Controlling high brightness LEDs

M

mick

Active member
Hi there,

I'm currently working on a project where I'd like to slowly fade the brightness of a series of high brightness RGBW LEDs.

Basically I'd like to drive these 4W (1W per channel) current-driven LEDs:

Screenshot 2022-04-20 130420.png

https://www.lumitronix.com/en_gb/smartarray-q4-led-module-4w-rgbw-4000k-cri-90-32454.html

What surprised me was that they only require 3V, and then I learned that with these types of high intensity LEDs, the voltage is not important, but the (consistency of the) current is.

I looked a long time for a suitable LED driver, and ended up buying one of these, which can take in 5-36V and provide a stable current.

colibri-driver-for-power-led-rgbw-7305-colibri-500x500.jpg

https://store.open-electronics.org/colibri

Which also came with a long article explaining the usage of high intensity LEDs

https://www.open-electronics.org/colibri-driver-for-rgbw-leds/

Normally people use LED drivers in combination with a whole series of them. Though in my case, I want to drive 54 of them, in pairs of 2. (ie, 27 "unique" LEDs with each 4 channels (RGBW)).

The test setup I have works well:

- Teensy 3.5
- Adafruit 16 channel PWM https://www.adafruit.com/product/815 (going with this to have enough PWM pins to control all 27x4 channels)
- Colibri 4 channel PWM controlled LED driver
- 1x high intensity RGBW LED 4W

My main questions is, does anyone have experience with powering these types of LEDs? And are there alternatives to using the Colibri? I was surprised that there seems to be hardly anything out there. Especially something which can support more channels (there's a lot of single-channel LED drivers out there).

Screenshot 2022-04-20 130005.png

Above you can see my hardware setup, it seems crazy to need an LED driver per LED.

If anyone wonders why its important to have constant current, its to prevent the LEDs from flickering. Using an LED strip for my project is also not an option, each LED needs to sit at the end of a 2 meter cable and light up an acrylic rod.

Any help or suggestions would be greatly appreciated!
 
mick said:
My main questions is, does anyone have experience with powering these types of LEDs?
Click to expand...

Many years ago I worked on a similar project for Burning Man friends, which used 90 RGB LEDs to light up acrylic rods. I believe each LED was 10 watts. Not a lot of info remains from that old project, but here's a photo of the hardware I built back then.

led5.jpg


90 of these LED drivers were built. It was incredibly bright. The LEDs get hot when run at full power, and the 3 driving transistors also heat up because it's not a switcher, so the whole thing needed to be mounted to a large piece of aluminum.


And are there alternatives to using the Colibri?
Click to expand...

That sort of constant current driver will be the most efficient way. I'm a little surprised it does not have a large capacitor on its input power. These sorts of buck switching power supplies draw pulsing current at their input. If you use these, I'd recommend buying at least 1 low ESR capacitor for each and connect it right at the input terminal block, so you're not delivering large rapid pulsing current down wires of 2 meter length.

If you can afford to waste a lot of power, and if you're willing to solder a lot of circuitry, you could build linear drivers like I did for that old project. Each LED needs a NPN transistor, an opamp, and a couple resistors.
 
Hi Paul,

Thank you for the excellent advice and examples! Apologies for getting back to you so late. I became a dad very shortly after that post, so everything hardware related stayed in the shelf for a bit.

I think I'm going to play it safe with this one and stick with the Colibri LED drivers. The lighting behavior essentially has to recreate the movement of the sun, so it won't be doing any crazy light strobe effects.

Once again thank you for giving some input. I'll post some photos once its put together.
 
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