Drivers capable of running short strings of High Power LEDs efficiently

[Sailfish]

Hi!

This is my first post on this forum, whoop!

I need drivers capable of running short strings, 1-3 LEDs, of 3W high power LEDs efficiently.
I will be using 3W Cree LEDs, premounted on aluminum stars. The LEDs, will be driven at Vf 3.2-3.5V and If 0-1000mA.

My plan is to connect all the drivers to an Arduino controller, to be able to program the output of the different LED strings, meaning I want to control the drivers with PWM signals.

What kind of drivers should I look at?

[_pike]

http://www.pcbheaven.com/userpages/high_efficiency_high_current_led_buck_driver/

Here you are.......read it all and the solution you are looking for is at the second page.One chip for 1 array of 3*3W leds


ps: Almost forgot....Welcome to the forum!!!!!

[kam]

3W x 3 leds = 9Watts??? this is the case?

[Sailfish]

http://www.pcbheaven.com/userpages/high_efficiency_high_current_led_buck_driver/

Here you are.......read it all and the solution you are looking for is at the second page.One chip for 1 array of 3*3W leds


ps: Almost forgot....Welcome to the forum!!!!!

Nice, thanks for the link!
I will read it carefully this weekend 

Thanks!

3W x 3 leds = 9Watts??? this is the case?

This would be the longest of the strings. I will have different length strings depending on the number of a certain wavelength LED I need.
For example:
1st. string: Neutral White-Neutral White-Neutral White
2nd. string: Royal Blue-Royal Blue-Royal Blue
3rd. string: Cyan
4th. string: Red
5th. string: UV-UV

[kam]

What is the lowest and the highest wattage that you want to control? This way we know what is the max power you want to dissipate and if it is possible with a single driver

[Sailfish]

What is the lowest and the highest wattage that you want to control? This way we know what is the max power you want to dissipate and if it is possible with a single driver

The lowest wattage would be 3W (1x3W LED) and the highest wattage would be 9W (3x3W LEDs), as you suggested earlier 

[kam]

So, roughly roughly, you need to dissipate at least*** 6 watts of power....

***At least means that you may have to dissipate more to have a stable brightness. So, this is NOT "efficiently" as you suggested. There is only one way to do this efficiently, and this is with a buck converter. Of each of your LEDs requires 3.5V max, you will use a 3x3.5=10.5 (plus a few volts to increase switching speed) some 15-20 volts (or more of course). Then, you use a buck regulator with constant current output regulated at 1000 mA. You connect the LEDs in series and then connect this string to the output of the buck regulator. You can turn off an LED and keep all the other LEDs on simply by bridging its connectors. The regulator will then "see" this change and it will regulate the current again to 1000 mA.

I have used the A6210 for a similar project, able to drive up to 80Watts of LED with very high efficiency. It can operate up to 42V and deliver up to 3A of current. PLUS it has a PWM input which you can use to efficiently dim the LEDs. Here is a sample circuit:
http://www.pcbheaven.com/userpages/high_efficiency_high_current_led_buck_driver/

(i think i've given it to you already  )

Where is the catch? The catch is that this driver comes only in QFN package. If you don't have a hot-air gun for re-flow works, you really don't wanna mess with this package. I used a QFN16 to DIP 16 breakout PCB to test in on the breadboard so don't be fooled by the images. The QFN is small, 4 by 4 mm in size and has 16 pads...

You can search for another similar chip in bigger package

[Sailfish]

So, roughly roughly, you need to dissipate at least*** 6 watts of power....

***At least means that you may have to dissipate more to have a stable brightness. So, this is NOT "efficiently" as you suggested. There is only one way to do this efficiently, and this is with a buck converter. Of each of your LEDs requires 3.5V max, you will use a 3x3.5=10.5 (plus a few volts to increase switching speed) some 15-20 volts (or more of course). Then, you use a buck regulator with constant current output regulated at 1000 mA. You connect the LEDs in series and then connect this string to the output of the buck regulator. You can turn off an LED and keep all the other LEDs on simply by bridging its connectors. The regulator will then "see" this change and it will regulate the current again to 1000 mA.

I have used the A6210 for a similar project, able to drive up to 80Watts of LED with very high efficiency. It can operate up to 42V and deliver up to 3A of current. PLUS it has a PWM input which you can use to efficiently dim the LEDs. Here is a sample circuit:
http://www.pcbheaven.com/userpages/high_efficiency_high_current_led_buck_driver/

(i think i've given it to you already  )

Where is the catch? The catch is that this driver comes only in QFN package. If you don't have a hot-air gun for re-flow works, you really don't wanna mess with this package. I used a QFN16 to DIP 16 breakout PCB to test in on the breadboard so don't be fooled by the images. The QFN is small, 4 by 4 mm in size and has 16 pads...

You can search for another similar chip in bigger package

This sounds intimidating, yet I am very intrigued. 
Actually I have a hot-air gun for reflow works on my soldering station, but I haven't used it before.

This seems like a very nice challenge!

[cheerio]

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=310405195072
these should work too. if you need more than 1.5A you can use an external mosfet. (datasheet says so)