# Isolation of Luxeon slugs



## evan9162 (Sep 4, 2005)

There has been a lot of question about the fact that the slug on Luxeon emitters is not electrically neutral. 

It is well known that the slug for Red/Orange/Amber luxeons is tied directly to positive. Those that were not aware of this fact, or were not able to sufficiently isolate the slug of these luxeons from the often ground-bodied flashlights serving as hosts were given a grim reminder of this fact when their luxeon lived a very short life. Allowing the slug of one of those types of luxeons to contact ground while in operation causes a short directly across the bond wire of the positive lead, ultimatley fusing the bond wire open. The luxeon could still be used in this case, since the bond wire merely connected the positive lead to the slug - but to the unknowing user, the LED appears to be toast.

It was long thought that the slug of white/green/blue Luxeons was tied to negative. This, is in fact, not true. The slug of these models of luxeon are tied to the positive and negative leads through zener diodes that serve as ESD protection. You can verify this yourself: using the diode test function on your DMM, connect the positive probe to the slug, and the negative probe to either of the power leads. Your DMM should forward bias these ESD diodes, and read something like 0.6-0.7V as the diode's Vf.

Thus, the circuit diagram for a white/blue/green Luxeon (heretofore refered to simply as Luxeon) looks like this:







Now, based on my testing today, and the above circuit configuration, I'd say that it is "safe" to tie the slug of a luxeon to ground in the single luxeon case. In addition, I'd deem it "safe" to tie multiple luxeon slugs together when in a parallel configuration, provided that all of the slugs and all of the grounds are tied to a common point.
Now, I use the term "safe" loosely, because, if it were myself, I'd still prefer to keep the luxeon slugs isolated from each other, and the heat sink, just in case.

However, it is absolutely imperative that *all slugs be completely isolated* both from each other, and from ground, when running multiple luxeons in series.

Below, is a diagram, based on the above schematic including ESD diodes, of 3 Luxeons in series:







I did some measurements on a set of 3 bare Luxeon emitters in series, at about 28mA test current. I then simulated the slugs being electrically tied together by pushing them against a strip of aluminium bar stock. This was driven with an LM317 in current mode, with a 47 ohm resistor, yielding 27.6mA of test current. The emitters could be run bare at this test current level, without any heatsinking.

Here are the test voltage results of running the 3 emitters in series with the slugs completely isolated:






The voltages across the ESD diodes should be fairly accurate - bypassing the ESD diode on the - terminal with the 200uA current scale on my DMM, I measured several microamps flowing - so in normal operation there is several uA of current flowing from the '+' terminal, through the first ESD diode, through the slug, and through the second ESD diode, to the '-' terminal. This forward biases the '-' terminal ESD diode, so there is usually ~0.6V between the slug and '-' terminal when the slug is isolated.

Now, I first caught wind that these were zener ESD diodes from some Lumileds documentation - though not from the datasheet its self. IMO, the first diagram I showed is really needed in the Luxeon datasheets - it allows an engineer to truly understand the electrical relationship of the slug to the two power terminals. Anyways, being that these are zener diodes, that means there is a zener voltage where the diode is reverse biased, and current begins to flow rapidly. The zener volage of the positive terminal ESD diode is at the heart of why luxeons in series must have their slugs electrically isolated from each other and ground.

In my testing, based on the above diagram, I experienced issues when the slugs of Lux #1 and Lux #3 were in electrical contact. Connecting the slugs of Lux #2 and #3 together had no effect, as was the case with connecting Lux #1 to #2.

When the "failure" mode was introduced, all 3 luxeons went fairly dim. The connection of the Lux #2 slug had no effect on the behavior when #1 and #3 were connected.

Below, is the diagram that illustrates the failure mode:






The only difference that connecting Lux #2's slug makes is on the voltages of the ESD diodes for Lux #2, so the rest of the information in above diagram is correct regardless of the connection of Lux #2's slug.

From this diagram, we can see that, in the failure mode, the majority of the current (path in red) is being dumped through the now reverse-biased (zener-biased) '+' ESD diode of Lux #1, into the slug, to the slug of Lux #3, and through the forward biased '-' ESD diode of Lux #3. A small amount of current still flows through the 3 series luxeons, but at 1.2mA, they are quite dim.

Another important thing to note: the total volage of the series string has dropped from 8.49V to 7.58V - almost 1V drop. My luxeons survived without damage because I was using a current source - but those that would be using a resistored setup, or even direct drive for 3 series luxeons, would see the current increase dramatically.

I do not know how much continuous current the ESD diodes on luxeons are designed to handle. I would imagine that they aren't designed to be carrying continuous current of more than a few 10s of mA for very long. I have no idea if carrying hundreds of mA to an amp of current would destroy the ESD diodes or not. If they failed to an open circuit, then the luxeon would operate as normal, but without ESD protection. But if they failed as a short, then they would either pass all the current through the slug into the other ESD diode, or (without a current limited power source) possibly pass so much current that the bond wires fuse. In the former case, the luxeon still passes current, but with a Vf of approx 0.7V, no current flows through the LED portion. In the latter, the luxeon passes no current. In either case, the luxeon is rendered essentially useless.

Now, from what I observed, it would appear that you only need to ensure slug isolation if running 3 or more luxeons in series - but that's not so. I was only running these at ~30mA. If running them at higher currents, the combined Vf of just two in series would easily exceed the ~7.5V voltage required to reverse bias the '+' ESD diode of one Luxeon, and forward bias the '-' ESD diode of the second. At this point, some current would be passing through the ESD diodes and slugs of the luxeons, and not through the LED junctions them selves - proving the extra current to be completely wasteful. Thus, even two luxeons in series can experience the same failure.


So that covers the situation where the slugs of series luxeons are tied together, but not connected to ground. As a last test, I connected the aluminium bar to ground, and repeated the test.

With the slugs connected and tied to ground, things are a little simpler. Once the slug of Lux #1 comes in contact with ground, then all 3 luxeons in the string go out. There is no effect if either or both of the other two slugs contact ground.

Below illustrates what's happening when the slug of Lux #1 contacts ground:






Again, the '+' ESD diode of Lux #1 is reverse (zener) biased, and passes pretty much all of the current (in red) directly to ground, bypassing the LEDs. I've labled the current passing through the Luxeons themselves as ~0mA (approximately zero) - because, while the luxeons did not light up at all, I did measure distinct voltage drops across the terminals of each luxeon - telling me that a tiny amount of current is actually flowing, but not enought to produce any light. I just ran out and measured it - it's about 18uA of current.

So in this case, there isn't any indication of what's going on - the string simply doesn't light up. And for those not using a current regulator, it's worse - the voltage has dropped down to 6.75V - almost 2V lower than if the string were functional - a resistored or DD setup will dump a lot of current into the poor ESD diode. But not all current regulators will handle this scenario. Current regulators that rely on a sense resistor being between the '-' terminal of the LED and ground will also have issues. Since that sense resistor is being bypassed, the regulator will run wide open, dumping as much current into the LEDs as possible - and all of it will go through the single ESD diode - likely leading to its destruction, and /or other damage to the Luxeon.

Again, as with the non-grounded example, I did not experience issues with connecting the slug of Lux #2 to ground, but given a setup that will deliver higher current, a series string of 2 will also experience this failure if the slug of the "first" (connected closest to "+" of the power source) luxeon touches ground.


So - after all of that - what does all of this amount to? Simple - when running luxeons in series, you absolutely *must* isolate all slugs from each other and ground. Failure to do so could result in one of the two failure modes described above where a) the luxeons are dim (possibly flickering), or b) the luxeons fail to light up at all. Contunuous high current operation in one of these failure modes could lead to damage of one or more of the luxeons in the series string.

When connecting luxeons in parallel, it is still a very good idea to isolate the slugs of all emitters from each other and ground - in fact, I would even stronly suggest it just for a single luxeon, as it is the only way to be absolutely safe.

One more note - it is best to treat Luxeon III and V stars as bare emitters with respect to isolation. The star construction and thermal bonding that is applied for these stars is such that it cannot be guaranteed that the slug will be isolated from the metal heat sink star. While it may appear that your stars are isolated, best practices would dictate that you isolate III and V stars from each other as well.


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## evan9162 (Sep 4, 2005)

Some more info - 

I checked the zener voltage of ESD diodes on my 3 luxeon V lights. The zener voltage is around 7.3V.

Given that the Vf of Luxeon V LEDs is quite close to that figure, tells me that even single luxeon V LEDs should have their slugs isolated from ground. For those who overdrive their luxeon Vs, if the slug is not isolated from ground, then when the Vf of the Luxeon is above 7.3V, then significant amounts of current will begin to pass through the '+' ESD diode to ground. The current that goes through that ESD diode is completely wasted and is simply dissipated as heat.

So, I would say that isolating the slug of a Luxeon V is an absolute *must* in all scenarios.


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## wquiles (Sep 4, 2005)

evan,

This is awesome information that will come in very handy. Thanks much!

will


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## Burnt_Retinas (Sep 5, 2005)

:twothumbs: Just the sort of info we need to plan for the future with the K2's.

I am surprised the clamping voltage begins at such low voltage (say ~5V?) for 2k ESD, but it looks like that's the way it is in the practical world with the K2.

Thanks for the effort researching real-world use of this beast.

Chris


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## PeterB (Sep 5, 2005)

Thanks! Great Info!


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## andrewwynn (Sep 5, 2005)

great review... i think you answered one of my questions about a 'bug' i've had in a light or two... i'd have 4 series lights and 'sometimes' i would have 3 go out and one lit really really dimly... the driver kept running the one emitter lit did not seem to care or complain.. it was very bizarre.. i'm not sure which emitter slug would have had to be grounded and to what to have it happen but it would seem that's what did happen. 

-awr


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## Anglepoise (Sep 5, 2005)

Great info. Thank you very much.
I am just about to start a task light mod using 3 Lux III's and this info is invaluable.


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## McGizmo (Sep 5, 2005)

Thanks for the enlightenment and explainations!! :thumbsup:

I suspect the ESD protection is worth the price of the slug isolation! I have lost other LED's in the field due to no protection and that can be a PITA.


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## evan9162 (Sep 5, 2005)

andrewwynn said:


> great review... i think you answered one of my questions about a 'bug' i've had in a light or two... i'd have 4 series lights and 'sometimes' i would have 3 go out and one lit really really dimly... the driver kept running the one emitter lit did not seem to care or complain.. it was very bizarre.. i'm not sure which emitter slug would have had to be grounded and to what to have it happen but it would seem that's what did happen.
> 
> -awr



I haven't had the courage to do this test with higher currents - but I'd bet it's something like a combination of the first and second slugs shorting to ground.


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## HarryN (Sep 6, 2005)

Thanks Evan, that explains a lot of questions I have had.


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## HarryN (Sep 7, 2005)

Hi Evan - Now I have another question.

I would like to set up a light with a a Lux III, +, -, and slug grounded. The slight difference from your posted circuit is that there is a reverse battery protection diode (Vf around 0.2V) between the - and ground.

There actually is a good reason for doing it this way, which will become obvious soon.

Do you perceive any issues ? Thanks


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## evan9162 (Sep 7, 2005)

Harry,

Putting the diode on the - terminal probably isn't the best idea with the slug grounded - if you do so, and the batteries are put in backwards, then it will forward bias the ESD diode on the '+' terminal. The battery protection diode would work best on the + terminal ... then if the batteries are inserted backwards, none of the ESD diodes will be forward biased.


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## andrewwynn (Sep 8, 2005)

Hey harry thanks for the idea of putting in reverse protection.. methinks that the fatman driver is not too happy about reverse voltage i might put that in my BAM! design.. though i think there is a hardware interlock on the MAG light since the positive post is a spring that is kind of recessed. i'll have to look into this.

-awr


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## wquiles (Sep 8, 2005)

Evan,

Would you say that in most cases of multiple (3 or 4 Lux's) like those using the "Perfect Tri Sink" of "Perfect Four Sink" folks are basically getting "lucky" since the AA epoxy has in most cases isolated the slug from the cooper/aluminum heat sink which is most always contacting the body of the M*G light (and therefore ground)?

This makes me wonder what is the correct way of installing 3 and 4 emiters/stars in these awesome heatsinks to "guarante" no problems 

Will


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## evan9162 (Sep 8, 2005)

If the luxeons are wired in parallel, then they're much safer than if they're wired in series. If they are in series, then I'd say they're getting lucky.

I'd say the installation methods are probably okay, but that isolation should be checked with a multimeter before the epoxy (AA) sets up. That's what I've done with my R/O mods.


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## cy (Sep 20, 2005)

evan, no question slug needs to be isolated from common. 

what is the best way to achieve this? 

thin layer of AA expoxy, let set hard to form insulation layer. then AA expoxy again (or AA grease & screw) for final connection. 

thanks,


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## 3rd_shift (Sep 21, 2005)

Interestingly, my 4x3 watt RO Luxeon 4c magmod with 3 18650's driving it all in series is still doing well.
I will be removing the thermal grease from under the stars and replacing it with thermal epoxy anyways to improve it's reliability.

I have 4 more unused Luxeon3 RO stars and they all light up nicely from the metal star being touched by the (+) tip of a cr123 and a (-) wire touching a negative pad on the star.


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## NewBie (Sep 21, 2005)

McGizmo said:


> Thanks for the enlightenment and explainations!! :thumbsup:
> 
> I suspect the ESD protection is worth the price of the slug isolation! I have lost other LED's in the field due to no protection and that can be a PITA.




Just think of them as ESD condoms for LEDs.


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## Justintoxicated (Sep 21, 2005)

NewBie said:


> Just think of them as ESD condoms for LEDs.




I had a Red Star go out on me and everythign on the LED worked perfect.

I'm guessing that if I would have re-soldered the wire to the Positive Base of the Star it would have turned back on...

Well if anyone wants it they can have some fun at the dump searching for it 

So here is a Queston...

This gives me some great ideas for modding a Mini Mag with a RED led...I guess you could just put the batteries in backwards and make life alot easier on yourself!


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## andrewwynn (Sep 21, 2005)

i like the idea of pre-coating with AA epoxy! i think i first saw that suggestion from Mr. Bulk but seeing it again hammers it home.. i had an emitter or two wig out on me by shorting 'just ever so slightly' through a heatsink it is a miracle it was only one i still dont' know how only one emitter lit up or exactly why.. forutunately i did figure out that it was an open grounnd coupled with an coincidental grounding of the heatsink.. there was enough power getting through the slug through the AA epoxy that i think that on at least one of my upcoming designs i will be using the exact method desribed to isolate the luxeons. (AA epoxy.. let dry.. and use AA paste or AS paste on top of that for a removable solution...) i was going to just use AA paste but after reading all this and having a weird 'semiconducting short' happen i'll take the pass on that!


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## kubolaw (Sep 21, 2005)

But doesn't a layer of AA severly diminish heat transfer properties? All my experience with CPU heatsink mounting tells me that you want as little AA as possible - just enough to fill in the surface irregularities that come from mating surfaces that are not perfectly flat. That's why people lap their CPU heatsinks, and I think even the AA (paste) instructions explicitly state that you should use a very thin layer of AA.

Probably not an issue for smaller lights, but for something like the BAM, I'd think you'd want/need the best thermal path possible.

John


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## andrewwynn (Sep 21, 2005)

i used to worry about the same thing.. the thing is.. a CPU you have to transfer about 12-15x the heat from it.. AA is pretty darn conductive.. and the beauty of using the two-layer method is you can control that first layer (you can seeee it).. and the second layer can be microns thick.

BAM actually i think i will solve that case by anodizing.. anybody know what the reliability of the non-conductiveness of anodizing is? 

I have had ok luck so far when i really spread the AA epoxy thing by sliding the emitter around in circles to spread it very thin, but once or twice i've had an imprefect insulation situation and more than once i've had a hot emitter pop free from the heatsink and self desctruct (rather quickly i might add). 

after having a couple examples of emittesr not having a strong attach and a couple where apparently the aa was too thin (semi-short).. i am liking the idea of the two-layer model. 

-awr


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## tvodrd (Sep 21, 2005)

The heat flow equation is a linear function of area, thickness, deltaT, and the thermal conductivity of the heatsink compound. A .001" (one thousandth of an inch) thickness of heatsink compound will only flow 1/10th of a layer .0001" thick under otherwise equal conditions! I should add that the thermal conductivity of *good* heatsink compounds is a small fraction of that for metals! IMO, the "hot setup" is to lap the slug and heatsink flat when possible and press the LS down as hard as you can. A TypeII anodized sink is the _best_ solution for a red/RO LED with a neg flashlight ground. Fortunately, evan9162 explains how to check if you have pressed down a little too hard.

Larry


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## andrewwynn (Sep 22, 2005)

there is somethig missing from your equation... the thickness (10x in your example) does not allow 1/10th the heat.. the only difference is that the heat gradient runs farther on that linear direction which is very short in either case.. that simply means there is a larger difference in temprature which will be 10x.. but if it's thin enough to start with that means it could be a 0.01F temp gradient in the 'good' example and 0.1F temp gradient (ten times the difference).. thanks for the tip on the anodizing.. that will likely work very well for MM and BAM designs..so.. for example if something has a conductivity of 400F/inch/W and you are putting 4W through that heat slug.. means that you have 4W * 400F * .001 = 1.6F heat gradient.. and with 0.0001 thickness.. you get 1/10th the gradient or 0.16F.. (virtually nothing)... 

now.. move that up to an 80W overclocked CPU.... that makes the numbers 20x and that means.. 32F gradient on the 0.001 model and 3.2F gradient on the 0.0001 model.. 

So.. after realizing this situation.. i've come to understand that 'the point is moot' you could probably use elmer's glue without a serious performance degradation.. 

example.. there is at least a 13C/W varation from the junction temperature to the slug temprature.. and even though i pulled the values out of my butt for the example.. the concept directly applies... so at 4W you have 93F of temp gradient from the junction to the slug.. consider than.. how insignificant will the temp. gradient be across the film of the slug adhesive is in the big picture.

-awr


-awr


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## balazer (Sep 22, 2005)

Can anyone suggest a place to buy a small aluminum plate or disc, perhaps anodized? I'd like to mount some Cree LEDs on a flat metal heat sink, 4 - 5 cm round, and 0.5 - 1 cm thick, or however thick you guys think is good enough for 6 LEDs. Is aluminum something I can cut myself, or am I better off to buy it pre-cut?

In case you haven't seen the Cree LEDs, they have a flat bottom with three contacts - the two electrical contacts and the heat path. They're meant to be surface mount reflow soldered, but I want to put them on a big flat heat sink instead. Of course I want to maximize thermal conductivity between the heat sink and the LEDs' thermal paths, but I need to electrically isolate the electrical contacts. Would I be just as well of to put a thin layer of Arctic Alumina adhesive on the underside of the electrical contacts to isolate them, instead of getting an anodized aluminum plate?


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## chimo (Sep 22, 2005)

Balazer, note that the electrical contacts are duplicated on the top side of the package. I have actually "dremmeled" them off the bottom on one mod I did.

Paul


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## balazer (Sep 22, 2005)

Good idea, Paul. Thanks.

I'm still wondering where I can buy the heat sink.


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## andrewwynn (Sep 23, 2005)

the size you describe might be very similar to the size of b2eze's mag heatsink... are you putting it in a mag? that HS screws right in,.. it has a hole in the middle for wireing... it's a 'beaut'. 

-awr


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## balazer (Sep 23, 2005)

Yes, I'll be putting this in a Mag - but a 2C, not D. So a simple aluminum disc in the bezel will be perfect. The heat sink will sit further up in the bezel atop the ledge, as opposed to further down in the bezel like how most Mag D mods would be. A 2C's bezel is narrower at the base compared to a D.


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## Tritium (Sep 23, 2005)

balazer said:


> Can anyone suggest a place to buy a small aluminum plate or disc, perhaps anodized? I'd like to mount some Cree LEDs on a flat metal heat sink, 4 - 5 cm round, and 0.5 - 1 cm thick, or however thick you guys think is good enough for 6 LEDs. Is aluminum something I can cut myself, or am I better off to buy it pre-cut?


 When you buy Crees just ask for them to be mounted on heat sinks. There is no extra charge from ETG for doing this.

Thurmond


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## balazer (Sep 23, 2005)

Those heat sinks are too large to allow me to pack the LEDs as tightly as I want to.


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## NewBie (Oct 9, 2005)

balazer said:


> Can anyone suggest a place to buy a small aluminum plate or disc, perhaps anodized? I'd like to mount some Cree LEDs on a flat metal heat sink, 4 - 5 cm round, and 0.5 - 1 cm thick, or however thick you guys think is good enough for 6 LEDs. Is aluminum something I can cut myself, or am I better off to buy it pre-cut?
> 
> In case you haven't seen the Cree LEDs, they have a flat bottom with three contacts - the two electrical contacts and the heat path. They're meant to be surface mount reflow soldered, but I want to put them on a big flat heat sink instead. Of course I want to maximize thermal conductivity between the heat sink and the LEDs' thermal paths, but I need to electrically isolate the electrical contacts. Would I be just as well of to put a thin layer of Arctic Alumina adhesive on the underside of the electrical contacts to isolate them, instead of getting an anodized aluminum plate?




When I was prototyping, and also with my 192W array of the CREEs, this is an example of what I did. The tape used is a Kapton (polyimide), such as 3M 5413 from Mouser. Notice the CREE is directly soldered to the copper plate.

5413 tape has a polyimide Kapton® Type (H)
backing that is flame resistant, radiation resistant
and chemical resistant. The polyimide Kapton®
backing does not soften at elevated temperature,
providing an excellent release surface when used
at temperatures above 204°C.

517-5413-1/2 
517-5413-3/4


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## OddOne (Oct 11, 2005)

balazer said:


> Can anyone suggest a place to buy a small aluminum plate or disc, perhaps anodized? I'd like to mount some Cree LEDs on a flat metal heat sink, 4 - 5 cm round, and 0.5 - 1 cm thick, or however thick you guys think is good enough for 6 LEDs. Is aluminum something I can cut myself, or am I better off to buy it pre-cut?
> 
> In case you haven't seen the Cree LEDs, they have a flat bottom with three contacts - the two electrical contacts and the heat path. They're meant to be surface mount reflow soldered, but I want to put them on a big flat heat sink instead. Of course I want to maximize thermal conductivity between the heat sink and the LEDs' thermal paths, but I need to electrically isolate the electrical contacts. Would I be just as well of to put a thin layer of Arctic Alumina adhesive on the underside of the electrical contacts to isolate them, instead of getting an anodized aluminum plate?




My solution...






I turned a post out of the aluminum and cut out a matching PC board plate, etched the board as necessary, and used an engraving bit in a B&D RTX rototool to grind down two flats on the post so that the electrical contacts cleared the aluminum. Some Artic Alumina epoxy secures the LED to the post and solder secures the contacts to the circuit board. I finished up with a light lapping job onto the base of the aluminum so that when I bond it to whatever it'll bond nice and flat.

Poof, Lux Star clone. 

oO


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## Pinter (Oct 12, 2005)

In this document there is also some useful info on the internal package structure of luxeons. See page 10-11.
http://www.luxeon.com/pdfs/RD25.PDF


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## HarryN (Oct 12, 2005)

Hi Pinter

I re-read the related parts of that AB again, and interestingly, there is a specific section from LL about the imporance of complete slug isolation. (not that I always do it).

If I read it correctly, the diode in the part is designed for occasional use, not constant use, implying that if the slug were grounded on a Lux I or III, it would in fact cause long term reliability problems. 

I wonder how real that problem is.


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## cy (Mar 15, 2006)

bump..


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## greenLED (Mar 20, 2006)

evan9162 said:


> ...even single luxeon V LEDs should have their slugs isolated from ground. For those who overdrive their luxeon Vs, if the slug is not isolated from ground, then when the Vf of the Luxeon is above 7.3V, then significant amounts of current will begin to pass through the '+' ESD diode to ground. The current that goes through that ESD diode is completely wasted and is simply dissipated as heat.



Had been wondering about that.

Would this be a non issue if the total voltage from the batteries was under 7.3V (and a converter used to step up the voltage)? I'm electronix-impaired, please "beer"  with me.


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## the_beast (Mar 20, 2006)

Also would this be an issue for the new batch of s-bin LuxVs that have arrived? (Vf around 6 volts).

I have some electronics knowledge but the diode talk in this thread has me confused :huh2: 




greenLED said:


> Had been wondering about that.
> 
> Would this be a non issue if the total voltage from the batteries was under 7.3V (and a converter used to step up the voltage)? I'm electronix-impaired, please "beer"  with me.


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## evan9162 (Mar 20, 2006)

greenLED said:


> Had been wondering about that.
> 
> Would this be a non issue if the total voltage from the batteries was under 7.3V (and a converter used to step up the voltage)? I'm electronix-impaired, please "beer"  with me.




It really doesn't matter how or what the power source is, if the slug is grounded, and the voltage of one of the power leads (the positive, in this case) relative to the slug exceeds 7.3V, then you could have issues.


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## evan9162 (Mar 20, 2006)

the_beast said:


> Also would this be an issue for the new batch of s-bin LuxVs that have arrived? (Vf around 6 volts).
> 
> I have some electronics knowledge but the diode talk in this thread has me confused :huh2:



I don't think I saw any relationship between Vf and the zener voltage of the ESD diodes. That is, while the Vf of a luxeon may vary among individual samples, the Vz of the ESD diodes should be the same across all of them.


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## greenLED (Mar 21, 2006)

evan9162 said:


> It really doesn't matter how or what the power source is, if the slug is grounded, and the voltage of one of the power leads (the positive, in this case) relative to the slug exceeds 7.3V, then you could have issues.


So, having a converter thrown in the mix won't prevent this from hapenning?


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## the_beast (Mar 21, 2006)

This is getting kinda confusing just having mine and GreenLEDs questions going on at the same time now  .

So if the Vf is lower than Vz (ie a low forward voltage LuxV, S or T bin), then slug isolation is not an issue? I assume the power source voltage would be unimportant in this case, as it's voltage must be below 7.3v if the LED Vf is below this. I hope this is true as it makes the design of my LuxV heatsink much easier (and hence cheaper) whilst keeping the heatsinking as good as possible for my new project.

Are there any other reasons to keep the slug isolated? I will only be running a single LuxV. Will I be leaving myself open to failure due to some other methods? I don't know if this is related at all, but is the led more easily damaged by static etc if the slug is not isolated?

Thanks for the help.


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## evan9162 (Mar 21, 2006)

greenLED said:


> So, having a converter thrown in the mix won't prevent this from hapenning?




Nope.


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## evan9162 (Mar 21, 2006)

the_beast said:


> So if the Vf is lower than Vz (ie a low forward voltage LuxV, S or T bin), then slug isolation is not an issue?



As long as you're running the luxeon at spec. If you overdrive, and overdrive enough that the Vf approaches Vz, then you could have problems.


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## greenLED (Mar 21, 2006)

:thanks: very much, evan! It's clear now. Thanks for your patience.


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## cmacclel (Mar 21, 2006)

I have a few Cyan LEDS on their way and was wondering how they apply to the LED Isolation rule?


Mac


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## evan9162 (Mar 21, 2006)

All white/blue/green/cyan luxeons must follow the isolation rule with regards to the ESD protection diodes.

All red/orange/amber luxeons must follow the isolation rule period, as the slug is directly connected to the + lead. The connection is through a thin gold bond wire which does a very good job as acting like a fuse at high current. Failure to properly isolate one of these Luxeons will result in high current flowing from the positive lead, through the bond wire, and out the slug, fusing the positive bond wire open and leading it to be disconnected. The luxeon could still be powered by applying the + connection to the slug, but it is not the suggested method of powering it. If there is no way to apply power to the slug, then the luxeon is rendered *dead* and useless.


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## greenLED (Mar 21, 2006)

evan9162 said:


> All red/orange/amber luxeons must follow the isolation rule period, as the slug is directly connected to the + lead. ... The luxeon could still be powered by applying the + connection to the slug, but it is not the suggested method of powering it. If there is no way to apply power to the slug, then the luxeon is rendered *dead* and useless.


 Sweet! So "dead" Luxes may be revived (with a bit of effort, of course).


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## MillerMods (Mar 21, 2006)

Well, I've never tried one of the red Luxes, and now I won't need to waste my time. Thanks for your research and time Evan. I had recieved some requests for red Luxes in my ARC mods. I guess that won't be possible unless I find a different solution for heat sinking the lux to the case.


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## evan9162 (Mar 27, 2007)

Everyone,

Looks like lumileds has finally decided to let everyone else in on this little "secret".

Check out this document:
http://www.luxeon.com/pdfs/AB29.pdf (K2 Assembly guide)

Then go to page 7

Those diagrams look kinda familiar, don't they???


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## easilyled (Mar 27, 2007)

:wow: 
I take it they didn't ask your permission?


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## evan9162 (Mar 27, 2007)

I've never heard from them.

AB29 hasn't been indexed yet by google (neither has AB32, the assembly guide for Rebels), leading me to believe that it's a new document (just like the Rebel assembly guide).


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## rscanady (Mar 27, 2007)

Since this is common schematics, I dont think that for something of this nature (ie Luxeon design, and not a complex circuit) that one would need anothers permission to draw out a schematic design. I do this all the time in school for Eng. Labs. Anyone in this field who was putting the design on paper or in Spice would end up with the same design. 


Ryan


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## evan9162 (Mar 27, 2007)

No, but it's very interesting that they used the exact same configuration (3 in series, where the phenomenon could happen with 2 or 4), and coloring scheme (red indicating current flow, with the current carrying circuit components completely colored in) as my diagrams. It's not just the similar diagram, the identical color scheme makes it more "interesting"

Plus, their explanation first shows a single device, then 3 connected in series operating normally, then 3 in series operating with a slug isolation problem. Where have we seen that before?

Besides, their document does a much worse job than my diagrams/description of characterizing a slug isolation problem. Their document just says "hey this can happen", my explanation says "this is what's happening, here's why, and here are the characteristics of luxeons in this current state". They do not mention the slug-connected-to ground scenario. They also do not mention the possibility of damage to the parts, where I specifically call out that possibilty. 

It seems like a half-assed job of pointing out the slug isolation problem.


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## rscanady (Mar 27, 2007)

I see your point


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## evan9162 (Mar 27, 2007)

It's not really that bothersome, in fact, it's actually kinda flattering if they got their ideas from here.

Should I contact them just to see what they'll say about this?


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## hank (Mar 27, 2007)

Chuckle. You probably already _have_ contacted them.

Hello? Luxeon? Come in please.


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## PhotonFanatic (Mar 27, 2007)

evan9162 said:


> It's not really that bothersome, in fact, it's actually kinda flattering if they got their ideas from here.
> 
> Should I contact them just to see what they'll say about this?


While I don't know if they got their diagramatic scheme from here, I do know that they get a lot of chuckles from CPF. Occasionally, I'll get an e-mail about certain threads that leave them laughing in the aisles. No, they aren't being malicious in their laughter, just in awe of what some of the CPFers will go to for extremes.


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## evan9162 (Mar 27, 2007)

Probably amazed that people could be so obsessive over their products.


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## ViReN (Mar 28, 2007)

> AB29 hasn't been indexed yet by google (neither has AB32, the assembly guide for Rebels), leading me to believe that it's a new document (just like the Rebel assembly guide).



Yup it's recently created.... here is the XMP footprint of that PDF


> <?xpacket begin='﻿' id='W5M0MpCehiHzreSzNTczkc9d'?><x:xmpmeta xmlns:x='adobe:ns:meta/' x:xmptk='XMP toolkit 3.0.1-30, framework 1.6'>
> <rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#' xmlns:iX='http://ns.adobe.com/iX/1.0/'>
> 
> <rdfescription rdf:about=''
> ...


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