I node there was something wrong. More data,
please. Is this a physical SMPS, or a design, or a simulation? I
guess it might be physical, in which case SPICE simulation may
not be of much help. An SMPS produces a spectrum of all the
harmonics of the switching frequency, usually of fairly constant
amplitude up to a high harmonic (maybe the 51st; even harmonics
are usually weaker) and above that, the amplitudes roll off
quite steeply. So the next question is, what do? you count as
'noise'; harmonics above the 11th, say, or hash that is not
significantly harmonic related? The third one is, are you
measuring the noise at the mains input, as is suggested by your
mention of 'filter'? I'd better stop at three questions, lest
Father William kicks me downstairs.
This sounds like an EMC problem, rather than a
simulation problem, You could use LTspice to help with the
filter design, but it's usually more satisfactory to select a
commercially-available filter, since they use tricks that are
not in the public domain.
On 2025-02-21 19:55, Bell, Dave via
groups.io wrote:
Reposting with the right Subject spelling!
?
?
I just got tasked with trying to
characterize (and filter) a noisy switch-mode power supply,
?
There has been some chatter here about
noise generation over the years, but one simulation mode I
don’t recall seeing is use of the OTA Special Function with
its various noise specs.
Does anyone have suggestions on how to use
this Library device?
?
Thanks,
Dave
?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
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On Fri, Feb 21, 2025 at 02:54 PM, Bell, Dave wrote:
Does anyone have suggestions on how to use this Library device?
I recommend examining the subcircuit models for LTspice's built-in UniversalOpamps, found in UniversalOpamp.lib.? Pair that with the symbols for each UniversalOpamp to see the typical parameter values.
?
It might also help to check a few physical op-amps that use the OTA.? For example, look at the LT1001 or LT1028 models which can be found inside the file LTC.lib.
?
These library files are in your computer's LTspice library, in the folder ...\lib\sub\ .
?
Using it in a schematic is simpler because you don't need to deal with all those extra grounded nodes that add up to 8.? Just add the OTA or OTA2 symbol to your schematic.? Then right-click on the symbol and add whatever parameters you want it to have.? The Help page shows the default values for each parameter, when they are not specified.
?
Andy
?
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On Fri, Feb 21, 2025 at 02:54 PM, Bell, Dave wrote:
There has been some chatter here about noise generation over the years, but one simulation mode I don’t recall seeing is use of the OTA Special Function with its various noise specs.
The OTA is not a simulation mode.? It is a device.
?
Think op-amp, but with a current output instead of voltage.? That's an Operational Transconductance Amplifier.
?
It happens that many OTAs in real life are meant to be used open-loop instead of closed-loop, and many of those have the added feature of a variable transconductance gain, which makes them usable as a VCA (voltage controlled amplifier), or modulator or multiplier.
?
You have probably used LTspice's OTA and not realized it.? It is at the heart of many of LTspice's op-amp models, including its Universal op-amps, and some of the models of physical op-amps too.? Add a load at the output of an OTA, and now you have a traditional op-amp with a voltage output.? And it is more SPICE-friendly.? (SPICE is more happy with Norton sources than Thevenin sources.)
?
The OTA's noise parameters are well documented in LTspice's Help.? It is considered one of the A-devices (Special Functions).? The bottom half of the Help page about A. Special Functions lists the OTA's parameters.
?
I do not think the OTA has anything in common with noise from a SMPS.? SMPS "noise" is predictable noise from switching currents.? It is not random.? The noise of an op-amp (either normal or OTA) is a random noise.? In SPICE, they are as much different from one another as you can make them.
?
Andy
?
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Reposting with the right Subject spelling!
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]>
On Behalf Of Bell, Dave via groups.io
Sent: Friday, February 21, 2025 11:54 AM
To: [email protected]
Subject: EXTERNAL: [LTspice] Node modelling
?
I just got tasked with trying to characterize (and filter) a noisy switch-mode power supply,
?
There has been some chatter here about noise generation over the years, but one simulation mode I don’t recall seeing is use of the OTA Special Function with its various noise specs.
Does anyone have suggestions on how to use this Library device?
?
Thanks,
Dave
?
|
I just got tasked with trying to characterize (and filter) a noisy switch-mode power supply,
?
There has been some chatter here about noise generation over the years, but one simulation mode I don’t recall seeing is use of the OTA Special Function with its various noise specs.
Does anyone have suggestions on how to use this Library device?
?
Thanks,
Dave
?
|
Re: 12AU7 tube heater model
On Fri, Feb 21, 2025 at 11:56 AM, Carlo wrote:
Is that a sort of LTspice "internal" option not tracked as SPICE Netlist directive ?
Yes.
?
SPICE (and by extension LTspice) adds GMIN and others such as GSHUNT, GFARAD, and GFLOAT wherever they are needed, and that is done internally and they do not appear in the netlist.? That's just how it is done.? They are not explicit components.
?
Andy
?
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Re: using LTSPICE symbols for representation of spice netlist of OPAMP
On Fri, Feb 21, 2025 at 10:30 AM, john23 wrote:
How do I involve the opamp2 symbol into the symbol menu window shown below?
?
I'm sorry, but that question does not make sense.
?
The photo does not show a symbol menu.? It is a photo of your auto-generated symbol.? If you want to not use the auto-generated symbol, then do not add it to your schematic.? If it is on your schematic already, delete it from the schematic.
?
Add the opamp2 symbol to your schematic.? Edit the name next to it, from "opamp2", to the name you use for your "wrapper" subcircuit (the one that "wraps around" the actual AD797).? I used "MyAD797" in the example I showed previously.? Also get the netlist of that "wrapper" subcircuit into your simulation - either paste it directly onto the schematic (as a SPICE Directive), or include it as an .INCluded file.
?
Andy
?
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Re: 12AU7 tube heater model
BTW, I checked the "Add GMIN across current sources" checkbox in Control Panel. However I can't see anything added or changed in the netlist (SPICE Netlist).
?
Is that a sort of LTspice "internal" option not tracked as SPICE Netlist directive ?
?
?
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Re: 3 Phase Voltage Sense model
Andre,
?
Not driving any device, monitoring outputs to determine what the input voltage levels are.
?
Larry
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Re: 3 Phase Voltage Sense model
Andy, straightened out the pin order on the schematic symbol to match the .sub file, really thought I had it straight but they were off.? Guess that's what happens when you're doing several things at one time.? Circuit simulates properly now with the 3Phase_Voltage_Sense.asy symbol.
?
Want to thank everyone for their feedback.
?
Larry
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Re: using LTSPICE symbols for representation of spice netlist of OPAMP
Hello Andy , very intresting Idea .Indeed I will keep the decomp pin open.
I am used to start with the netlist and generating a symbol automatickly.
How do I involve the opamp2 symbol into the symbol menu window shown below?
?
/g/LTspice/photo/294510/3888971?p=Created%2C%2C%2C20%2C2%2C0%2C0
?
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Re: using LTSPICE symbols for representation of spice netlist of OPAMP
Also, there is this:
?
If you can draw a schematic, then you can draw a symbol.? Don't be afraid to make a brand new symbol.? Taking the "easy way out" by only auto-generating symbols, demonstrates laziness.? Don't be "that person" who is too lazy to try to do better.
?
Andy
?
?
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Re: 12AU7 tube heater model
Indeed, but I think it is a dangerous option,
to be used only with great care. Parallel V sources can create
infinite loop current, and non-physical transformers are not
easy to detect, which being liable to produce credible but wrong
results.
On 2025-02-21 14:44, Andy I via
groups.io wrote:
There is another option to disable the topology check that
caused this error.
.options topologycheck=0
The description is: "Set to zero to skip check for floating
nodes, loops of voltage sources, and non-physical
transformer winding topology".
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
Re: 3 Phase Voltage Sense model
Andy, your right thought I had those matching, will correct and give it a try.
?
Larry
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Re: 12AU7 tube heater model
vOn Fri, Feb 21, 2025 at 09:35 AM, Carlo wrote:
BTW, on LTspice Control Panel->Hacks! tab there is a checkbox named "Add GMIN across current sources". Is it supposed to "address" such a problem/error related to the current source's infinite impedance ?
I do not think it was designed for that purpose.
?
It does not eliminate the error message.? The error message comes about because of a topology check.? When LTspice is checking the topology, it likely does not include things such as GMIN as if they were separate elements.
?
There is another option to disable the topology check that caused this error.
.options topologycheck=0
The description is: "Set to zero to skip check for floating nodes, loops of voltage sources, and non-physical transformer winding topology".
?
Andy
?
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Re: PWM Timing Causing Shoot-thru
Ahhh thank you guys for explaining the distinction. It seems obvious now the difference between the .sub and the .asy.
?
I have re-uploaded my zip with the .asy.
?
?
Thanks!
-May
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Re: 12AU7 tube heater model
On Fri, Feb 21, 2025 at 06:01 AM, Andy I wrote:
The spike around 160 mA is the "singularity" I mentioned earlier.
?
This shows how the Duncan Amps heater model fails, when the heater's temperature becomes too great.? The resistance hits the singularity, then goes negative, causing the heater to generate energy instead of dissipating it.
Very good. By using Gmin stepping iteration, the spike is at 166 mA. Starting from 167 mA the heater resistance becomes negative and, as you highlighted, the Duncan Amps heater model begins to fail.
?
By the way, you can eliminate that error message, by adding a 1T resistor across the heater. ?That stops LTspice from thinking the nodes are floating.
?
BTW, on LTspice Control Panel->Hacks! tab there is a checkbox named "Add GMIN across current sources".?Is it supposed to "address" such a problem/error related to the current source's infinite impedance ?
?
?
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Re: PWM Timing Causing Shoot-thru
It's not the model that's missing, it the symbol: IR2110.asy.
--
Regards,
Tony
On 21/02/2025 15:18, May via groups.io
wrote:
toggle quoted message
Show quoted text
I am still checking this thread.
?
I did include IR2110.sub in the zip file. I
just downloaded my zip, extracted it to a folder and was able to
run the simulation without any issues.
?
You are most likely absolutely correct about the "C" signals;
I have not yet touched those. Was focused on "A" and "B".
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Re: PWM Timing Causing Shoot-thru
On Fri, Feb 21, 2025 at 09:18 AM, May wrote:
I did include IR2110.sub in the zip file. I just downloaded my zip, extracted it to a folder and was able to run the simulation without any issues.
Please read carefully.? You did not upload the SYMBOL file, which is IR2110.asy.? That file is missing from the .zip that you uploaded.? Having the model file does no good when the symbol file isn't there.
?
Of course it works fine on YOUR computer, because you have that symbol file already, somewhere in YOUR computer.? But we don't.? When I open your schematic, there is an error message, and there are "holes" on your schematic where the IR2110 symbol was supposed to be.? And I can't run the simulation without it and get meaningful results.
?
Andy
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Re: using LTSPICE symbols for representation of spice netlist of OPAMP
On Fri, Feb 21, 2025 at 09:03 AM, john23 wrote:
Is there a way to plug somehow the attached CIR file to standart LTSPICE symbol.
(in AD797 they also have extra decompensation pin)
What could be done ??
No you can't use the normal op-amp symbol directly, because of that extra pin.? The normal op-amp symbol is "opamp2", and it works for the majority of op-amps.? But not this one.
?
Here is something to consider doing.? Make a copy of the opamp2 symbol.? Then edit that symbol (in LTspice's symbol editor) to add the extra decompensation pin, and save the symbol with a new name, in your own symbol library.
?
Alternatively, start searching through the vast numbers of Analog Devices op-amps that come with LTspice, until you find another one that has an extra pin but still looks like an op-amp.? Make yourself a copy of that one.
?
If you know that you will never use the decompensation pin, there is another alternative:? Wrap a 5-pin subcircuit around the Analog Devices AD797 model, and don't bring that extra pin out to the outer subcircuit.? Now you have a 5-pin subcircuit, which CAN be used with the built-in "opamp2" symbol.
?
.SUBCKT MyAD797 In+ In- V+ V- Out
X? In+ In- V+ V- Out Decomp? AD797
.LIB AD797.cir
.ENDS MyAD797
?
Andy
?
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John Woodgate
Bell, Dave
Carlo
Tony Casey