Have a 36V 10A Power supply supply that I want to use to drive 3 x 100w RGB LEDS. Each LED color takes a different voltage. Red = 24v, green = 34v and blue = 33v. Each color must be limited to 2.1 amps. So what I need is some kind of circuit(s) that can be added externally to my power supply so I get the following 3 outputs.

24V 2.1 Amps for 3 red LEDs
34V 2.1 Amps for 3 Green LEDs
33V 2.1 Amps for 3 Blue LEDs

Here is what I would "LIKE TO HAVE" in priority order:

A different approach to powering these three legs of the RGB LEDs.
Some inexpensive device I can purchase that can take 36v and have a variable output from 24v to 34v at 2.1 amps
A circuit design so I can build one myself

All ideas welcome

 

Here's a simple constant-current circuit that keeps the current at ≈2.1A as the LED voltage varies.
The LTspice simulation below shows the current nearly constant at 2.145A for a simulated variation in VLED voltage from 24V to 34V.
The N-MOSFET must be a logic level type with a maximum Vgs(th) threshold voltage of <2V.
Note that the MOSFET can dissipate up to 25W so it will need to be on a good heatsink (perhaps with an attached cooling fan)

 

Wow, that look awesome and really easy to build. Got the parts for 3 of them on order now.

Thank you.

 

Wow, that look awesome and really easy to build. Got the parts for 3 of them on order now.

Thank you.

Just realized the IPS040N03L MOSFET cannot be readily connected to a heat sink.
You need one with a TO-220 case or similar such as this.

 

That's a great approach, which supplies constant current for the various voltages. I haven't been doing electronics very long, but here is my naive approach. I sounds like you want to wire each color separately, so this should work. I couldn't find an LED in pspice, but it would be located between R3 and ground. These are the R values for 34V at 2.1A (or very close to it). R2 dissipates nearly 20W. Resistance values for the other two colors are simple enough to calculate with R3 being ~15.7 and ~11.4 for 33v and 24v.

 

That's not a good circuit, as you want all the current to go through the LED for best efficiency.

If you just want to use resistors, all you need is one resistor of the correct value in series with the LED.

 

Yes, it would be easier to put a heatsink on the IPP80N04S4-04. Got 3 of them on order.

Thanks.

 

Yes, it would be easier to put a heatsink on the IPP80N04S4-04. Got 3 of them on order.

Why are you shouting?

Note that the power dissipated depends upon the LED voltage, which is highest for the lowest voltage, so you don't need as big a heatsink for the high voltage LEDs.
A simulation showing the MOSFET power dissipation versus LED voltage is below:

 

Why are you shouting?

Sorry,

The shouting certainly was not intended. I suspect it was because I copy and pasted the IPP80N04S4-04 from a web page and then added the text where it may have simply continued on with the same font.

Yes, I see the need for a good heatsink on the low voltage circuit. Thanks.