Luxeon Star Vf

Doug S

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I have long been surprised at the wide range of Vf@350mA@25C given on the Luxeon Star datasheets for the white/blue/cyan versions. The datasheet range is 2.79-3.99V @ 25 C with a typical of 3.42V. So far, the limited number of samples I've tested [all fairly early production units] have had Vf in the range of 3.07-3.20V under stated test conditions. Note, to properly make this measurement you must either use low DF pulse techniques at an ambient near 25C or actually measure the junction temp and then correct your measured Vf value using the -2mV/C tempco of Vf. My question to the folks here that have tested the Vf of a number of samples, what is the range of Vf that you have seen and what appears to be the "typical". Even if your testing hasn't been very rigorous, please share your data and describe your test setup and perhaps I can infer what the "standard test condition" Vf values would have been. Minimum required information would be Vf, test current, immediate measurement or at thermal SS, degree of heatsinking if any.
 

Doug S

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Originally posted by dat2zip:
Doug,
I have seen a large nomimnal range around 3.1V-3.3V and have heard from others of a few that are as low as 2.9V @ 350mA.

I don't measure it exactly to the degree you are talking about and monitoring the junction temperature.

Rarely, am I driving 350mA. Most of my testing is seeing how much I can squeek out of my DC/DC converters, so, sometimes I am driving 600,700 and 900mA for more than a couple of minutes-WayneY
<font size="2" face="Verdana, Arial">Wayne, thanks for the info. Am I interpreting you correctly that you are measuring Vfs in the range of 3.1-3.3V at test currents in the range of 600-900mA after a couple of minutes?

BTW, I consider 3.1-3.3V to be a "small" nominal range, especially compared to what is given on the datasheet.
 

moraino

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Jan 20, 2002
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B.C. Canada
Originally posted by dat2zip:

I just finished an informal test of the sample 5W I got from Luxeon. With a power supply set for constant current of 400mA, the 5W star was held to the top of an open minimag tube using Arctic Alumina thermal grease. The Star never got so hot I couldn't hold it any more. The computed watts was around 2.4W. I held it there for 2-3 minutes.

-WayneY
<font size="2" face="Verdana, Arial">Sorry Doug, it's off the topic.

Wayne,

Are you going to mount the steroid LS on the MAG 3D body to see if it can take the heat.

I don't think the Mag AA surface is big enough to rid of that much heat. Of course, 2 W should be OK but it's a bit of waste.

Anyway, let us know if you do try it on MAG AA. Keep up the good work.
smile.gif
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Henry
 

dat2zip

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Doug,

I have played with quite a few of them. All my current test conditions are based on the LS/O versions bolted to a large aluminum plate and Arctic Silver 3 thermal grease for good thermal contact.

I have seen a large nomimnal range around 3.1V-3.3V and have heard from others of a few that are as low as 2.9V @ 350mA.

I don't measure it exactly to the degree you are talking about and monitoring the junction temperature.

Rarely, am I driving 350mA. Most of my testing is seeing how much I can squeek out of my DC/DC converters, so, sometimes I am driving 600,700 and 900mA for more than a couple of minutes. If I am working with more than 600mA, I usually turn on a fan to blow air across my board and the LS load. The aluminum plate rerely gets mildly warm under the Luxeon.

I just finished an informal test of the sample 5W I got from Luxeon. With a power supply set for constant current of 400mA, the 5W star was held to the top of an open minimag tube using Arctic Alumina thermal grease. The Star never got so hot I couldn't hold it any more. The computed watts was around 2.4W. I held it there for 2-3 minutes.

-WayneY
 
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