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PostPosted: Tue Jan 15, 2013 1:13 am 
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Joined: Mon Jan 14, 2013 11:36 pm
Posts: 9
http://www.ti.com/product/ptr08060w
http://www.mouser.com/ProductDetail/Tex ... xpxNOoc%3d

When I first started looking at aquarium lighting, I really wanted to build an LED setup. It turned out to be much more expensive then I anticipated, so at the moment it's unfeasible for me to try. In the future, I expect that I will be perusing this idea more. This regulator is available in 6A and 10A models and runs about $12-$15 respectively on mouser. That should be enough power to drive more then a few 3W LED's I think. The output voltage is adjustable by changing the resistance between the V set pin to ground. Only other parts required are a couple of caps. I have used one of these chips in making a variable output e-cig and it performs very well.

I think this thing would make an excellent LED driver/dimmer module. It's cheap, tiny, efficient, stable, and accepts a wide range of input voltage. I was thinking about using a digital pot and an arduino to automatically control the regulator for LED dimming.

What do you guys think?


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PostPosted: Tue Jan 15, 2013 2:03 am 
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Joined: Sun Dec 30, 2012 5:48 pm
Posts: 21
LEDs need to be current controlled, not voltage controlled.

Once you get to the Vf (forward voltage) of a LED, a very small change in voltage makes a very large change in current.

Knowing that alone, you might think that by carefully adjusting the voltage, you can still get the current you want. Which would be true if it weren't for another characteristic of LEDs. As the temperature increases, Vf drops. Which means more current. More heat. Resulting in more current still. And so on. This is known as thermal runaway.

You haven't run into this problem with the heaters in your e-cigs because they act exactly the opposite as LEDs - as they heat up, resistance increases. So no thermal runaway.

Now since you'll be using an Arduino and a digital pot, if you also measure the actual current through the LED, and continuously adjust voltage based on both the current and the desired brightness, you have indeed created a current controlled power supply. Although it's a bit risky doing it this way. If your code is buggy or Arduino crashes, it could burn up your LEDs.


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PostPosted: Tue Jan 15, 2013 2:19 am 
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Joined: Mon Jan 14, 2013 11:36 pm
Posts: 9
I hadn't dug too deep into controlling LEDs and I guess I incorrectly assumed you could control them by adjusting the voltage. Something like this probably wouldn't make a very good LED controller then. I had wondered why I hadn't seen anyone talk about using something like this for driving LEDs before. Thanks!


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