My version of the ubiquitous Electronic Constant Current Sink - Page 1
Forum section: electronics / projects

author: Jimmy the Squid
author_rank: Regular Contributor
timestamp: November 04, 2012, 06:52:20 pm
content: 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.

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: November 04, 2012, 10:46:03 pm
content: Looks good to me ...Awesome job

author: Fluxed Matter
author_rank: Regular Contributor
timestamp: November 05, 2012, 03:26:43 am
content: Looks great! Awesome job!! I wish I could get mine to work.

author: McMonster
author_rank: Frequent Contributor
timestamp: November 05, 2012, 06:22:34 am
content: Looks nice and clean. DO you have any tips about making solder traces on the perfboard? I always end up with a totall mess and lots of jumper wires, even though I try to use bent or cut off leads as much as possible to form the traces.

author: krivx
author_rank: Frequent Contributor
timestamp: November 05, 2012, 01:43:13 pm
content: I use a roll of uninsulated solid wire to layout perfboard tracks. It's the same as using resistor legs except that you can make them the exact length that you need.

author: Jimmy the Squid
author_rank: Regular Contributor
timestamp: November 05, 2012, 03:44:29 pm
content: Quote from: McMonster on November 05, 2012, 06:22:34 amI watched a video somewhere that showed the general technique. I would post it, but I can't find it again. I use a chisel tip just wide enough to be able to touch the edges of two pads. Essentially, you go through and place a dab of solder on each hole in the track, the come back through and solder every other pair. It looks like . . . . . . then _ . _ . _ . Then you start back at the beginning and fill in every other gap, then start at the beginning again and fill in the rest of the gaps. The key seems to be to start with both soldered areas are relatively cool. If one is hotter (like you just soldered it) it will want to suck up all the new solder you add, and you get a huge blob.Doing all that close-in work around the 14 pin DIP was very difficult, and patience is required in abundance. One wrong move and you can break the trace next to the new one you are putting in. The solder traces worked great for me on 555 timer circuits, but I think I'll try etching for the more complicated stuff...

author: grenert
author_rank: Frequent Contributor
timestamp: November 06, 2012, 04:47:24 am
content: Looks nice! I have no mechanical aptitude so I would be very pleased to have done that paint jobSince your meter only goes up to 2A, it might be a good idea to scale the range of the adjustment pot so that it maxes out at 2A. If you go over, you won't know how far over. Best to not let that situation arise!

author: Jimmy the Squid
author_rank: Regular Contributor
timestamp: November 06, 2012, 02:25:51 pm
content: Quote from: grenert on November 06, 2012, 04:47:24 amThat's good advice, thank you. My original plan was to have a triple throw switch in the circuit that switched in different resistors on the positive side of the potentiometer to create current ranges. I might just resurrect that idea and make it max out at 2A. Better safe than sorry.

author: T4P
author_rank: Super Contributor
timestamp: November 06, 2012, 03:33:08 pm
content: Solder tracing or jumper-festI use jumper-fest because i'm not going to use up all my solder in a few projects