Measure current to LED? ADDED: Cree XCB3590 image

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ChrisR
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Post by ChrisR »

I was forgetting, you need to use the back of your finger in case the thing is at mains voltage, or rectified mains up at 300VDC. Your muscles make your hand come away then instead of onto the component - or so I'm told ;).


Oh - another bit of sage lore, if it's a soldering iron or something which might be very hot - SNIFF IT !
Chris R

Charles Krebs
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Post by Charles Krebs »

ChrisR wrote:Brilliant! But I'd probably put my finger on it to see how warm it feels...
Chris, This LED COB is different from others I have used. It is completely built onto a ceramic substrate. When you look at the back there is no metal in sight, just a single piece of smooth white ceramic.

From a Cree CX family Design Guide
http://www.cree.com/led-components/medi ... _guide.pdf

<< The back of a ceramic substrate CX family LED is ten times smoother than the back of the aluminum substrate often used by other
chip-on-board (COB) LEDs. A ceramic substrate enables a better thermal contact with a flat, clean heat sink. Figure 11 demonstrates the
flatness difference between a CX family LED and a metal-core printed circuit board (MCPCB). >>


So my "finger test" where I touched the corners and edges of the ceramic base and found it just "warm" (but not "hot") was quite reassuring. (And my thermocouple thermometer, while inexpensive, is properly connected to the Tc measurement pad. In the past it has always seemed reliable and sufficiently accurate).

As I mentioned, at this point (depending on the final use configuration) the heat experienced from the light output itself will need some consideration. From the same PDF mentioned above:

<< CX family LEDs transmit no significant IR light, but, as do all high-powered light sources, do transmit significant photonic energy that, if
absorbed by the lens material, can cause the material to heat up. The focusing effect of the lens material can cause the lens to reach a
temperature higher than the Tc of the CX family LED producing the light. >>

Charles Krebs
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Post by Charles Krebs »

Still playing around with that "water cooled" Cree XCB3590. Powering at a voltage where it just started to "glow" I found the pattern of the individual dies interesting. Here are images of the LED off, and another just barely illuminated. Still amazed at the cooling efficiency of the small water block.

Image

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