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Jiggerypook:
I have some newbie questions if anyone is willing to answer. I have modified a schematic that I assume was created by Kleinstein and through testing in ltSpice have somehow made it seemingly stable. I have attached a screen shot of what is puzzling me. I copied this test from another post on this forum.

1. What am I looking at? Frequency response or phase relationship or neither?
2. What does it indicate about the circuit? Is it a good result or do I start over?
3. Is there a better test to indicate whether this circuit could be stable under different load conditions?

I would like to build this power supply but am struggling to understand all of the stability issues that may apply. I have read up on bode plots and trying to understand poles and zeros but I'm not there yet. I'm sure that it has to do with leading and lagging voltage and current relationships but then again I could be wrong. I am trying to learn. As far as my understanding goes this test may be meaningless for what I am trying to do.

Please help.

p.s. I don't know how to resize so I hope this is ok.
iMo:
The PSUs could be analyzed for the stability, with a phase margin output (and gain).

There is a tech-article from ADI(LT) I've been using.

https://www.analog.com/en/technical-articles/ltspice-extracting-switch-mode-power-supply-loop-gain-in-simulation-and-why-you-usually-don-t-need.html

Jiggerypook:
Thanks IMO, I will read that. It never came up in any of my searches. I just hope that i'm not too thick. lol
Jiggerypook:

--- Quote from: imo on May 27, 2019, 12:07:02 pm ---The PSUs could be analyzed for the stability, with a phase margin output (and gain).

There is a tech-article from ADI(LT) I've been using.

https://www.analog.com/en/technical-articles/ltspice-extracting-switch-mode-power-supply-loop-gain-in-simulation-and-why-you-usually-don-t-need.html
[/quote
I couldn't seem to co-relate a switcher to a linear but this was somewhat helpful.

I assume that the feedback loop in a linear supply would be the error amps. My experience with this circuit was that the current limit was the cause of the oscillations, therefore I attempted to add positive feedback to create some hysteresis as I had seen in one of Dave's videos. This had a secondary effect that allowed me to bring the CV/CC threshold more closely together, improving accuracy.

So, does this mean that I need to inject the test signal into the inverting pin of the current limit op? If so, between C9 and the inverting pin or between R26 and the inverting pin?
Do I just probe the output or output/input?

 

Sorry for all of the newb questions, I'm also just learning ltSpice.



Thanks again for any help, I am trying to learn but right now it's a steep grade and I want to build a stable power supply to further my understanding of electronics.

--- End quote ---
Jiggerypook:
OK, I read the article that IMO referred me to and attempted to apply it to a linear supply but quite obviously I have no clue. I am a total beginner and have little understanding of how to address the stability issues of a linear power supply except to zero in on the problem area and use trial and error methods to achieve stability, as I have done so far.

So, thanks again IMO.
Here are my strange results:
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