/diy/ - Do It Yourself

>>2556512
>inverted signal goes to V+ so it is stable
mind boggling but makes perfect sense.
i always thought that negative feedback goes to V- and positive feedback goes to V+.
wrong assumption.

>common-emitter circuits are a lot less stable than common-collector
Yeah I believe some LDOs use common emitter for a lower dropout. I played with RC in the feedback before to prevent oscillations.

>The diode is just there to drop some voltage
My simulation doesn't work without the diode at all. It outputs -12v (negative rail) instead of -3v as set by by Vref.
And it is funny that even the simulation is oscillating without the cap and a resistor in the feedback path to slow it down. But dropout is super low, so it is worth messing with. In fact in my simulation it goes almost all the way down to -12V rail since there is no p-n voltage drop in the path. No need to bother with FETs! But perhaps it is too good to be true in practice.