This morning I finished my first real complete build of the "EEVBlog" constant current sink. It's more or less built on Dave's design. I used an extra op-amp on the LM324 as a comparator to sense load and drive a an LED when current is being drawn. I figured that might be useful if the panel meter failed or a short reared it's ugly head.
I hand-soldered all the traces on a project board and built the whole thing up in an old ATX power supply box. I used the 80mm fan in the box to cool the MOSFET and load resistors. The heat sink that I used is farily small, but it didn't get too hot during tests with the fan running. The whole thing runs on a 12V wall wart, with a 7805 providing power for the panel meter.
The device will draw well over 2 amps, but the panel meter is 2000 count, so I'm effectively limited there. Other than that, it's just a 10-turn pot, a switch to turn it on, and a switch to connect and disconnect the load. In the earliest breadboard versions, I had a run-away scenario with I turned off the sink with the loaded power supply still attached, so I thought that a switch would be prudent.
I'm been fooling around with this stuff for a while, but this is my first real project like this. I'm sure that I could have done a number of things better, but I'm pretty happy that it worked and no magic blue smoke escaped. Definately going to etch a board for the next circuit this complicated.
Thanks to the folks who commented on my other thread when I was having trouble on the breadboard test phases. Couldn't have gotten this done without those hints!
Pics attached, yes, I do have to redo the paint job
. I was too impatient to let it cure properly before assembly.