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LED CC booster design – feedback needed

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3dgeo:
Hi,

designed 9x15 3528 UV LED matrix driver circuit.
Analog circuits is not my strong side, so I would like to get some feedback on inductor and diode (efficiency is not extremely important as this is not battery powered project).
Inductor: YNR8040-470M or SLD10D40S-330MTT?
Diode: BAT46W or BAS100CS-AU_R1_000A1?
Booster IC: XL6008E1

At the moment I don't know how high I can push LEDs and still maintain reasonably low temps (45x75mm matrix size, passive cooling, 100*100mm aluminum PCB). To limit and balance current I will be using 64R 1% resistor for 20mA(180mA total) and two in parallel for 40mA(360mA total) – I assume setup like this will balance current between 9 lanes well enough? Matrix needs to be turn on/off, so to save extra BOM I designed matrix to be off with 12-24V input (way below 37.5V(2.5*15) forward voltage). Input and output will have few 10uF caps (double them up for output to use 50V rated caps).


Also 3.3v <100mA is needed from the same 12-24V input voltage (different double sided PCB). I assume I can just reuse same diode even tho it will be way ovekill, but how about inductor? What value should I use to get stable output for MCU and other logic ICs?
Regulator IC: ME3116AM6G


P.S. this will end up as an open source project...

Benta:
A very general comment:
you seem to presume that all LEDs have the same forward voltage. Are they selected for this?
If not, I'd recommend active current control per LED string.
Like this:

mariush:
I'd encourage you design it as a step-down / buck driver or as a linear driver.

Your leds have forward voltage of 3.3v typical, up to 3.6v .. so let's say you design this to use a regular laptop adapter (18v...20v - and 24v would also work but less efficient) then you could have chains of 5 leds to form chains giving you 3.3v x 5v = 16.5v leaving 1.5v+ available for the led driver.

So each of your columns could be either 3 channels on a led driver, or you could parallel the 3 chains of 5 leds to a channel.

with chains of 5 leds, and 20-60 mA per led, you're looking at 27 groups of 5 leds so 27x 20 - 60 = 540mA - 1620 mA  (a 18..20v 3A lcd monitor/ laptop charger would be perfectly fine for this)

You have led drivers like AL8843 which can do up to 3A of current and allow you to set the max current through one resistor, and then use either a potentiometer to adjust brightness, or a pwm signal from your microcontroller
AL8843 :  https://www.digikey.com/en/products/detail/diodes-incorporated/AL8843QSP-13/10668306

another similar driver : https://www.digikey.com/en/products/detail/diodes-incorporated/PAM2863ECR/4033265

3dgeo:

--- Quote from: Benta on June 27, 2022, 07:04:48 pm ---A very general comment:
you seem to presume that all LEDs have the same forward voltage. Are they selected for this?
If not, I'd recommend active current control per LED string.
Like this:

--- End quote ---

Well, as LEDs will be from a same reel I assume that differences between 9 lanes with 15LEDs in series shouldn't be big issue... ?
My design is a constant current as booster IC vref is 1.25V and 62R will give 20mA@1.25V per lane. Tho I'm not sure about other lanes...
Your suggestion seems a bit too BOM/PNP intensive, if lane balancing will be an issue I think I'll go with CC LED driver on a low side.



--- Quote from: mariush on June 27, 2022, 07:54:05 pm ---I'd encourage you design it as a step-down / buck driver or as a linear driver.

Your leds have forward voltage of 3.3v typical, up to 3.6v .. so let's say you design this to use a regular laptop adapter (18v...20v - and 24v would also work but less efficient)...

--- End quote ---

You probably missed that input is 12V to 24V. Even if input range would be 18-20V I'm also having hard time understanding – I assume you suggesting paralleling  27 lanes of 5 LEDs, but in that case there is still a lane balancing issue, and in your case this may be *3 more problematic as there would be *3 more parallel lanes and *3 current.

I was considering 16lane LED drivers, but due to dynamic input voltage they are not best choice in this case in my opinion.



Any feedback on inductor or diode?

viperidae:
As long as an led doesn't fail short circuit in one of the unmonitored strings. That would cause excessive current in the remainder of the string.
An open circuit failure in the current monitored string would cause excessive voltage output of the boost regulator, since the top of its feedback circuit will be open.

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