High Power LED System Driving Method

I am designing a circuit to drive a high power LED system. The system has to drive max. 7 LED strips, each strip has 20 LEDs, each LED is about 3W (forward voltage 3V, 1A). As such, I have drafted two solutions.

For the first solution, please see the attached picture (solution-1.png). I have designed to include a simple constant current source circuit on each LED strip, such as a LM317, to provide the 1A current for each strip. For the power supply, I want to use a AC/DC switching power supply to provide at least 450W, 75V output.

I would like to ask is this system feasible? One of my concern is that can I find an off-the-shelf AC/DC switching power supply to output ~75V, 450W? If not, what is your suggestion?
Another question is if this is feasible, is the LM317 good to be a constant current source in this circuit?


For the second solution, please see attached picture (solution-2.png). In this solution, each LED strip is connected with a off-the-shelf AC/DC constant current source. Therefore 7 strip will need 7 source. This will be rather bulky.

Also, is this system feasible? To switch on/off the LEDs by a micro-controller, I will need to use a solid-state-relay to switch the AC power of the strip, I am not sure if this will has any problem because the load (the constant-current-supply and the LED strips) is not a linear load. (I am not switching a PWM signal, I only need to switch a very low speed on and off sequence).

In your opinion, which solution is better? What is their pros and cons?

Thank you very much for your help!

Hi,

3W x 20 x 7 = 420W LED power
So with a bit of margin the 450W are correct.

75V, at 1A x 7 strings makes 525W. A 450W supply is not sufficient, because your constant current circuits generate
525W - 420W = 105W of heat.
(This is a lot of heat. My soldering iron generates just 30W of heat)

Because of safety reasons I recommend to use a power supply according SELV with output voltage <=60V DC.

There are plenty, cheap LED power supplies with high safety standard.
Where do you see the benefit to build your own power supplies?

Klaus

I am not going to build my own power supply, if I go for solution 1, I will still try to find an off-the-shelf power supply with 75V output. (But I am not sure if I can find one...so this is my concern).

Yes you are right that the constant current circuits will generate lots of heat. And thank you for reminding me the SELV thing.

It seems that the solution 2 is more reasonable in this situation. I am just thinking that I will need one LED power supply for each LED strip, so I will have 7 LED power supplies in the system. However my biggest concern for solution 2 is that I need to switch all the LEDs on and off by a micro-controller with a 10s period. Is it good to use a solid-state-relay to switch the AC input of the LED power supplies?

Hi,

Try to find LED supplies with control input.
Some have digital inputs, some have 0...10V inputs.

Klaus

How will you cool the LEDs that are operating at their absolute maximum power? Won't they blind everybody?