LED array design gone wrong ?

[Sarvesaa]

Hi guys,

I designed a LED array PCB and got them fabricated from JLCPCB. The array also consists horticulture LEDs from Wurth Elektroniks.

The array consists of 10 of white LEDs with a forward voltage of 34V, all 10 in series. The total forward voltage is 340V, at that moment I thought I could design a boost converter later to drive them, but now it seems it is not the right decision. I was able to drive them with LED driver from my aquarium light's LED driver which gave a output voltage of 310V. It is capable of turning on the light but the intensity is obviously low. The horticulture LEDs work as intended.

I am wanting for a brightness control of the 340V LED array, please give ideas for it.

I have attached the PCB design below and the datasheets. Please give your thought on this project of mine.

https://evelta.com/content/datasheets/012-67-22ST-KKE-E40130380U2-SZM-2T.pdf

Thanks

Sarvesh

[Ian.M]

You've got less than 1 mm creepage or clearance distance to ground for a track with 340V DC on it and possibility of condensation.    There's no saving this design short of potting the LED array in clear epoxy!

You could possibly rework the board to fit much lower Vf white LEDs to get the string voltage under 40V so you could use a similar driver to that for the horticulture LEDs.

[rteodor]

I am wanting for a brightness control of the 340V LED array, please give ideas for it.

HV9961
LED Driver with Average-Current Mode Constant-Current Control
Linear Dimming Input
PWM Dimming Input
Input DC Supply Voltage Range 8-450V

Has some cutoff at the lower end of the dimming range (I think for under ~10%) but plants would not complain.

If the PCB holds the voltage as Ian.M said above....

[oldrev]

https://www.eevblog.com/forum/projects/diy-open-source-aquarium-led-controller/


You're welcome.

[neillnz]

Following on from Ian.M's comments about the narrow slot between the high Voltage and earth I am wondering why the board even has a copper flood/pour earth plane? 

I think a better approach would be to redesign the board as follows:

1. Remove the earth plane.
2. If your PCB is regular FR4/fibreglass and not specifically a thermal material i.e. aluminium then make the pads for the LEDs much larger to help dissipate heat from the LEDs.  The data shows that LEDs are around 0.85 W each so I am surprised they do not show a better mountng method i.e. much larger pads. 

It's a pity those LEDs have such a high forward Voltage.  It would be so much easier to drive 10 1W LEDs at 350mA with a forward Voltage of around 3.0V each as there are many driver options available.

[tooki]

Hi guys,

I designed a LED array PCB and got them fabricated from JLCPCB. The array also consists horticulture LEDs from Wurth Elektroniks.

The array consists of 10 of white LEDs with a forward voltage of 34V, all 10 in series. The total forward voltage is 340V, at that moment I thought I could design a boost converter later to drive them, but now it seems it is not the right decision. I was able to drive them with LED driver from my aquarium light's LED driver which gave an output voltage of 310V. It is capable of turning on the light but the intensity is obviously low. The horticulture LEDs work as intended.

I am wanting for a brightness control of the 340V LED array, please give ideas for it.

I have attached the PCB design below and the datasheets. Please give your thought on this project of mine.
…

Don’t even think of using screws in the two holes that are between the hyper red LED traces unless you use plastic washers. Screwing down the screws could easily break through the solder mask, shorting the trace to ground.

When you make mounting screw holes, always, always, always do one of the following:
1. Make a circular pad large enough to fully enclose any metal hardware you may use. Depending on the situation, you may connect that pad to ground, or leave it floating. For M3 screws, I usually use 8mm diameter, so that there is room not only for a standard 5.5mm nut or standoff, but also for a washer, as well as for the nut driver itself. This is what I almost always use.
2. Create a circular keepout around the hole, so there is no copper of any kind underneath the mounting hardware. Diameters as in #1.


I will also note that there was absolutely no reason to have the trace hugging the holes like that. You could have easily just moved the entire trace down by a few mm to give the holes a wide berth.

The trace connecting LED1 to LED6 is also perilously close to the rightmost three mounting holes. Use plastic washers here, too.

[oldrev]

I didn't look closely when I replied earlier. As someone who has been playing with LED aquarium lights for many years, this PCB design has several fatal flaws:

* I'm guessing these are 3535 LEDs, which means their power is likely between 3W and 5W. Take a close look at the wiring of your LED pins. Notice how the tracks suddenly become thinner where they connect to the LED.

* Aluminum PCBs cannot be soldered with a soldering iron, So the thermal solder pads won't work. You need SMD sockets.

* Aluminum PCBs cannot have plated through-holes, they can only have screw holes. And a keepout area is needed to isolate it.

* 340V voltage used on top of a fish tank? No thanks.

[amaschas]

Why the LEDs all in series? You could have a parallel/series arrangement and use a much lower voltage.