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So this is probably a noob question but ive never used this kind of driver for my LEDs before. I'm wondering what you have to do with a constant current driver to like set the voltage. I plan to use 3 drivers for a 30 watt RGB led, the specific items are below. The drivers have a voltage range and I'm wondering how it knows how much voltage to supply. It doesn't make sense that the blue and red channels would be set up exactly the same because it seems like either the red would have too much power and burn out or the blue would not have enough. It seems like I should have to put something between the driver and the LED to keep too much power from going to it. BTW I'm going to put a mosfet between the driver and led so that I can control the color with pwm from the arduino. Sorry for my dumb question but thanks in advance

http://www.dealextreme.com/p/pa38-led-27-42v-dc-320ma-constant-current-driver-circuit-85v-265v-ac-13691
http://www.dealextreme.com/p/30w-1500-lumen-rgb-led-emitter-metal-plate-39960
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The drivers have a voltage range and I'm wondering how it knows how much voltage to supply.

Because the drivers are constant current drivers, they will automatically raise or lower the voltage to maintain the constant current value. That is there function in life.


 It doesn't make sense that the blue and red channels would be set up exactly the same because it seems like either the red would have too much power and burn out or the blue would not have enough.


Yes it does make sense, again the constant current output of the driver module is what controls the specific current avalible to the LEDs regardless of their specific voltage specifications, that's what a constant current driver brings to the table. The led can not 'force' the driver to supply more current then it is setup to supply to the load.

 It seems like I should have to put something between the driver and the LED to keep too much power from going to it.

That is what the constant current driver is already doing for you.

 BTW I'm going to put a mosfet between the driver and led so that I can control the color with pwm from the arduino.

That may or may not work, depending on the specific constant current driver in question. Some driver modules have a seperate signal input pin for applying a PWM signal and therefore turn on and off the driver current via the PWM signal. Sometimes the pin is called "enable". Perhaps the datasheet for whatever constant current driver you use will give examples of how to use PWM control on it?



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Thanks for the reply, that makes more sense now. Haha it will still be scary not to have something extra protecting my precious leds like I'm used to though. The driver is very cheap (which is why I chose it) its like 7 dollars, I'm pretty sure it doesnt have the enable function though I could look for one that does. I dont see why it wouldn't work to just put the transistors between the driver and LED. Can you enlighten me?
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Can you enlighten me?

Perhaps interaction of the PWM switching frequency will make the driver unstable? Again If it was me, I would check out the drivers datasheet to see if they have a recommended method of using it in PWM service, or I would select a driver that has a PWM signal input and save yourself the expense of having to add a mosfet. That second method is what I did for the 3 watt driver I purchased a couple of years ago. Not the one I bought, but the below driver has a PWM input signal pin avalible to utilize. They also sell other modules of different current levels.

http://cgi.ebay.com/3w-LED-Driver-MBI6651-based-Luxeon-White-Green-Blue-/250847641454?pt=LH_DefaultDomain_0&hash=item3a67af3f6e
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