[No TL;DR provided]
I am an undergraduate electronics engineering student and I am working on designing a linear bench top power supply with foldback current limiting. Inspired by designs all over the internet (30V-3A types mostly) I've already came up with a complete design and with the help of LTspice I have resolved most of the oscillation issues (to the extent I am concerned, of course).
For voltage and current adjustment, I have used a zener regulator with an opamp to obtain various reference voltages and I observed that the input power supply ripples and transients are affecting my reference voltages which causes oscillation.
My solution was to change the zener configuration, as I've seen the issue with a trivial design. Since my whole design is irrelevant, I'm posting the zener voltage regulator part:
Trivial design was #3. Suffering from supply ripple, changed to #4 but than realized that better(?) alternatives are #1 and #2. They turned out to be great.
I know why #1 and #2 are superior to #3 and #4, basically power supply rejection . Simulations also verified this. Small signal analysis on ripple source with only gain plots (ngspice) are as shown below:
It is obvious that #1 and #2 are doing great, but my first question is, which is better? Is there any aspect of why one should be preferred over the other?
And my second question: Is it possible to make design #4 perform better by playing with capacitor-resistor values while still having a reasonable settling time?
Thanks in advance.