Luxeon current draw. Help.

[yaesumofo]

These are the numbers:

Data: 3.5v 3.47v 3.51v 3.6v


TXOK#1 .39ma .53mA .62mA

TXOK#2 .35 .45 .53

TXOK#3 .45 .59 .70

TXOK#4 .53 .69 .80

TVOJ#1 .87 .95 .82 1.3

TVOJ#2 .63 .72 1.10 .99

Here are the current figures of what these emitters draw when connected directly to a Bench power supply.

It seems to me that these numbers should be more consitant. Each LED is different. The 4 TX0K's are all connected to each other in rack form.

How come the current draw is not more consitant? Does this curent draw correspond with the brightness of the LED's?
Does this mean that we really are looking for low (Vf) bins and hoping that they draw the maximum current?
Yaesumofo

 

[NewBie]

What you really want to know is how many WATTS in it takes to make X Lumens. Got an integrating sphere?

Watts = Vf * Amps

Vf or amps is only half the story. You need the whole thing , watts, to determine efficiency- plus the actual lumen output.

According to the LumiLEDs instructor, the Luxeon 1W LEDs are binned with the die at 25C, by brightness, color, and forward voltage at 350mA. The forward voltage will vary alot between LEDs at currents other than 350mA, as the curves are not identical for each LED, and can be drastically different at other current levels.

Since these are LuxIIIs, seems you'd need to put 700mA into each one, while holding the die at 25C, and then measure the Vf to see if they fall within the bin requirements.

http://www.lumileds.com/pdfs/protected/AB21.PDF
Bin K 3.51-3.75 Vf at 25C die temp
Bin J 3.27 - 3.51 Vf

Measurement Charactertistics, Page 4, http://www.lumileds.com/pdfs/protected/DS45.PDF

Electrical Characteristics at 700mA, Junction Temperature, Tj = 25oC

 

[robk]

It has been my experience that every LED is different. So, knowing that, I totally ignore Vf and adjust the driver (direct drive resistor or sense resistor in a converter) for proper or desired current. Works for me! These are current devices, Vf is only relevant if you are direct driving with no resistance.
Rob

 

[Klaus]

Yaesumofo,

your numbers somehow make sense and then not so too

That a "J" Vf draws more current at the same voltage from a bench supply than a "K" makes a lot of sense - by design - this is what the "Vf" actually is telling us. For the same current draw it will need a lower voltage.

I´m a little confused with 4 voltage numbers and three current draw figures though, typically the current draw should increase with voltage, some of your number look different as if a higher voltage gets you less current ?

My experience with measuring quite some stars lately is that within each bin the voltage can and will vary, sometimes even outside the expectecd range, while this seems to have become rather rare with the new binninbg system.

LEDs with the new binning system overall seem to be more "EQUAL" than before I was told from people receiving the newer ones and had more experience with the old ones too. My experience is that out of blocks of the typical 8 attached stars you will see a tendency either to the lower, middle or higher end of the specifix Vf range, while still within those blocks you´ll see differences.

Looking at the voltage/current curve as documented by Lumiled even a 0,1V Vf difference can and will result in significant current draw differences of 100ma or more - so a LED from the lower end of a Vf range can draw 200-300ma more than one off the higher end of the same Vf bin code at the same Vin, from the lower end of one Vf to the upper end of the adjacent bin code (like J and K) this could be a difference well beyond 500ma at the same voltage - and this seems to be exactly what you are seeing.

I think this is the reason most people would prefer current regulated circuits which are equaling out this difference against voltage controlled or direct drive setups. While you will always get different current draws and subsequent different brightness (not taking brightness bins and lumens/watts into account right now, just raw watts vs Vf) with voltage regulated and direct drive setups - but you will have similar power consumption but differing runtimes when using current controlled circuit setups then. The only flashlights sofar which does even take the final brightness into account are the ARC4 and the upcoming EDCExtrem and EDCUltimate which the ARC4 designer is bringing to market soon.

As for voltage controlled and especially direct driven applications it is very advisable to check each and every LED for the actual current consumption to have no risk of overdriving it but also a good enough driving power for good brightness. This is quite a challenge without a current controlled circuit as seen lately with failing flashlights from CPF modders as well as commercial companies starting to use Luxeon LEDs - especially with direct driven or only resistored designs - and as some of the more experienced hacks on this board would say - its the nature of the beast and you have to live with it.

I hope I could be of some help

Klaus

 

[yaesumofo]

Thanks Klaus.
The fog clease slowly.
I measured the J bins 1 more time than the others.

I have a few more comming so I will do a study of them and try to extrapolate some meaningful data.
Yaesumofo

 

[INRETECH]

Again, LEDs are current devices - completely IGNORE the forward voltage from the equation, just bias the LED for the correct current according to the specs, the LED will find its own voltage

 

[robk]

Inretech-
Precisely what I said, adjust the current and the voltage will fall into place. Why is it so hard for people to realize this?
Rob

 

[14C]

Klaus, current regulation helps to keep the dark out of the LEDs too... /ubbthreads/images/graemlins/smile.gif

VF can change downward. If it does the current will increase and the device can go into runaway with a voltage regulated supply.