This article describes a simple 3-transistor voltage regulator with current limiting. It is based on a conventional design of unknown origin. The component values quoted below were chosen to provide a stabilised 12V 40mA output from a 17V DC supply; but I show how they can be calculated for a customised output.
Doesn't C degrade the transient response? Won't it have poor load and line regulation? If the zener was in line with the base instead of the emitter, its current wouldn't change quite as much due to change of input voltage
Not sure about that. For circuit simplicity some zener current change is inevitable wherever the zener is placed. If the zener were in line with the base then the current through it would be very small and its knee voltage would be less well defined (leading to poor regulation, hence current change) than with the zener in the emitter line. So its swings and roundabouts.
I want to make a circuit, using a 3,7v input, output variable 3v to 6v, with 1,5 to 2,5 amps. It must be small, like 2cm by 3cm max. Does this sound possible with the circuit you've designed, obviously using the necessary values?