Emitter grounding and diode question ?

[Anglepoise]

On another thread there was discussion about the Lux III emitter and its slug base continuity or lack thereof to the + and - contacts on the emitter. There seemed to be disagreement as to if the base of the emitter is connected to either contact with a diode.
I just purchased a couple of TYOJ's and with my Fluke I get no continuity and no voltage when set to Diode test.

Can someone clarify this in terms of using an emitter grounded to the heat sink that might be in continuity with the - contact.

 

[evan9162]

I know for sure that Lux I and V are like this - I have personally tested them. I have a bunch of Lux III stars, and I am unable to reproduce the results with those - but, they are still on the star boards, and the thermal adhesive may be electrically isolating them. I haven't yet removed one so I can confirm if the Lux III is the same.

For the diode test, the + test lead must be connected to the slug. Also, your meter must be able to forward bias the protection diode - how high of a biasing voltage will your meter provide? (should be spec'ed in its manual)

 

[Anglepoise]

Manual says the following under 'Forward Bias'. The meter displays the forward voltage drop ( Vf ) in volts up to 2V.

 

[evan9162]

Should be enough. I may try to separate one of my Lux IIIs from the star to see if the adhesive is isolating things.

 

[andrewwynn]

based on lumiled's datasheet.. if they follow their own rules, they are using a non-conductive adhesive on the emitter. if i think of it i'll run the diode test on an emitter with my fluke 87 and see what comes of it.

-awr

 

[gadget_lover]

I found it open with the meter, but when there was current flowing through it there was noticeable voltage drop between one of the leads and the slug.

Daniel

 

[Chop]

You guys are talking over my head about the electronics, but I can tell you that the slug on the Lux III is not neutral. The epoxy used by lumileds is non conductive and it needs to be with the Lux III.

The slug does need to be electrically isolated. I've done mods on bare aluminum lights where I forgot to isolate the slug of the Lux III emitter and the light wouldn't run. This is why anodized heat sinks are so handy.

I hope I was on point. If not, just ignore me.

 

[KevinL]

Interesting. For the Mag3X, I slapped 3 stars onto a bare Al heatsink and it ran fine. I doubt I did that great a job of isolating them, either.

 

[evan9162]

Stars generally seem to be isolated by the thermal adhesive. However, that is probably not a guarantee, hence why Lumileds warns about Lux III stars neeing to be isolated (since the slug is bonded directly to the heat sink).

 

[andrewwynn]

when i used stars i used the same thermal adhesive which is non-conductive.. oh i guess the heatsink was also anodized so it was a pretty low-risk situation. I was unaware that stars also had to be isolated.. is this a for sure thing or speculation? that kinda sucks if the stars also have to be electrically isolated. it's like they are breaking their own rules.. not using isolated method to stick the emitter on the star board.

I know i get some very interesting readings from when i'm doing a 'short' check on my lights, and pretty sure the diode check does give me a reading on luxes.. but never tried from the slug.

-awr

 

[Doug S]

I can confirm that the nature of the ESD protection on the Lux III emitters has changed from the early ones which measured around 0.6-0.7V across the ESD protection diodes. I just measured six Lux III emitters of fairly recent production from two different lots. At a test current of 1 mA [Fluke 87 on diode test function] with positive applied to the slug and negative to either terminal, a voltage in the range of 2.6 to 3.05V is seen. The slug is *not* isolated.

 

[evan9162]

[ QUOTE ]
andrewwynn said:
when i used stars i used the same thermal adhesive which is non-conductive.. oh i guess the heatsink was also anodized so it was a pretty low-risk situation. I was unaware that stars also had to be isolated.. is this a for sure thing or speculation? that kinda sucks if the stars also have to be electrically isolated. it's like they are breaking their own rules.. not using isolated method to stick the emitter on the star board.

I know i get some very interesting readings from when i'm doing a 'short' check on my lights, and pretty sure the diode check does give me a reading on luxes.. but never tried from the slug.

-awr

[/ QUOTE ]

Lumileds states that the star board should be isolated for Luxeon III and V stars. It's stated on page 2 of each data sheet, note #3 on the right side of the page.

 

[Anglepoise]

Thank you all very much. Seems like we must use a 'non electrically conducting epoxy' when using emitters.

 

[IsaacHayes]

Ok, so how does this affect us using negative connceted HS's and luxIII's? Does having the slug tied to the negative in a light cause problems? (DD, not circuit based)

Even using A-Alumina, I use it so thin and press down that a lot of metal makes contact....

 

[Doug S]

[ QUOTE ]
IsaacHayes said:
Ok, so how does this affect us using negative connceted HS's and luxIII's? Does having the slug tied to the negative in a light cause problems? (DD, not circuit based)

Even using A-Alumina, I use it so thin and press down that a lot of metal makes contact....

[/ QUOTE ]
At least for the White/blue/cyan Lux IIIs, it should cause no problem.

 

[KevinL]

/ubbthreads/images/graemlins/thanks.gif I'll sleep a lot better knowing that.

 

[andrewwynn]

re 'press down and make contact'.. you'd be surprised how few microns needed to isolate the thing electrically... there is not likely any electrical contact if you put arctic aluminum.

Good to found out about the situation with the stars.. good to know,and lucky i use non-conductive epoxy to attach the stars.

-awr