XM-L2 maximum forward voltage not specified?

I'm looking over the Cree XM-L2 datasheet: http://www.cree.com/~/media/Files/C... Modules/XLamp/Data and Binning/XLampXML2.pdf

And I notice Cree specifies a maximum forward voltage of 3.15V @ 700mA, but not for higher current levels. They specify typical values @ 1500 and 3000mA, but again, no maximum values.

What am I missing here?

I see the graph on the data sheet lists the Vf as being about 3.3 volts at 3 amps, on page 4

jason 77 said:

I see the graph on the data sheet lists the Vf as being about 3.3 volts at 3 amps, on page 4

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Yes I noticed the graph, although this seems to be typical Vf values.

I suppose with the variation between individual emitters they cannot predict exactly how much a given LED will drop at every current level. I was just hoping for an easy "max" Vf I can use to ensure my driver doesn't run out of voltage at any current level.

It's pretty common to specify max values of even very important characteristics for only certain conditions, which aren't how many people want to use the part. I design electronics for a living, and I see this all the time.

Only very recently have LED makers started posting specs at 85C junction temperatures. Before that, they went out of their way to test under unrealistic conditions - 25C junction temperature, which isn't achievable in the real world, at least in most cases.


I applaud the LED industry for moving to specs at 85C, now if they would post Max/Min values at realistic drive levels, we could all live happily ever after.

Glad to hear it's not just me then! Thanks

creyc said:

What am I missing here?

Click to expand...

I can adjust this value by controlling LED temperature, LED age, and exact specimen of LED. Some manufacturers also sort theirs by forward voltage bin. Cree does not. Some clever electronics measure LED temperature change by comparing the present forward voltage to what it was at turn-on. Some clever LED modders 'burn in' their LEDs to reduce Vf in direct-drive lights and get more lumens. And some people sort their own LEDs to use higher-Vf ones with less-bleeding-edge projects.