Driving multiple high power LED's

Thread Starter

PickyBiker

Joined Aug 18, 2015
88
I want to drive multiple 100W RGB LEDs but need information on how to do that.

Each individual color draws (with some variation) roughly 1/3 of that 100 watts. So, if I get a 100 watt constant current LED power supply, and hook it up to all 3 at the same time, all should be good and I'll get white light. Now if I hook up that same PS to just one of the colors, does it turn the LED into smoke or will the LED only draw the current it needs?

If the power has to be limited to the correct current for each color, how is that done in a way that I can switch the colors on and off individually? Does it take 3 power supplies? Can this be done with a single power supply that use PWM to control brightness? For example if 3 colors are on, 100% duty cycle is okay, but if only one or two colors are on the PWM would be limited to 33% or 66% respectively?

Obviously I need some help understanding the finer points of powering LEDs.
 
Last edited:

Reloadron

Joined Jan 15, 2015
5,667
Got the LED data sheet? Going to need that. The data sheet will tell you the Vf (Forward Voltage) and If (Forward Current) of the LEDs. With that information the power supply details can be worked out. The power of 100 watts is going to be the Vf * If but a data sheet is needed just as a start.

Generally and less the details LEDs as you describe are switched using devices like a MOSFET. When using a RGB (tri-color) LED additional colors are made by combining two colors, for example Red and Green would give you Yellow. Then you can use PWM to mix colors and as you mention control brightness. There is more to it but it begins with the LED Data Sheet for what you have or plan to buy.

Ron
 

Thread Starter

PickyBiker

Joined Aug 18, 2015
88
We have the power requirements but that alone doesn't answer the questions.
Here's a simpler example:
The PWM output power supply can deliver 100 watts and is current limited. The led green color draws 33 watts. The 33 watt Green LED color is connected to that 100 watt power supply and the power supply output PWM is at 33% duty cycle.

Does that work or does it fry the LED?,
 

Reloadron

Joined Jan 15, 2015
5,667
No, you would not divide the 100% by 3. If each color is 33 watts you PWM each color 0 to 100%. Here is a smaller scale example:
5050 LED String.png

On the left is an example of 3 RGB leds in each group with a series resistor. Normally if you have a 100 watt RGB LED it does not mean each color is 33.3 watts. In the example the LEDs share a Common Anode of +12 Volts. The RGB Cathodes are each driven by a MOSSFET individually. Each MOSFET can be PWM driven 0 to 100%. Some LEDs share a common cathode and the anodes are switched.

You have a 100 watt supply and if in your case each color draws 33 watts you would be running full power. The LEDs are current driven devices. If a 100 watt supply is PWM at 33% the output current is 1/3 of maximum. In the above drawing any of the three DIO1, DIO2 and DIO3 can be PWM driven 0 to 100%.

Ron
 

Reloadron

Joined Jan 15, 2015
5,667
So, if I get a 100 watt constant current LED power supply, and hook it up to all 3 at the same time, all should be good and I'll get white light. Now if I hook up that same PS to just one of the colors, does it turn the LED into smoke or will the LED only draw the current it needs?
It will only draw the current it needs.

Ron
 
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