Some random thoughts:
I have made 3 different versions of bench PSUs, both working on my desk, except the very first ones whose diodes melted everything around them. They are 0-30V/5A with 2 channels each (total 4 channels).
The second version uses pairs of LM2679s (5A) to produce 3-6V over the required voltage and then followed by a linear regulator using two FETs to determine current limiting and voltage (one for each). Because of the LM2679s it runs very cool.
I also have one wire (should have two) running all the way to the load to sense the voltage so that it stays good under large currents. The wire is soldered on the same crocodile clip as the power output so it is not messy at all.
The linear version produces very clean output especially at high currents (all the way over 5A) whereas the LM2679 introduces some noise spikes.
I was kind of forced to go with 20V 3A output mainly because of budget constraints. I've done the math and had to stick with a rather cheap (don't read crap quality) and readily available 24V 100VA transformer. The higher voltage transformers (would need a 36V one for 30V output) were significantly more expensive for the same VA rating. On the other hand, I still have two transformers taken out of an old Epson printer, one is about 30V @ 1A min, the other one about 10V @ 2A and I will use them for a second lab PSU. For this one however, the higher output current was more important.
I was thinking about the feedback wires being separate to counter the voltage drop from the regulator output to the output plugs. PCB layout should be carefully done to avoid ground loops and other nasty stuff, especially since this design will probably use about half a dozen boards, the reason being my current lack of gear to make PCBs larger than about 5cm by 10cm at home, currently single layer only, and it's too expensive to have them made elsewhere (even locally) in one-off quantities.
As for the switching noise and the ripple rejection (the LM2596 runs at ~150kHz), I'll go brute force and use LC filters at the input of the linear regulator. It was cheaper for me to use a smaller heatsink and a switchmode pre-regulator than have to get rid of 60+ watts of heat.
x2 I would love a full set of schematics. Seems like a fun project, and I could definitely use a bench PSU! I have some stuff laying around as well...
I'll have to warn you though, if you want to build everything yourself, especially the digital control part, you'll need a bit of experience to get everything right.
The analog part, however, is pretty simple and it can work with analog controls (pots) and that was the initial idea, but then it all went south...
As for the fun part, every project attempted with a certain level of complexity will have its ups and downs.
To get an idea you could look at Ian Johnston's design, from which mine borrowed a few ideas
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
. Also, since I haven't prototyped anything yet, none of the schematics posted so far are guaranteed to work perfectly or even work at all without some small tweaks (no matter how well you do the math, real world physics can and somethimes will always be one step ahead of you).
![Sad :(](https://www.eevblog.com/forum/Smileys/default/sad.gif)