Since I have a bunch of transformers and a box full of 2N3055, I decided to build a linear lab power supply. Since I'm quite bad at linear circuits, I studied a few schematics until I came up with something that's close to what I want.
Below is the simulation of the main circuit. The main pass transistor is biased by Q1, and U1 and U3 are used for voltage and current feedback. V2 will actually be a TL431 5V reference and a potentiometer, while V3 will be taken from the reference, also adjustable with a potentiometer.
First, I would like to understand how Q3 and Q4 work in that configuration, it seems very strange that they're in series.
Another issue is with adding U2 into the schematic, which makes the output of the PSU unstable. It is used as a gain of 4 amplifier so that lower value current sense resistors can be used, and without it the output is stable. I suspect is some compensation issue, so I'd like to know how to solve it.
The final circuit will also have a tracking pre-regulator based on LM2576, but I couldn't find a way to simulate it.