I've tossed around the idea of a UV LED exposure unit, but instead of using a dedicated constant current IC I was thinking about using voltage regulators set with resistors in series followed by the LED strings. Either an LM317 or a 78xx regulator, I just have to make sure the supply voltage is greater than the forward voltage of the LED strings plus the drop across the voltage-regulator/resistor.
My first exposure unit was just a wooden box with a compact fluorescent bulb in the bottom(consumed 25W, was said to output 150W equivalent light). The exposure unit worked rather well, but took 8 minutes for an exposure with positive pre-sensitized PCB's. The max exposure area was 4" by 6" (which is the largest sized PCB I plan to make).
UV LED's would reduce the exposure time significantly and if properly spaced and height set right, would give reasonably uniform coverage. I'm thinking about building a double sided exposure unit when I move to the UV LED's(but thats down the road).
Something that has got me thinking: "Why haven't we seen any table top UV LED exposure units on the market yet?" All I've been able to find are UV fluorescent models, and the majority are all out of my price range.
Anyways, good luck with your exposure unit.
--- In Homebrew_PCBs@yahoogroups.com, "javaguy11111" <javaguy11111@...> wrote:
>
> After about a years delay I am back to working on my UV LED exposure box.
> I finally got my LED panels soldered and was getting ready to order parts for the power supply.
>
> Not really looking forward to building that board, I decided to do a quick check on constant current sources. Generally they are very expensive, but a quick search on Mouser showed that there is now a 20ma constant current source meant for LEDs that cost 44 cents each. The part number is CL2N3-G from a company called Supertex. Note that this 20ma is also the nominal current needed by the UV LED's from Best Hong Kong, which I think several people have ordered.
>
> I have some on order and should get them in a few days. I will do an update post on how well they work. However I figured I would mention it now in case someone else was working on a box and considering designing a power supply or using current limiting resistors. I think these constant current sources will work much better.
>
> Also for the LED panels used stripboard/vero board from All Electronics.
> For me, I organized as 11 rows with 7 LEDs each.That gives me a board big enough to adequately cover the largest board I built so far.
>