Production CREE XR-E Testing

[IsaacHayes]

Boost. used for:
battery voltage is lower than needed for the LED to pull your desired current. Vin < Vf.

Buck: Battery voltage is higher than led Vf.

boost-buck: used when you have multiple battery voltages (primary and recharable) or the battery voltage is very close to the Vf of the led. Like starting it it's too high, then partially drained it's too low. The circuit keeps it at the right level to the led the whole time.

FluPIC is used with a higher voltage in than Vf, and IIRC it's not as efficeint as buck (which converts extra voltage into current, thus drawing less from the batteries than the led actually sees.). I believe it's called LDO which is kind of like a varible resitor if I'm correct in that it just turns extra voltage into heat inside itself.

 

[Calina]

What does LDO stand for? Same for IIRC ?

Is there a post somewhere, or a sticky, or something, that translates all those abreviations acronyms etc into proper english?

Is Flupic just a name or is it also an abreviation, if so what does it mean?

Thanks.

 

[IsaacHayes]

IIRC= if i recall correctly. LDO i think is limited drop out. flupic is a name of a driver.

 

[Calina]

Wow, that was fast!

Thank you very much.

 

[Pinter]

[Parallel operation]
There will be serious issues when operating several XR-E in parallel.
Vf vs I curve is so flat that even a small difference in Vf results in big difference in current.

I do not know how consistent the Vf-I curve is within a production batch, but even 0,1V difference yields 100-150mA difference in current below 700mA.

 

[glire]

What does LDO stand for? Same for IIRC ?

Is there a post somewhere, or a sticky, or something, that translates all those abreviations acronyms etc into proper english?

Is Flupic just a name or is it also an abreviation, if so what does it mean?

Thanks.

http://www.cygwin.com/acronyms/

 

[chimo]

I did a *very* quick check of a P2 XR-E. WOW!

The Vf at 700mA was in the range of a very low H bin or a high G bin!

If the output was mid-point within the bin range, at 700mA the output would have been equivalent to a V-bin Lux!

These things are incredible - the excitement is justified!

 

[glire]

Crazy CPF influence !
Instead of simply speaking in "volts" or "lumens" they speak in "bins"
So you got a LuxIII like VX1G bin, great !

 

[MillerMods]

I did a *very* quick check of a P2 XR-E. WOW!

The Vf at 700mA was in the range of a very low H bin or a high G bin!

If the output was mid-point within the bin range, at 700mA the output would have been equivalent to a V-bin Lux!

These things are incredible - the excitement is justified!

I wonder if the Vf will be even lower if they are burned in.

 

[Anglepoise]

I must have a bad P2 as the one I tested at 750 ma was Vf 3.67.
Fkuke meter.

 

[MillerMods]

I must have a bad P2 as the one I tested at 750 ma was Vf 3.67.
Fkuke meter.

No binning for Vf... yea, that's a bit of a problem. I guess one could buy lots of these and bin them by Vf and sell them at a premium though.

 

[milkyspit]

No binning for Vf... yea, that's a bit of a problem. I guess one could buy lots of these and bin them by Vf and sell them at a premium though.

I've tested a couple 10-packs of P3 bin at 350mA on my regulated PSU... from a single 10-pack I'm typically seeing a low Vf around 3.11V and high Vf around 3.48V. IMHO that's a pretty broad range! oo:

 

[Archangel]

I've tested a couple 10-packs of P3 bin at 350mA on my regulated PSU... from a single 10-pack I'm typically seeing a low Vf around 3.11V and high Vf around 3.48V. IMHO that's a pretty broad range! oo:

Is that "worse" than you'd get if you grabbed ten random luxeon that were binned only by output?

 

[Christexan]

I don't know the details on what kind of circuit a "flupic" is, but my understanding is it's more of a complete "circuit" regulator (parts mounted on a board), rather than a discrete single part such as the linear regulators below (one single package). Could be wrong, but that's my understanding, you could build a flupic from separate parts, a linear regulator IS a single part (externally, internally there are several transistors, protection diodes, resistors, etc, but on a "microchip" level, not a discrete component level).

LDO is "Low dropout", a term used in comparison to a standard voltage regulator. Most commonly...
LM317 (adjustable)/LM78XX family (and many others) - these are standard "linear" regulators (basically work by throwing out excess voltage/current to achieve the desired voltage/current output, kind of a "brute force" "buck" method (cannot boost either number above what the source puts out). Typically drops about 1.5V internally (1.2-2.0V neighborhood depending on output) in operation (regardless of output desired), in addition to whatever additional drop is needed to achieve desired output.

LM108x family - does exactly the same thing as the LM78xx/317 family, however uses a different internal transistor configuration to achieve around 0.5V drop (therefore "dropping out of regulation" one volt lower than the previous models, hence an "LDO") in voltage (0.2 to 1.0 neighborhood depending on output levels). This gives you a "free" volt on average to play with in your design (3.3Vf LED with 4 NIMH batteries (4.8V nominal) leaves 1.5V to deal with... an LM317 would use all that out of the box (well, not exactly, but "nominally"), so you'd get little benefit over using it over just dropping another 1.5V with another type of diode. But put an LM1086 in there, and it leaves you one extra volt, now you get some runtime before the regulator becomes extraneous.

LM78 family runs around $0.32 at mouser.com per unit, LM108X runs around $0.98, so that's why someone with a high volume usage and modest power considerations could save money with the more wasteful version, however for any battery operation like CPF users would be concerned with, the extra 66-cents is worth the extra usable volt from the source.

 

[LightBright]

[Parallel operation]
There will be serious issues when operating several XR-E in parallel.
Vf vs I curve is so flat that even a small difference in Vf results in big difference in current.

I do not know how consistent the Vf-I curve is within a production batch, but even 0,1V difference yields 100-150mA difference in current below 700mA.

You're right about the situation being bad if you run them in parallel - SO DON'T DO IT!! Run them in Series. Yes, you will need a high voltage supply.

I just got some P2's. Wow- I am impressed by the relative lack of heat buildup yet the very good light output! At 1 amp the Vf was about 3.6ish

 

[IsaacHayes]

Christexan, thanks for the most excellent explanation!!
LightBright, or if you can't do series, have a resistor/circuit for each single led.

 

[LightBright]

Yep, but resistors in a flashlight circuit - not so great for overall efficiency, especially as the power driven through the LED (Luxeon 1, 3, 5 watt or Cree XR- E) increases.

 

[Christexan]

Isaac - Your welcome.
Parallel isn't so bad, so long as it's CURRENT regulated (not voltage), and the Vf and current specs of each LED at the operating current is well within max limits (not overdriving any of them outside of ratings or thermal envelope).
You might however see visible output differences in that scenario. Adding low ohm resistors would help even it out some, yes it's wasteful, but high series voltage may not be an option, and small resistors (say 1 ohm or less) won't waste much power, but will definitely stabilize things.
If your LEDs individually at 500mA range from Vf of 3.3 to 3.6, and the LOWEST one (say the 3.3 in this case) runs at 700mA at 3.6Vf, then you are still within spec so long as you can keep the heat from escalating. Brightness will DEFINITELY vary however in this scenario.
In other words, choose the current you wish to operate at, and you have a few choices..
Option 1 (riskiest but reasonable): Find the LEDs voltage range at the desired current (say 500mA)... ranked from high to low (use 3.3 low to 3.5V high as an example). Take the highest Vf LED rating (at test current).. for example, 3.5V... now run the lowest Vf LED at 3.5V (ramp up to avoid burning it out) and see what current it pulls. If it's still within safe margins (say 600mA), then you can run them in parallel, so long as you are current regulated. (Pushing lower LEDs to match highest while keeping in rated specifications, brightness COULD vary significantly)

Option 2 (very safe): Find the range, and test the highest Vf (3.5Vat 500mA) LED, but test it at the voltage of the lowest rated LED's Vf at 500mA (3.3V)... Set the current to whatever current makes the highest rated Vf LED equal to the Vf of the lowest rated, and almost no chance of problems (Limiting the circuit to the lowest end denominator, dimmer performance likely in this case, and varying brightness of LEDs)

Option 3 (best safe performance) : Test LEDs Vf range, put resistors on all LEDs ("resistor match" them), adjusting resistance to match current levels at a given voltage (I'd choose a tiny bit more voltage output than the the top Vf, and work back from there). So put say a 0.2 ohm resistor on the top LED (just to be safe, all the LEDs should have some resistance, or none, otherwise you might have problems (the non-resisted ones would have a nonlinear resistance curve to the rest of the set)). This gives a regulator output of 3.6V to drive the top LED at 3.5Vf. The 3.3Vf LED should have a resistor of 3.6-3.3 = 0.3/.5A = 0.6 ohms
Losses to resistance (in this 2-LED case for example) would be small if you start with small enough resistance. In this example, if it were just these 2, you'od have .1*.5=.05 watts (tiny) plus .3*.5 = .15 watts. Total loss of 0.2 watts, plus maybe a little more loss from driving the regulator 0.1V higher. Anyhow, you can use smaller resistors to reduce this further assuming you can find them smaller (or make your own).

 

[win67]

Received my sample from Cree today.
The sheet says it is Bin number: xr7090WT-U1-WG-P3-0-0001.
Looks a little bit on the greenish side compared to my hds xrgt.
Put two crocodile clamps to it and powered it with a used duracell cr123.
Lights up the isnide of my wardrobe very well (broad beam) and doesn't get hot at all (no heatsink used)
Thank You, Cree!

Jens

 

[srvctec]

Parallel isn't so bad, so long as it's CURRENT regulated...(edited to save space)

:goodjob:

Thanks for the detailed info!! I've learned a lot from your posts in this thread. It's easy to understand and well explained. :rock: