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Author Topic: high power led driver  (Read 4643 times)
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Hi, I'm trying to build a circuit to control some high power LEDs thru arduino.
The LEDs need about 350mA, current regulated. I'd like to know if there's an IC that does current regulation (to drive the LEDs) and manages the LEDs (I have 5 of them). I know there are many, but I need about 350mA per LED and that's a lot I think.. any idea?
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http://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF
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interesting.. but it's only 1 LED on that IC, do you know if there's something similar but that drives many separate LEDs independently?
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interesting.. but it's only 1 LED on that IC, do you know if there's something similar but that drives many separate LEDs independently?

Well one driver can drive several leds if they are wired in series and the drive has an output voltage higher then the combined voltage drop of all the series leds wired in series. However if you want to control each led independently then each would require it's own constant current driver.

Lefty
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I have an article on driving 350mA LED's on my website:
http://www.elcojacobs.com/using-shiftpwm-to-control-350ma-high-power-leds-with-arduino/
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Take a look at these

BillO

http://arduino.cc/forum/index.php/topic,102101.0.html

reply #7


Boffin1

http://arduino.cc/forum/index.php/topic,132397.0.html
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Super cheap, super easy.  Use a decent wattage resistor, 1/2 watt or more, or calc out the dissipation.  The circuit isn't particularly efficient (3v drop) but it is cheap and easy!

Basically the LM317 acts as a variable resistance limiting the current.  The chip is rated for 1.5A, I'll say that if you are driving more than 500mA you NEED a heat sink.  These are great with a 1.2 ohm sense resistor and connected to 12-14v, it's perfect for driving the 10 watt white LEDs (1A@9-12v) you can get for a buck or two on ebay.  The LM317 is one of the cheapest components you can get, and one of the most useful too.  Buy a pack of them, you are going to want more.

This feeds into the LED, and you switch the ground connection with an NPN transistor to provide PWM.  

I've made a bunch of these.. if quick and dirty is good enough, it'll do the job nicely smiley

Here's the Application Note from ON Semiconductor on using the LM317 this way:
http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF
« Last Edit: December 10, 2012, 12:48:59 pm by focalist » Logged

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The TLC5940 http://www.ti.com/lit/ds/symlink/tlc5940.pdf can provide constant current
upto 120mA per output (set by single resistor for all outputs).  As it has 16 outputs you can parallel
them in threes to give 5 outputs of upto 360mA, and you can program PWM values into it for dimming
(and store them on on-chip EEPROM!!).   Only one device for 5 LEDs then.

You'd need to be very careful not to exceed the power dissipation though - perhaps adding enough series resistance to keep
the outputs around 1.0 to 1.5V (below 1.0 the constant-current behaviour deteriorates, the higher the voltage
the more heat).
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Another constant current driver http://arduino.cc/forum/index.php/topic,123665.msg932376.html#msg932376
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Thanks to you all, in particular the TLC5940 seems a good solution, I hadn't realized I could use more than one output on the same LED. @MarkT, could you clarify this part a bit? would I just need to wire the 3 outputs together and set the same pwm on them? Or maybe I need some capacitors to smothen things up (random guess  smiley-razz)

Thanks
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Quote
350mA,

That's hardly "high power".

3.5a? maybe.
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Quote
350mA,

That's hardly "high power".

3.5a? maybe.


It's all relative DH, after a newby is done blinking his 20ma standard leds, stepping up to a 350ma led is a 'higher power' step up in my book. It's where you have to learn about good constant current control methods and proper heatsinking and wearing sunglasses if you are going to look straight at them.

Lefty
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Thanks to you all, in particular the TLC5940 seems a good solution, I hadn't realized I could use more than one output on the same LED. @MarkT, could you clarify this part a bit? would I just need to wire the 3 outputs together and set the same pwm on them? Or maybe I need some capacitors to smothen things up (random guess  smiley-razz)

Thanks

Well I am not sure - its possible they have separate counters for each output (though this seems wasteful), so you would need to
double check that.  Since the currents add even that might not matter.  Yes, set the PWM values the same for commoned
pins would be sensible.
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I bought one and will try.. but what do you mean by "separate counters"? I know I can set the current individually using the DC (dot correction) registry in the tlc5940, so yes each pin has it's own separate current regulation I guess.. but anyway as you say currents do add, as long as the voltages are the same (and don't flickr I guess..) there shouldn't be any problem.
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A word of caution, while you can get the current within the rating of the chip watch out for the power dissipation running 5 350mA LEDs is going to be very close if not over the limit.
There is a scary looking formular in the data sheet, that needs your circuit values plugging in.

As for our Mr Heny, I don't cair what you call high power, 350mA for an LED is high power. It might not be ultra high power but it is high.
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