LED Strings and current sharing

[Tantalum]

Hello

I wanted a PCB with 20 CLQ6B-TKW RGBW Leds with 48VDC power supply.
I do not want a voltage boost led driver. It has to be a set-down Buck converter (4 actually). One for each color + white, but as you know 48VDC is not enough.

So the solution would be to parallelize the LEDs, 2 parallel string of 10LEDs @0.2mA for each led driver.
Since every LED has a different forward voltage, will it be a problem???

I mean 10 LEDs in series, statistically, I would say the 2 string will have approximately the same voltage drop, no?

Or will I need to measure the forward voltage of each LED, an select the right ones to create a balanced strings?

[mariush]

Only 20mA on each led?

those leds are rated for almost 200mA on each color, and the forward voltages are specified at 100mA

See bottom of page 2 in datasheet : https://cree-led.com/media/documents/CLQ6B-TKW.pdf

red   : avg 2.1v max 2.6v
green: avg 3.0v max 3.8v
blue  : avg 3.1v max 3.8v
white: avg 2.9v max 3.6v

For red, you could probably have all 20 in series, I doubt the total forward voltage would get close to 2.3v x 20 = 46v so even a linear driver should work fine (need around 1-2v drop inside the linear driver)
for the others, I'd do calculations with a forward voltage of 3.2v in mind .... if you bin them then the two series of 10 should have close enough voltages to work in parallel.
 

You should decide on the max current you're gonna have and then buy maybe 100 leds and bin them at that current you chose, so they're fairly close to each other.

[tooki]

[…]
So the solution would be to parallelize the LEDs, 2 parallel string of 10LEDs @0.2mA for each led driver.
Since every LED has a different forward voltage, will it be a problem???

I mean 10 LEDs in series, statistically, I would say the 2 string will have approximately the same voltage drop, no?

Please explain what you’re trying to accomplish.

Fundamentally, you use current limiting resistors on each string of LEDs, with the resistor selected to drop the “excess” voltage at the desired current.

Look at ledcalculator.net, it illustrates it nicely.

Only 20mA on each led?

those leds are rated for almost 200mA on each color, and the forward voltages are specified at 100mA

Where do you see 20mA? The OP wrote “0.2mA”, but I assume they mean 0.2A per string, as you identified in the datasheet.

[clairemattockskth67]

waiting for an explanation