Re: Looking for ideal fully differential amplifier spice model
On Thu, Dec 26, 2024 at 08:06 AM, Andy I wrote:
I would think that a non-Op-Amp would be needed in that case, perhaps a diff amp with a preset gain of 1 or 2.
The term "OpAmp" is misused by me. TI and AD use Amplifier. They make multiple types designed to feed differential ADCs and almost all rely on external resistors to sett gain. Gain is dependent on usage and ADC chosen.
What is meant by the word "true" in "'true' Fully-Differential OpAmp"? Is there another kind that is not "true"?
Another term misused by me but it's to point out the requirements a simple E/G sourced amp may not have compared to a "real life" one.
"Perhaps it is teetering on the brink of instability, and it only remains stable when the resistors are exactly matched?"
Could be. Analysis of multiple manufacturer's spice models result in the outputs stuck to the rails or analysis fails.
|
Re: Autotransformer deep questions!
On 26/12/2024 21:40, Bell, Dave via
groups.io wrote:
Please see my recent upload,
Autotransformer.zip
I need some tutorials regarding
autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and
tried to model TR1
The model differed from my expectations in
several ways.
1: Why do the
tap-to-tap voltages differ, with equal inductances?
2: Why is the
separate 18V winding so different?
2a: Why is it more
different when I separate the Kxxx directives?
3: Why do the
outputs throw infinities with small or megohm loads, but not
when 1G or open??
It's not quite the same as your schematic, but I uploaded an autotransformer
model earlier this year. If you searched the Files section for
examples of "Autotransformer" you wouldn't have found it, because I
called it a "Variac", which was actually an old trademarked name,
but I guess it stuck.
Briefly, I investigated Helmut Sennewald's previous model and found
where that was going wrong, and fixed it. (I continue to be amazed
how much work Helmut put into this group.)
You might find the workings of the model useful in modelling
autotranformers with more taps, or just in general. It was
deceptively difficult to accurately model a variac properly, which
is presumably why I didn't find any other working models out there.
--
Regards,
Tony
|
Re: Autotransformer deep questions!
I’ll update it tomorrow; getting late here.
I got answers to most of my issues, so it may be a useful stating point.
Dave
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io> On Behalf Of
MD MUBDIUL HASAN via groups.io
Sent: Friday, December 27, 2024 8:01 PM
To: ltspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
On Thursday, December 26, 2024 at 09:41:03 PM GMT+1, Bell, Dave via groups.io <dave.bell@...>
wrote:
Please see my recent upload, Autotransformer.zip
I need some tutorials regarding autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and tried to model TR1
The model differed from my expectations in several ways.
1: Why do the tap-to-tap voltages differ, with equal inductances?
2: Why is the separate 18V winding so different?
2a: Why is it more different when I separate the Kxxx directives?
3: Why do the outputs throw infinities with small or megohm loads, but not when 1G or open??
Dave
|
Re: Autotransformer deep questions!
Dave Great job 👏 I will look at it.
On Thursday, December 26, 2024 at 09:41:03 PM GMT+1, Bell, Dave via groups.io <dave.bell@...> wrote:
Please see my recent upload, Autotransformer.zip
I need some tutorials regarding autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and tried to model TR1
The model differed from my expectations in several ways.
1: Why do the tap-to-tap voltages differ, with equal inductances?
2: Why is the separate 18V winding so different?
2a: Why is it more different when I separate the Kxxx directives?
3: Why do the outputs throw infinities with small or megohm loads, but not when 1G or open??
Dave
|
Re: Looking for ideal fully differential amplifier spice model
Andy, I’m away from my library now so I can’t consult dusty sources, but the idea of polarity indifference for infinite gain amplifiers is illustrated in the technique using “stamps” or templates to build or modify admittance matrices for circuit elements. The simplest case adds a passive one port—typical r,L,and c elements by constructing a stamp of four entries in a square array to add to the existing matrix. The stamp overlays the matrix to add the two positive diagonal terms and the two off diagonal negative terms at the appropriate locations corresponding to the element nodes. For active two port devices, the stamp values are no longer symmetric and the four matrix locations correspond to the two controlling nodes and the two controlled or output nodes. In the case of infinite gain, the stamp doesn’t add infinite entries but rather prompts the combining or deleting of appropriate rows and/or columns. This is where the polarity indifference shows up. Notice this is just a mechanical mnemonic device, the actual theoretical circuit analysis is the actual basis.
As an aside, I wrote a C program that analyzes linear networks symbolically. It accepts r,L,c,g,m,ideal opamps, and controlled sources to produce two port parameters— z,y,h,g,t,and s symbolically.
As an example the ideal opamp(the nullor model) still drives the summing junction to virtual ground regardless of the polarity of its inputs. Using a controlled source in place of the nullor produces the expected sign changes in the results as a function of the input polarity.
Again, this is still empirical rather than rigorous.
Jeff
|
Re: Looking for ideal fully differential amplifier spice model
It would make an ideal "Ideal Rectifier" ...
Jeff, that is an interesting description and is new to me. But the part that most puzzles me is this one:
The interesting property of an ideal opamp with infinite gain is the polarity of the input doesn’t change the circuit function.
It seems that the polarity should matter. I get it that the differential input voltage tends towards zero, to the degree that the voltage gain from input to output approaches infinite. But the polarity of an incremental input voltage (call it dv), should determine the polarity of the differential output voltage, shouldn't it? Surely it can't really be arbitrary, can it? Maybe I'm not understanding what you're saying.
Andy
|
Re: Autotransformer deep questions!
Le 27/12/2024 à 00:34, Bell, Dave via
groups.io a écrit :
Ahh,
unloaded, so (little to) no reflected impedance!
In this
simplified circuit, L2 is on top of L1, and is the 220V
input, so the same current flows in L1.
This is not true. In the bottom inductor you have all the
magnetizing current (about 7A), but in the top inductors there is
almost no current, because there is a negligible load.
In a typical autoformer, as someone mentioned earlier, output
current circulates in reverse in the primary, for a smaller
resulting current.
Use Kirchoff at the junction of L1 and L2.
|
Re: Looking for ideal fully differential amplifier spice model
Jeff, that is an interesting description and is new to me. But the part that most puzzles me is this one:
The interesting property of an ideal opamp with infinite gain is the polarity of the input doesn’t change the circuit function.
It seems that the polarity should matter. I get it that the differential input voltage tends towards zero, to the degree that the voltage gain from input to output approaches infinite. But the polarity of an incremental input voltage (call it dv), should determine the polarity of the differential output voltage, shouldn't it? Surely it can't really be arbitrary, can it? Maybe I'm not understanding what you're saying.
Andy
|
Re: Autotransformer deep questions!
Loads were resistive, from the taps points to return.
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io> On Behalf Of
Andy I via groups.io
Sent: Thursday, December 26, 2024 4:14 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
On Thu, Dec 26, 2024 at 07:10 PM, Bell, Dave wrote:
I tried both K directives, one separate for just L1 & L6, and all (L1..4 & L6) in one line.
Don't even bother with the one that is physically impossible. It doesn't matter if it simulates - it is wrong!
There was a small difference in L6 voltage, but similar issues with infinities with small loads.
Where are the loads connected?
|
Re: Autotransformer deep questions!
You are still struggling with a complicated
transformer. Start with a simple winding with just one tap, with
the mains supply across the whole winding, and no separate
'secondary' winding. When you get that simple version to work,
then expand. Nothing should ever 'blow up' in such circuits.
On 2024-12-27 00:10, Bell, Dave via
groups.io wrote:
I later extended the TRAN to over 1 second,
then starting data at 1s.
The currents definitely took 6-8 cycles to
settle down, but voltages were essentially the same.
“But there is zero
coupling between L6 and any of L2, L3, and L4. That is not
physically possible! This might be why it "blows up".”
I tried both K directives, one separate for
just L1 & L6, and all (L1..4 & L6) in one line.
There was a small difference in L6 voltage,
but similar issues with infinities with small loads.
Dave
Several more things to note:
It is never a good idea to simulate for
only 1/2 of a cycle, or even 1 cycle -
especially
when inductors are involved! A far better thing to do is to
simulate for 10s to 1000s of cycles (or more), and then
apply your .MEAS commands to only the last cycle. e.g., you
might use ".tran 0 10 9.98" or similar.
Because you extracted their amplitudes at
only one specific point in time, I strongly recommend
disabling waveform compression. With waveform compression
enabled, the saved points miss the peaks entirely, and now
your measurements depend on interpolation. It's far better
to use ".MEAS ... RMS" over a full cycle, instead of ".MEAS
... AT".
By using "AT", you also introduced errors
due to phase shift. With both resistances and inductances,
there is phase shift.
You constructed a physically impossible
magnetic circuit. You have L1 and L6 tightly coupled, and
L1 is tightly coupled to each of L2, L3, and L4. But there
is
zero
coupling between L6 and any of L2, L3, and L4. That is not
physically possible! This might be why it "blows up".
--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying
|
Re: Autotransformer deep questions!
On Thu, Dec 26, 2024 at 07:10 PM, Bell, Dave wrote:
I tried both K directives, one separate for just L1 & L6, and all (L1..4 & L6) in one line.
Don't even bother with the one that is physically impossible. It doesn't matter if it simulates - it is wrong!
There was a small difference in L6 voltage, but similar issues with infinities with small loads.
Where are the loads connected?
Andy
|
Re: Autotransformer deep questions!
I later extended the TRAN to over 1 second, then starting data at 1s.
The currents definitely took 6-8 cycles to settle down, but voltages were essentially the same.
“But there is zero coupling between L6 and any of L2, L3, and L4. That is not physically possible! This might be why it "blows up".”
I tried both K directives, one separate for just L1 & L6, and all (L1..4 & L6) in one line.
There was a small difference in L6 voltage, but similar issues with infinities with small loads.
Dave
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io> On Behalf Of
Andy I via groups.io
Sent: Thursday, December 26, 2024 4:00 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
Several more things to note:
It is never a good idea to simulate for only 1/2 of a cycle, or even 1 cycle -
especially when inductors are involved! A far better thing to do is to simulate for 10s to 1000s of cycles (or more), and then apply your .MEAS commands to only the last cycle. e.g., you
might use ".tran 0 10 9.98" or similar.
Because you extracted their amplitudes at only one specific point in time, I strongly recommend disabling waveform compression. With waveform compression enabled, the saved points miss the peaks entirely, and now your measurements depend
on interpolation. It's far better to use ".MEAS ... RMS" over a full cycle, instead of ".MEAS ... AT".
By using "AT", you also introduced errors due to phase shift. With both resistances and inductances, there is phase shift.
You constructed a physically impossible magnetic circuit. You have L1 and L6 tightly coupled, and L1 is tightly coupled to each of L2, L3, and L4. But there is
zero coupling between L6 and any of L2, L3, and L4. That is not physically possible! This might be why it "blows up".
|
Re: Autotransformer deep questions!
Several more things to note:
It is never a good idea to simulate for only 1/2 of a cycle, or even 1 cycle - especially when inductors are involved! A far better thing to do is to simulate for 10s to 1000s of cycles (or more), and then apply your .MEAS commands to only the last cycle. e.g., you might use ".tran 0 10 9.98" or similar.
Because you extracted their amplitudes at only one specific point in time, I strongly recommend disabling waveform compression. With waveform compression enabled, the saved points miss the peaks entirely, and now your measurements depend on interpolation. It's far better to use ".MEAS ... RMS" over a full cycle, instead of ".MEAS ... AT".
By using "AT", you also introduced errors due to phase shift. With both resistances and inductances, there is phase shift.
You constructed a physically impossible magnetic circuit. You have L1 and L6 tightly coupled, and L1 is tightly coupled to each of L2, L3, and L4. But there is zero coupling between L6 and any of L2, L3, and L4. That is not physically possible! This might be why it "blows up".
Andy
|
Re: Autotransformer deep questions!
Dave,
Start your sinewave source ( V1 ) at some phase angle.
10, 20 ... 90 degree should resolve the loading issue.
With 10 degrees, I have a 10 ohm load at node F and a clear sinewave.
Mike
|
Re: Looking for ideal fully differential amplifier spice model
The ideal fully differential amplifier is another description of a theoretical device called the nullor. A nullor has two ports: one port, has zero conductance, zero voltage across its terminals, and zero current into its terminals, named a nullator; the second port, has zero impedance into its terminals, and arbitrary voltage and current at its terminals, called a norator. The nullator and the norator must exist in pairs which are called nullors. A nullor is an ideal opamp which has floating differential output instead of single ended.
The interesting property of an ideal opamp with infinite gain is the polarity of the input doesn’t change the circuit function. This is an operational rather than a numerical property which isn’t shown in ordinary numerical simulation. This property is shared with nullors which have no port polarity preference.
The nullator-norator pair were named in a 1964 paper by Carlin on singular network elements as part of unofficial competition among circuit theorists to find the most fundamental network elements. A european theorist Tellegen, had a fit and criticized carlin’s paper.
Textbook examples: Bruton, rc active circuits; mitra, analysis and synthesis of linear active circuits
|
Re: Autotransformer deep questions!
Ahh, unloaded, so (little to) no reflected impedance!
In this simplified circuit, L2 is on top of L1, and is the 220V input, so the same current flows in L1.
I tried loading the (buck, 210V) tap between L2 and L1.
With any load <6 Meg, it blows up into infinities again, or in some config, threw a singular matrix error.
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io>
On Behalf Of Jerry Lee Marcel via groups.io
Sent: Thursday, December 26, 2024 3:00 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
Le 26/12/2024 à 23:49, Bell, Dave via groups.io a écrit :
I plotted the currents in L1 and L2: Essentially identical , but + and – 6+amps?!?
Impedance of a 100mH inductor at 50Hz=31 ohms
220V into 31 ohms= about 7 amps
Is that some kind of circulating current in coupled inductors?
Only mA in L6, the separate 18V winding
Use the cursor instead of MEAS statements, which are so easily wrongly-written.
On 2024-12-26 22:32, Bell, Dave via groups.io wrote:
.TRAN for 1010ms made no difference; same measurements at 1005m as at 5m
Two things I notice instantly:
Primary voltage should be 311V. Voltages in SPICE are peak.
You don't run a 50Hz transient for only 10ms.
Le 26/12/2024 à 21:40, Bell, Dave via groups.io a écrit :
Please see my recent upload, Autotransformer.zip
I need some tutorials regarding autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and tried to model TR1
The model differed from my expectations in several ways.
1: Why do the tap-to-tap voltages differ, with equal inductances?
2: Why is the separate 18V winding so different?
2a: Why is it more different when I separate the Kxxx directives?
3: Why do the outputs throw infinities with small or megohm loads, but not when 1G or open??
Dave
--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying
|
Re: Autotransformer deep questions!
Le 26/12/2024 à 23:49, Bell, Dave via
groups.io a écrit :
I plotted
the currents in L1 and L2: Essentially identical , but + and
– 6+amps?!?
Impedance of a 100mH inductor at 50Hz=31 ohms
220V into 31 ohms= about 7 amps
Is that some
kind of circulating current in coupled inductors?
Only mA in
L6, the separate 18V winding
Use
the cursor instead of MEAS statements, which are so easily
wrongly-written.
On 2024-12-26 22:32, Bell, Dave via
groups.io wrote:
.TRAN for 1010ms made no difference; same
measurements at 1005m as at 5m
Two things I notice instantly:
Primary voltage should be 311V. Voltages in SPICE are peak.
You don't run a 50Hz transient for only 10ms.
Le 26/12/2024 à 21:40, Bell, Dave via
groups.io a écrit :
Please see my recent upload,
Autotransformer.zip
I need some tutorials regarding
autotransformer modelling!
I was intrigued by Hassan's AC
Stabilizer and tried to model TR1
The model differed from my expectations
in several ways.
1: Why do the
tap-to-tap voltages differ, with equal inductances?
2: Why is the
separate 18V winding so different?
2a: Why is it
more different when I separate the Kxxx directives?
3: Why do the
outputs throw infinities with small or megohm loads, but
not when 1G or open??
Dave
--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying
|
Re: Autotransformer deep questions!
Same readings, within cursor positioning tolerance…
Also extended the .tran until current transient decayed, around 60+ms.
I plotted the currents in L1 and L2: Essentially identical , but + and – 6+amps?!?
Is that some kind of circulating current in coupled inductors?
Only mA in L6, the separate 18V winding
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io>
On Behalf Of John Woodgate
Sent: Thursday, December 26, 2024 2:41 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
Use the cursor instead of MEAS statements, which are so easily wrongly-written.
On 2024-12-26 22:32, Bell, Dave via groups.io wrote:
.TRAN for 1010ms made no difference; same measurements at 1005m as at 5m
Two things I notice instantly:
Primary voltage should be 311V. Voltages in SPICE are peak.
You don't run a 50Hz transient for only 10ms.
Le 26/12/2024 à 21:40, Bell, Dave via groups.io a écrit :
Please see my recent upload, Autotransformer.zip
I need some tutorials regarding autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and tried to model TR1
The model differed from my expectations in several ways.
1: Why do the tap-to-tap voltages differ, with equal inductances?
2: Why is the separate 18V winding so different?
2a: Why is it more different when I separate the Kxxx directives?
3: Why do the outputs throw infinities with small or megohm loads, but not when 1G or open??
Dave
--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying
|
Re: Autotransformer deep questions!
Use the cursor instead of MEAS statements,
which are so easily wrongly-written.
On 2024-12-26 22:32, Bell, Dave via
groups.io wrote:
.TRAN for 1010ms made no difference; same
measurements at 1005m as at 5m
Two things I notice instantly:
Primary voltage should be 311V. Voltages in SPICE are peak.
You don't run a 50Hz transient for only 10ms.
Le 26/12/2024 à 21:40, Bell, Dave via
groups.io a écrit :
Please see my recent upload,
Autotransformer.zip
I need some tutorials regarding
autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer
and tried to model TR1
The model differed from my expectations
in several ways.
1: Why do the
tap-to-tap voltages differ, with equal inductances?
2: Why is the
separate 18V winding so different?
2a: Why is it
more different when I separate the Kxxx directives?
3: Why do the
outputs throw infinities with small or megohm loads, but not
when 1G or open??
Dave
--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying
|
Re: Autotransformer deep questions!
.TRAN for 1010ms made no difference; same measurements at 1005m as at 5m
переключити цитоване повідомлення
Показати цитований текст
From: LTspice@groups.io <LTspice@groups.io>
On Behalf Of Jerry Lee Marcel via groups.io
Sent: Thursday, December 26, 2024 2:04 PM
To: LTspice@groups.io
Subject: EXTERNAL: Re: [LTspice] Autotransformer deep questions!
Two things I notice instantly:
Primary voltage should be 311V. Voltages in SPICE are peak.
You don't run a 50Hz transient for only 10ms.
Le 26/12/2024 à 21:40, Bell, Dave via groups.io a écrit :
Please see my recent upload, Autotransformer.zip
I need some tutorials regarding autotransformer modelling!
I was intrigued by Hassan's AC Stabilizer and tried to model TR1
The model differed from my expectations in several ways.
1: Why do the tap-to-tap voltages differ, with equal inductances?
2: Why is the separate 18V winding so different?
2a: Why is it more different when I separate the Kxxx directives?
3: Why do the outputs throw infinities with small or megohm loads, but not when 1G or open??
Dave
|
Tony Casey
Bell, Dave
John Woodgate
