Damn it, Dave! You made me finally decide to upgrade my lab PSU that I built in the early eighties! Especially now, that my time is very, very limited...
It is a 350W linear PSU (0.0-32.0V/0.00-10.00A) based on the legendary LM723, whose circuit I redesigned from scratch a couple of years after its initial construction, and it still goes strong with few recent minor losses (the 20 years old output filtering capacitors!) after having it used to debug crude switching power supplies! All these years it did never complain, even when I used it to be charging my motorcycle and car batteries!
Thanks to you, the LT3080 got my attention and I found it to be an excellent voltage follower for the upgrade of my lab PSU, even though I might need to change the power stages (2 x 2N3772) with faster ones. I initially intended to add a few exotic features like, a deep memory to be storing real time the output voltage and current history and to display or send the data to a graphics display or over a serial line, and a few hundred steps of arbitrary output waveform programmability. Now, I think that adding a switching tracking pre-regulator stage would not be that irrational...
Anyway, I have made a few drafts that simulate perfectly well, in a hope that you will find them useful for the PSU you are constructing. I am using the AD8628, this lovely Analog Devices's chopper, that does not only have one of the best offset values in the market but it also needs only a few micoseconds time to recover from an I/O saturation or overload condition, instead of the usual 50ms most choppers need. There is also the AD8616, if you need any faster solutions.
Linear PSU v1
This, above, was my first attempt. Kelvin connections for the I/V sense resistors and dividers. R4 adds to the output voltage the shunt resistor voltage drop (= <Vout-> * R2/R4), while V_Set has a gain of R2/R3; R1 balances the overall gain of U1, adding to the output an amount of 0V * R2/R1. My initial thought was to keep my current shunt configuration as it was (low-side current sensing), but I ditched that idea because this way I insert extra stages to the regulation loop, compromising LT3080's accuracy and speed. Next, I used a current-sense IC but the overall stability is not of the standard I expect it to have. But the voltage regulation loop seems to be flawless:
Linear PSU v2
This is only a draft, but the solution you might be seeking for your PSU is the U3 stage, above: Personally, I need 5.0V for the 16-bit, <1 LSB INL ADCs/DACs and, possibly, for the graphics LCD; otherwise, everything can run on 3.3V. Vcc can be anywhere between 3.3-5.0V while Vee=0.0V. If you are paranoid about the ground level accuracy, set Vcc=3.3V and Vee=-1.0V and you are done! You can use any low voltage op-amp to drive the LT3080 voltage follower by using an extra high voltage (>40V) MOSFET with an Rds of 100 milliohm or better: See the U3 stage. Additionally, if your LT3080 drives a power stage instead of the load directly, R8 shuts the power stage off, providing the first milliampers to the load by the LT3080 itself and after that the power stage takes over; R9 ensures that the LT3080 will never provide more than 40mA, keeping it always cool on the PCB -no need to mount it in the hot heat-sink and have its characteristics drift off.
I hope that the above could be of some help; of course, any ideas are welcome!
-George