Luxeon slug should be neutral?

Rebus · Apr 30, 2003

I was just reading the spec sheet on the
LS and it said that the slug on the bottom should be
isolated from both the negative and positive
side of the circuit. I am building a mod
in which this will be very hard to do.
I was going to epoxy the LS to the heatsink
with thermal transfer compound under the slug.
It is nearly imposible to isolate the heatsink
from the barrell of the light (neg side).

Should I try to insulate it or is this something
I need not worry about?

-Rebus

LED_ASAP · Apr 30, 2003

You will need to keep the slug "floating", as indicated on the data sheet. Once I test-run a LS-emiter with a lithium button-cell, and found if the slug touched either (+) or (-) the emiter would not light---meaning it's draining too much current that the button cell could not keep the voltage. You can find grey insulating pads from most computer-repair shops or if you have old PC power supplies around, you can find one under the power transistor.

robk · Apr 30, 2003

I used Arctic Alumina Epoxy to stick an emitter on a grounded heat sink without any problems.
1. I believe the epoxy is thermally conductive, but not electrically conductive
2. Even if you ground the slug, I believe you only disable one of the static zener protective diodes on the die (but if grounded, it's not needed)
3. I think it's only an issue if you mount multiple emitters on a common ground.
Please correct me if I'm wrong. It's worked for me, but the data sheets on the luxeons are vague on this matter.
Rob

tvodrd · Apr 30, 2003

Rebus,

What color LS? With the whites (several 1Ws and one 5W) I have done exactly as you describe- slug epoxied to neg side, and haven't had a problem yet. I have read here that the colored ones are a different story. (If you're really picky, you can lap the slug first /ubbthreads/images/graemlins/grin.gif .)

Larry