i pulled an blue High Dome emitter off the star base just yesterday. I did a continuity test and it seems to be isolated from both. i havent cleaned the slug yet from the epoxy that held it on though. but i'm pretty confident of the fact.
Leon
Once upon a time the heatsinking 'slug' on the Luxeon emitters was not electrically isolated from somewhere/something dark and secret within its 'innards and the datasheet/appnotes informed of this fact - detailing that the slugs must be electrically isolated from each other .
Recently I have noticed that the slugs appear to be electrically isolated from the anode and cathode connections although I can find no Lumileds reference to this fact.
Anyone know anything about this?
Regards.
I have noticed that some Luxeons have isolated heatsinking and some do not. If the datasheet does not say anything in this area about a particular part number, assume that the manufacturer reserves the right to change that characteristic of that part number and be prepared for the worst.
- Don Klipstein ( snipped-for-privacy@misty.com)
There may be different production lines or an old batch may appear on the market, indeed.
Thomas
Posted this before, it does not seem to havge appeared.
The LED chip is glued onto the copper slug. If they change from conductive-non-conductive glue, or the chip sits slightly skew, with one corner touching the mount through the glue, it could be conductive.
The slug is electrically connected to the substrate comprising 2 inverse series zener diodes, this explains why you cannot measure with an ohm meter. See the Lumileds document RD25.pdf
Each zener may be in the range of 5v - 10v so it will not usually show a problem in low voltage applications.
Pat
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