I've needed more than 2/3 PSU channels for a while, so I made a L200 circuit from the datasheet. It's w/ a uA741 that should be providing a voltage to the L200, based on the L200 OP current.
https://www.ges.cz/sheets/l/l200.pdfThe 741, if I understand the circuit, should try it's best to make Vn=Vp , and so it's OP will move a few volts, from Vp as needed. And the L200 is looking at the difference between is own OP voltage, and the OP from the 741......and comparing that to a ref of Vsc=0.45V. The math seems to work, and I can get LTspice to do about the same (w/ more op-amps/BJT as a basic model of a L200).
But when it's wired up, the 741 is basically just acting as a buffer, turning the 100k pot, only moves it's OP by 2-3mV, and so the difference voltage to L200 is way off the Vsc=0.45V threshold.
And so the L200 does not cut back it's OP V or I
So I unhooked the 741's OP, and applied my own voltage to the L200's Ilim, and it works. But the 741 still acts like a buffer, just matching to within a few mV of the load voltage, regardless of the 100k pot setting.
I swapped in a new 741 and cleaned it and checked all the rest, same thing.
In the middle picture, I would say the op-amp output should be
Vo = Vp - (Rf/Rn)*Rsc*Ilload