The simplistic Salas low voltage shunt regulator - Page 56 - diyAudio
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Old 17th June 2009, 09:12 PM   #551
iko is offline iko  Canada
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V(Load1) no parasitics
V(load2) various parasitics setup

This
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produces this
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This
Click the image to open in full size.

produces this
Click the image to open in full size.



This
Click the image to open in full size.

produces this
Click the image to open in full size.
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Old 17th June 2009, 11:25 PM   #552
jeepee is offline jeepee  Netherlands
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Hi Ikoflexer,

I'm following this thread with interest. It's wonderful to see your relentless efforts unfold over the last weeks to create the ultimate regulator.

Regarding the remote sensing, I'm surprised by your implementation.
Basically this regulator is a constant current source from the raw supply to the load, with a shunt in parallel.
The high output impedance current source is converted into a low output impedance voltage source, by shunting the excess current with Q4.
To do so, Q4 is part of a feedback loop.
Zener ZT and Q3's Vbe form the sense part. Any excess voltage on the regulator output is converted (after ZT's levelshift) into a correction current by Q3.
This error current charges/discharges the gate of Q4, thus correcting towards the desired output voltage.
J3 is merely a bias current source.
So I would expect that you place ZT and Q3 as remote sensor close to the part in the load where you want to achieve constant voltage.
Then Q3's error current is passed back over to the shunt regulator, to the gate of Q4.
All components stay in the regulator, only ZT and Q3 move over to "the other side".

This arrangement should keep the load voltage constant.

Of course you need to watch for instability, particularly with the parasitic components as suggested by AndrewT.

Your quest for perfection is starting to conflict with the 'modular' approach.
This seems to be a fact of life ;-) Whenever something needs to be modular and/or universal, you need to compromise...

Ultimately every stage in Salas's RIAA amplifier should have its own, local regulator.
No remote sense, just local implementation, where a dedicated regulator keeps the voltage on the 1st amplifier stage constant and another dedicated regulator takes care of the 2nd amplifier stage.
I don't think you can do better than that, but it isn't modular and universal anymore, alas...

Keep up the good work and "never stop exploring".
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Old 17th June 2009, 11:25 PM   #553
jeepee is offline jeepee  Netherlands
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Hi Ikoflexer,

please be careful now with the voltages you measure. What's the reference now?
V(load1) and V(load2) are referring to which node in the schematic?
It would be better to probe V(load1)-V(load1_ground_reference), so a differential voltage.
same for V(load2)-V(load2_ground_reference).

Remember the purpose of the shunt regulator is to keep the voltage across the load constant!
We don't care about the 'system ground' node, just the local ground node of the 'circuit under test'.

Can you please indicate the important node pair in your schematic(s).

Further I think your initial parasitic inductances where more realistic. 1nH/mm as a rule of thumb for wire inductance defies the idea of 'remote sensing' ;-)
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Old 18th June 2009, 01:43 AM   #554
iko is offline iko  Canada
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jeepee, it's nice that you decided to join the discussion. You're right on many counts. Indeed, I'm struggling here for weeks to get an improvement, something that would take an engineer a few hours. But it's fun for me, nonetheless.

In my opinion, for light loads, there is hardly any point in doing something else other than what we call v1, basically salas' initial schematic shown above. What I'm after is heavier loads, where a lower output impedance would make a real difference, and also a wider bandwidth (while nice, this is not so important for me). Each solder point is a potential resistance, and each piece of wire is too, forming a series of voltage dividers; that got me thinking that we're regulating the voltage at a point other than exactly where the load needs its voltage regulated. Perhaps it's not important, but then again, it's fun to explore this. One thing led to another and I arrived at the idea of remote sensing.

Thank you for reminding me that what we need is to maintain a constant voltage drop across the load. True, the plots above showed the voltage drop between the top of the load and main ground, which is not the same thing. I lost track of this point in the fever of trying all these things. Well, and now theory and simulation do agree. All sensing is remote in this next circuit, and look what it does.

Click the image to open in full size.

Click the image to open in full size.

BTW, regarding your thought that each stage should have its own regulator, I agree. In fact I've seen one commercial amp in which each stage had its own regulator; it makes sense. For light loads one can probably get away with one CCS and multiple shunts connected to it, but since this is a low parts count circuit, why not build an entire thing.

I will try to set the parasitics to values as close as possible to reality and redo all this; now everyone probably has their own ideas to what those values are, so do suggest some if you can think of anything.

Finally, I always do test for stability, after any changes.
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Old 18th June 2009, 11:45 AM   #555
iko is offline iko  Canada
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salas, know any of these guys?

http://www.youtube.com/watch?v=xs1aU...eature=related
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Old 18th June 2009, 11:53 AM   #556
Salas is offline Salas  Greece
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No I do not. I know very few DIYers in person, and a couple of audiophiles with systems like those in the video.
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Old 18th June 2009, 12:07 PM   #557
iko is offline iko  Canada
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Well, I was just kidding, I realize Athens is huge.

But know it's clear, I need to build myself a pair of serious speakers.
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Old 18th June 2009, 12:11 PM   #558
Salas is offline Salas  Greece
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How many m2 you got?
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Old 18th June 2009, 12:13 PM   #559
iko is offline iko  Canada
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Sorry, what's m2?
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Old 18th June 2009, 12:14 PM   #560
Salas is offline Salas  Greece
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Square metres.
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