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I’m designing SLA 3D printer and I need to design UV LED array for LCD screen backlight. Preliminary design is 5x3 (5 parallel lines with three LEDs in each). All LEDs will be soldered on PCB.

The catch is that every LED will have 1W and my inner engineer cries out for active regulation, even though I understand, that passive regulation (via resistors) would be much simpler. I’m just high school student with very little knowledge about electronics, so could you point me to some solutions?

I’m going to solder the PCB myself and I’m not working on the project full-time, so I would definitely prefer something simpler (maybe regulation via MOSFETs?). I don’t need complicated dimming of individual LEDs via IC in BGA package or something like that.

LED parameters: voltage: 3.2-3.6V current: 300-350 mA further info: https://www.aliexpress.com/item/1W-3W-5W-Warm-White-Royal-Blue-Orange-UV-Violet-RGB-High-Power-LED-Chip-Light/32804097246.html

I’m sorry for any grammar mistakes, I’m not a native speaker.

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  • \$\begingroup\$ What kind of power source will you use with the LEDs? How big is this screen? 15W of LEDs sounds like a lot of light. \$\endgroup\$ – Elliot Alderson Aug 6 '18 at 14:21
  • \$\begingroup\$ You aren't going to print much with a 5x3 resolution. \$\endgroup\$ – Trotski94 Aug 6 '18 at 15:03
  • \$\begingroup\$ Heh. It's not every day you hear about a LCD screen working in UV. \$\endgroup\$ – user253751 Aug 7 '18 at 0:57
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I'm guessing the application you intend is to use UV curing resins by mounting a powerful UV source behind a diffuser lens and LCD screen as a light blocker. The LCD is kept just above the surface of the resin as the tank is filled and the LCD rather than the UV LEDs provides the image resolution. If this is the case, the LEDs can all be the same brightness, which is an advantage because you can use different voltages, 54V for all 15 LEDs in series, 18V for 3 strings of 5 LEDs, 10.8v for 5 strings of 3.

It's a benchtop device so you can get away with things being a bit bulkier, which will make things easier for you.

Cooling the LEDs is important, so you may want to look around the usual DIY sources for some massive aluminum heatsink or a bunch of smaller ones depending on how far apart the LEDs are. The MCPCB stars that most power LEDs come mounted to are actually usually adequate for low power, especially with current control, but if you're going to have 15W together in an enclosed space beside an LCD you don't want to heat up, it wouldn't hurt at all to keep it cooler. This will also help avoid a long heat up time while you wait for the LEDs to reach thermal equilibrium and for their brightness to steady. LED efficiency also improves if you keep them cooler.

As for a driver, because it's a desktop unit you can get yourself a constant current LED driver of appropriate voltage range for the series/parallel arrangement you decide to use. They're usually about 4-5 inches by 2 inches by 1 inch or smaller depending on power rating. 120 or 240V goes in, constant current comes out to drive the LEDs. If you choose one that's dimmable you'll be able to adjust brightness if you want.

Here's a link to the section on DigiKey. You can find this sort of thing at numerous websites and sometimes even hardware stores, so you can use this to get an idea what you're looking for. Just fill out columns with things you do know, one at a time, and use "apply filters" in between until you narrow it down. Constant current is usually used with LEDs to eliminate thermal runaway without using series resistors.

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  • \$\begingroup\$ Thanks for long and insightful comment :). I'm a bit concerned about mounting the LEDs on the heatsink. I'll get the PCB version, but there aren't any mounting holes, so the thermal compound would also have to be a good adhesive. More elegant (and more time-consuming, I know) solution would be to order just the LEDs without PCB and create custom PCB. This would also allow for active regulation of individual strings (with something like LM334). The real question is, is it overengineered solution? \$\endgroup\$ – adam440 Aug 7 '18 at 10:56
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A single 300ma constant current module ought to do it. I think the 17w units are 50v and have the right voltage for 15 of those LEDs in series.

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