/diy/ - Do It Yourself

Trying to design babby's first switching benchtop power supply, of the non-isolated buck topology, preferably with a current and voltage knob that works just like those LM2596 modules. I'm trying to design it discretely from op-amps and comparators and the like but I can't seem to get the variable duty-cycle sorted at all. Do I need an instrumentation amplifier? I'm guessing rail-to-rails help, but is there an easy way to not require them? In general, I'm asking for pointers to circuits or sites. Perhaps looking at a buck converter IC's datasheet for the equivalent circuit would give me something usable, but I suspect they'll be a little complex. Pic related.