Luxeon Emitter Questions (more)

evan9162

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[ QUOTE ]
Anglepoise said:
With my Fluke set to read continuity, and one probe on the emmiter base and the other on ,first the + and then the -, I got no reading.

Doug. Is this considered isolated? I am confused.

[/ QUOTE ]

You need to use the diode test function of your DMM. Put the + on the emitter base, and the - at either of the power leads - if you have contact, it should indicate current flowing and/or (depending on your meter) show the foward voltage of the ESD diodes. If you get nothing, then things are isolated.
 

MrAl

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Hello again,

Thanks Doug S and others for the additional info.
I didnt realize that the base of the emitter was connected
to the two leads via two diodes. I guess you could say then
that the base is only 'diodically' isolated from the LED.
That's very important information!

BTW Doug your link didnt work.

Take care,
Al
 

Doug S

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[ QUOTE ]
MrAl said:
BTW Doug your link didnt work.



[/ QUOTE ]

Odd, it works for me /ubbthreads/images/graemlins/confused.gif
 

koala

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Stick your emmiter on to a stable platform before soldering. You don't want to land that 340c tip on top of the dome. That will instantly make your emmiter look sore.
 

Crux

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[ QUOTE ]
evan9162 said:

You need to use the diode test function of your DMM. Put the + on the emitter base, and the - at either of the power leads - if you have contact, it should indicate current flowing and/or (depending on your meter) show the foward voltage of the ESD diodes. If you get nothing, then things are isolated.

[/ QUOTE ]

Be sure to check the voltage your meter uses for diode testing. If the voltage is not high enough to forward bias a diode's Vf, then the diode will appear to be an open circuit.

Fluke 77 is 2.54V
Fluke 87 is 3.56V
Crappy meter at work is 1.1V /ubbthreads/images/graemlins/thumbsdown.gif Can't even use it to check polarity of red LEDs! (Vf=1.6V)

I measured 2.8V from either lead to slug on a LUX3 emitter.
 

evan9162

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Good point Crux. My meters read up to about 2V. Any more, and I don't get a measurement, but I do still get a beeping signal to indicate current flow.
 

Doug S

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[ QUOTE ]
Crux said:
I measured 2.8V from either lead to slug on a LUX3 emitter.

[/ QUOTE ]

Really?? I recall getting measurements in the 0.6-0.7V range for the whites. Could you double check this. If your measurements are correct, this would reflect a change in the ESD design. Also, what color was the emitter you measured? With the Lux Is, I do recall the cyans reading higher than the whites.
 

MrAl

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Hello again,

Doug S:
Your link works for me when im logged in, but when i
come in as guest (without logging in) it doesnt work.
Maybe this is a CPF issue someone needs to know about?
To try this, simply log out and then come back in as
guest and (maybe clear browser cache first) try again.

I'll measure my emitter (leads to base) also and post
the result too. It's only a Lux I though.


Take care,
Al
 

Anglepoise

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What does this mean in real life terms.
If the base of the emitter is grounded to the heat sink and the heat sink is the - negative path. What problems might this cause?
 

Doug S

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[ QUOTE ]
Anglepoise said:
What does this mean in real life terms.
If the base of the emitter is grounded to the heat sink and the heat sink is the - negative path. What problems might this cause?

[/ QUOTE ]
If blue/cyan/or white Lux, none if powering a single emitter or sets of paralleled emitters.
 

Doug S

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[ QUOTE ]
Doug S said:
[ QUOTE ]
Crux said:
I measured 2.8V from either lead to slug on a LUX3 emitter.

[/ QUOTE ]

Really?? I recall getting measurements in the 0.6-0.7V range for the whites. Could you double check this. If your measurements are correct, this would reflect a change in the ESD design. Also, what color was the emitter you measured? With the Lux Is, I do recall the cyans reading higher than the whites.

[/ QUOTE ]

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

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Any speculation on the nature of the change in blocking diodes? Does a blocking diode with a higher Vf indicate a more robust blocking diode, or is it even possible to deduce any information from this observation?
 

Doug S

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[ QUOTE ]
evan9162 said:
Any speculation on the nature of the change in blocking diodes? Does a blocking diode with a higher Vf indicate a more robust blocking diode, or is it even possible to deduce any information from this observation?

[/ QUOTE ]
I cannot draw any conclusions. A new question comes to mind though. If anyone has a recent production Lux I emitter handy, I would be curious to see how they measure. That would add some fuel to the speculation about whether or not there remains a difference in the structure of Lux Is vs Lux IIIs. Some have speculated that Lux Is are now Lux IIIs that didn't make the grade. I personally don't have any position on this other than "I don't know".
 

Doug S

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Darin, one other thing. Figure 15 in AB25 [Luxeon Reliability] shows the internal structure of the Lux I and III protection. It shows back to back zeners with anodes on the slug. As drawn, you should see the 0.7V slug to terminal that we have previously seen. The rev of AB25 that I am looking at is dated 02/04. Assuming that the AB25 was correct when published [which is not a good bet with Lumileds], the change to the Lux III structure would be more recent. I'm still curious how a recent production Lux I would measure.
 

MrAl

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Hi Doug S,

I could measure mine too if that would help. I just
got it.

BTW, i didnt realize you were from Georgia. I had a friend
from Georgia long long time ago (Atlanta). We went to
school together in Massachusetts.

Take care,
Al
 

Doug S

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[ QUOTE ]
MrAl said:
Hi Doug S,

I could measure mine too if that would help. I just
got it.

BTW, i didnt realize you were from Georgia. I had a friend
from Georgia long long time ago (Atlanta). We went to
school together in Massachusetts.

Take care,
Al

[/ QUOTE ]
Al,

Since you have a Lux I, please do.
I just moved to Georgia a couple of weeks ago. I last lived in Georgia [Atlanta] 1970-75 when I was attending Georgia Tech.
 
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