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Salas 19th May 2018 08:48 PM

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Originally Posted by selfy (
Salas, where/how do you “break” the closed loop to simulate the open loop?

Like this:

jackinnj 19th May 2018 08:53 PM

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Since layout is critical when designing for line regulation, will have some boards made as close as possible resembling those illustrated in the first few pages of this thread.

I compared three versions of the design, one dating from 2011, the other the V1.2R 22V, the last the schematic illustrated at the beginning of this thread. The PSRR of each vary in significant degree.

The 2011 version measured 131dB when tested, or about 10dB worse than the simulation. The Salas was a real champ when it came to PSRR in the Linear Audio bake-off.

Salas 19th May 2018 09:09 PM

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Yep, it was quite interesting how close your lab findings followed the simulation trends back then. This year's PSRR simulates like attached. The flat trend in audio frequencies is there, your attempt looks flat even in higher frequencies, about numbers I don't know what may be seen in the lab with real parts and boards practice. I will ask Tea-Bag to send you an original board on my expenses. Thanks for your contributions in measuring and for your interest.

arpagon 19th May 2018 09:14 PM

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Originally Posted by Salas (
Like this:

It's just not correct.
I think it should be this way.

Salas 19th May 2018 09:28 PM

It is evidently correct. Same method on the 2011 one that Jack measured close to sims in all areas. Also, according to your analysis my prototype would have behaved more or less like Selfy's when tested with his same load parts but it didn't (posts #54-59).
Different methods different parts different models differentiated circuit sections. We will not have a chance to match those analysis.

Salas 19th May 2018 09:35 PM


Plotting Loop Gain Using the Tian Method - Spring 2011

arpagon 19th May 2018 10:07 PM

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Originally Posted by Salas (

Thank you for pointing me out this great material but I think I passed the lesson about Tian's probe a long time ago.
What about your decision to insert the probe - I do believe it is wrong. Just imagine where the NFB comes from and where it goes for. Of course there mustn't be any parallel loops.
And if my initial drawing seems a little bit controversial to you, here's another one which will probably be more convenient.
Of course results are the same.

Salas 19th May 2018 10:32 PM

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Its after the CCS between the shunt voltage part and the shunt current part again

arpagon 19th May 2018 10:45 PM

Yes, I saw this but I'm stressing you again - look for the NFB and follow it.
The CCS does not participate in the global NFB so there's no any reason to separate the CCS section and the voltage regulation one.
The NFB is in the voltage regulation part - just observe it thoroughly.

Salas 19th May 2018 10:55 PM

I see its at the same place as yours. The CCS and the CFP output section are on a same line and between that line and the Vref etc. there's a probe.

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