Driver for 3W Leds - Page 1
Forum section: electronics / projects

author: illusive
author_rank: Regular Contributor
timestamp: March 15, 2017, 09:15:36 am
content: Hi all,I'm building myself UV LED lightbox for PCB exposure. I got 9 3W LEDs off ebay (3.5V and i will drive them with about 500mA) and i need them to be at about the same brightness i.e. same current through all of them. I have an 19V laptop power supply and the best way maybe will be to put them all in series (~31.5V), so stepping up the voltage is needed, then current limiting.Is there anything raeady to use? Through hole package is prefered.

author: sleemanj
author_rank: Super Contributor
timestamp: March 15, 2017, 09:29:49 am
content: I would drive them at ~1W, 300-350mA, it will be more than sufficient and better for the life of (unknown quality chinese) leds.To give an idea, I have a box that uses 8 1W UV leds covering over an A4 page size area, through 2 diffuser layers, and it takes 2m40s to expose dry film resist. So yeah, 9W of UV leds is plenty for most purposes I think.There are plenty of buck or boost mode LED drivers on eBay/Aliexpress, usually they come in 1-3 LED Buck mode, or 4-7 LED Boost mode, both of these driver styles will typically take about 12v to 20v input.

author: illusive
author_rank: Regular Contributor
timestamp: March 15, 2017, 11:27:32 am
content: Thanks for the advice. Is the diffuser mandatory or you just wanted the leds close to the board?I've found some nice boost drivers on ebay, but most of them are with fixed output current.First i was thinking about boosting the voltage with mc34063 and then cc driving with lm317. But this method is too much hassle so i'm trying to find a IC build for this.

author: sleemanj
author_rank: Super Contributor
timestamp: March 15, 2017, 12:39:18 pm
content: Quote from: illusive on March 15, 2017, 11:27:32 amDue to the large area to cover (wide equidistant spacing) and relatively narrow beam of leds (even wide angle ones) I found diffusion necessary to get an even coverage without (to the eye) hot spots. Naturally this will have an effect on attainable resolution, but i can't say it has caused a problem for me really, i can go to 8/8mil if necessary, although usually stick to about 12/12 if possible.My diffusers on that box are just made from a sheet of glass with a thin diffuse plastic cutting mat from a dollar type store stuck on each side, mounted half way between leds and the target.

author: crazyguy
author_rank: Regular Contributor
timestamp: March 15, 2017, 04:02:18 pm
content: Quote from: illusive on March 15, 2017, 11:27:32 ambuy a DC-DC Boost Converter Module with Constant Current Control, set the output to 35V / 500mA or whatever LED current you wantdon't use LM317 analog regulator for current limit, not energy efficient, 9pcs of 3W LED already very hotMingHe D3806If you don't need 500mA output, You may use AMC7135 LED driver chip

author: Zero999
author_rank: Super Contributor
timestamp: March 16, 2017, 08:21:05 pm
content: Quote from: crazyguy on March 15, 2017, 04:02:18 pmBear in mind that it's still a linear regulator so will only save power if the output voltage is close to the input.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 17, 2017, 05:48:34 pm
content: Slightly OT, but I recommend (from experience) using one single higher power LED unit further away instead of a diffuse box. Point light source gives you quite a bit of leeway against error introduced by distance between the ink traces and the board, which happens if you don't have vacuum table, or if you accidentally forget to mirror the mask image before printing.We use 20W Ebay UV LED about 30-40 cm away from the board area - even though we have a vacuum system. This was done as a response to the resolution problems, causing failures with 8mil/8mil traces, on the old diffuse exposure system (UV box).