Right, I have found some time to get this project going. Some of you may be aware of the design / review phase that I went through here:
https://www.eevblog.com/forum/index.php?topic=4685.0Some people have expressed interest in seeing the progress of the project, so here we go. Some of the pictures are appalling because I couldn't be bothered with my SLR tonight, I just used a P&S camera, so I apologise.
So my order comprising of the rest of the components arrived very promptly the other day from Mouser and I could make a start.
Although this project is supposed to functional, it is also a prototype, so I have built the current source on veroboard. It is quite well populated though, so I am pleased with it.
The board is not quite complete, it needs a few more wires, the MOSFETS and decoupling capacitors.
Due to the very high forward voltage (as far as LED's go) of these particular LED's, it was not feasible to wire them all in series and drive the the string that way. The voltage drop across the string would then be over 400V - ja, not so cool. So I have opted to drive each LED via it own "channel". I have also included "soft start" to minimise the effects of inrush currents and it's kind of cool too
The circuit takes about 1-2 seconds to supply the full 270mA to the lamps.
So here is the board.
Next, we move on to the case. It has a standard IEC inlet, circuit breaker and 120VA transformer. The two 10 way JAE connectors go out to each of the bars of five LED's.
Now, the heatsinks did cause some issues. The main issue being the price. Some of the heatsinks designed for this type of LED were almost twice the price of the LED's themselves! Sensibly priced heatsinks were either obsolete or out of stock. I settled on these Wakefield heastsinks which are designed for star LED's, so these don't fit quite as easily, but the price was more agreeable. They are rated at 1.55C/W.
I have not quite decided how to mount the LED to the heatsink yet. I am either going to bolt them on with long bolts and nuts or glue them on with Arctic Silver thermal adhesive. That comes at a later stage, so I have some time to think.
At the moment it's just stuck on with sticky backed thermal pad.
I have operated the lamp at 270mA for an hour on this heatsink and it gets up to about 50 degrees C. 270mA (11 Watts) will output ~900 Lumens on this particular LED - which is very bright, it's overloaded the camera lol.
Although it looks like the LED lamp is the only light source switched on, it's not. It's just the brightness of the LED that forces the camera to adjust, so everything else looks dark.