www.sure-electronics.net/DC,IC%2 ... L007-2.jpg

[bigglez]

There are 3 anodes and 3 cathodes so I think it should be ok. Here's a picture of the led

Yes, that scheme will work to light them up. You'll
need three identical regulators. There is no provision
to turn then on or off (or PWM them for intensity
control).