"Ground" is a term like "money", that we all think we understand but that doesn't really have an independent reality. It improves circuit performance to pretend we'd never heard the word and to go back to first principles - get the currents to and fro and try to keep them away from each other (mostly).
Series vs. shunt is something of a red herring in that all regulators have both elements. The real issue is current flows and common impedances.
Thanks,
Chris
Series vs. shunt is something of a red herring in that all regulators have both elements. The real issue is current flows and common impedances.
Thanks,
Chris
Hi,
Kirchhoff - Sum of all currents in a circuit must be zero.
Loop Area - the area of the current loop.
A little thought experiment.
Given is a circuit that will modulate the current it draws from the power supply.
A small local bypass cap is fitted to ensure stability.
Case A
The supply is a LM317 Adjustable regulator, remote from the circuit.
Case B
The LM317 is converted to a current source and a TL431 based shunt regulator is fitted adjacent to the circuit supplied with a minimal loop area.
Questions:
Where does signal modulated supply current flow?
Does ground impedance matter much in either case?
For extra credit, which arrangement has a better ripple rejection?
Ciao T
Kirchhoff - Sum of all currents in a circuit must be zero.
Loop Area - the area of the current loop.
A little thought experiment.
Given is a circuit that will modulate the current it draws from the power supply.
A small local bypass cap is fitted to ensure stability.
Case A
The supply is a LM317 Adjustable regulator, remote from the circuit.
Case B
The LM317 is converted to a current source and a TL431 based shunt regulator is fitted adjacent to the circuit supplied with a minimal loop area.
Questions:
Where does signal modulated supply current flow?
Does ground impedance matter much in either case?
For extra credit, which arrangement has a better ripple rejection?
Ciao T
You left out Case C- the LM317 fitted adjacent to the circuit supplied with a minimal loop area.
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Most will recognize the joke Jan but for others ...
To keep T from getting too boasty, he's been pushing that p.s. arrangement for ... well going on a decade. Starting way back at the ol' asylum!
Cheers,
Jeff
@PMA I like what this thread has become! It's like overhearing a bunch of experts at the pub after a long night of drinking ... ;-)
To keep T from getting too boasty, he's been pushing that p.s. arrangement for ... well going on a decade. Starting way back at the ol' asylum!
Cheers,
Jeff
@PMA I like what this thread has become! It's like overhearing a bunch of experts at the pub after a long night of drinking ... ;-)
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Do a quick calculation for scale. Assume that, as is normal practice, the source impedance of the raw supply is relatively low, and the feed and return lines are either coaxial, twisted, or side-by-side. The after part is exactly the same whether you use shunt or series.
Local series regulation fed by a constant-voltage source is used in nearly all high precision, low-noise equipment outside of high end audio. Perhaps there's a reason.
Sy,
I did not "leave it out". There is a reason I did not mention it, as the location of the series regulator close or far from the circuit does not change the routes of current flow and the production of error voltages across the non-zero ground impedances...
I would have that much was obvious (Kirchhoff after all) but alas, some people are always out to prove me wrong...
Ciao T
I did not "leave it out". There is a reason I did not mention it, as the location of the series regulator close or far from the circuit does not change the routes of current flow and the production of error voltages across the non-zero ground impedances...
I would have that much was obvious (Kirchhoff after all) but alas, some people are always out to prove me wrong...
Ciao T
Hi,
I didn't. Didn't have to.
I have been using shunt regulators since the last millenium for precisely these reasons...
But it seems some others would be well advised to familiarise themselves with the content of said column...
Ciao T
I didn't. Didn't have to.
I have been using shunt regulators since the last millenium for precisely these reasons...
But it seems some others would be well advised to familiarise themselves with the content of said column...
Ciao T
However, it greatly changes the voltages presented at the circuit and the return reference. So perhaps you might wish to include this as a possibility.
Sy,
Well, you may AssUMe as you wish, however to simply assume the PSU as "low" (I like the precision of this specification) will not do, unless you have pre-regulated it.
If it is not pre-regulated, what will the impedance be?
Moreover, in one line we have the regulator which has a very high look-back impedance. Things are not easy as you pretend.
And the key is, with a shunt regulator there will be essentially no signal related supply current (or rather, the magnitude will drastically lowered compared to the actual supply current modulation at the entrance to the supplied circuit) that flows in the ground, with a series regulator the full magnitude of the signal related supply current is impressed.
Kirchoff, remember? And Ohm. Elementary, really.
Perhaps there is a reason. Perhaps there is not. Your point is?
Incidentally, shunt regulated power supplies are neither confined to nor a specific feature or invention of High End Audio, except in the minds of those who see dangerous con-artists everywhere that will rip off all these poor idiot peepull who know no better if given the least chance.
Ciao T
Well, you may AssUMe as you wish, however to simply assume the PSU as "low" (I like the precision of this specification) will not do, unless you have pre-regulated it.
If it is not pre-regulated, what will the impedance be?
Moreover, in one line we have the regulator which has a very high look-back impedance. Things are not easy as you pretend.
And the key is, with a shunt regulator there will be essentially no signal related supply current (or rather, the magnitude will drastically lowered compared to the actual supply current modulation at the entrance to the supplied circuit) that flows in the ground, with a series regulator the full magnitude of the signal related supply current is impressed.
Kirchoff, remember? And Ohm. Elementary, really.
Perhaps there is a reason. Perhaps there is not. Your point is?
Incidentally, shunt regulated power supplies are neither confined to nor a specific feature or invention of High End Audio, except in the minds of those who see dangerous con-artists everywhere that will rip off all these poor idiot peepull who know no better if given the least chance.
Ciao T
Hi,
What it does not change is the current and the real "ground"...
It matters not where your series regulator is, the current loop does not stop at the regulator. Having a series regulator close to the supplied circuit helps zip to keep signal modulated PSU currents out of the "ground".
Ciao T
What it does not change is the current and the real "ground"...
It matters not where your series regulator is, the current loop does not stop at the regulator. Having a series regulator close to the supplied circuit helps zip to keep signal modulated PSU currents out of the "ground".
Ciao T
My point is that your analysis is not incorrect, it's just incomplete.
No, and that's not what I said anyway. What I did say was they are rare elsewhere and almost nonexistent in critical applications. My first exposure was from Gottlieb's power supply book.
Considerably lower than a CCS source.
Hi,
My point was that I did not present any analysis, but I posited two extreme but eminently practical cases (and at least one of them is extremely common) and asked the reader to consider them and think it through and (if they cared) to answer the questions.
If this had been an exam question you would have scored zero points.
And that is supposed to make what point exactly?
Ciao T
My point was that I did not present any analysis, but I posited two extreme but eminently practical cases (and at least one of them is extremely common) and asked the reader to consider them and think it through and (if they cared) to answer the questions.
If this had been an exam question you would have scored zero points.
And that is supposed to make what point exactly?
Ciao T
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