Developed a constant current source to drive my power LEDs

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Xindy
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Joined: 15 Mar 2018, 05:59
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Developed a constant current source to drive my power LEDs

Post by Xindy »

I'm playing around with workplace illumination and have developed a 20 V –> 38 V PWM'able constant current source to drive my power LEDs (max power about 64W). So far, so good. However, I've nearly thermally killed one LED by fixing it on a significantly undersized heat sink ("luckily", the wire contacts unsoldered themselves just in time, stopping the process).

Now, I'm considering cooling options. Wanting to avoid active cooling (i.e. the humming of a fan), I was considering the "lazy" way out (dimension far from final, I don't have a heatsink candidate yet):
Image

I'd like to mount the 19 x 19 mm LED directly onto an aluminum bar or profile. Now, I'm already playing around with thermal simulation software, but that seems over the top (and so far, it mostly crashes, plus I have a lot of theory to catch up on). So:

Is there a well-known analytic model for heat distribution when attaching a constant-power heat source to a piece of metal?
if not, is there a go-to simulation software? So far, I'm playing with Elmer.
Is simulation the way to go here, at all, or is passive cooling for 60W LEDs?

Data (from LED datasheet):


Junction-Case Thermal Resistance 0.8 K/W
19x19 mm
max rated power 64.2 W
continuous power I'm planning to use: 36.6 V · 0.72 A = 26.352 W
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Developed a constant current source to drive my power LEDs

Post by mzenker »

Hi,

AFAIK there are estimation formulas for cooling of electronic parts with heat sinks. You might get more information on websites of heat sink vendors, for example here: http://www.fischerelektronik.de/en/serv ... -heatsink/.
Setting up such a model with Elmer is not very difficult either, in principle. You need a CAD model, mesh it, set material properties and boundary conditions (this may be the most delicate part since you need to make certain assumptions), and run the solver. If you have the time ( would say a day or two for a newbie, depending on the learning speed), it can be fun to do it. You will get a more detailed result.
But normally putting the LEDs on a heat sink of sufficient size and see what happens should get you quite far...

HTH,

Matthias
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