Re: Regarding basic simulation of ACST
Hello Andy,
I will take care of no uploading RAW or LOG or . NET files. Also I am aware of fixing time step too small errors, thanks for providing the document again. However, my basic idea here was to get rid of the curly braces error.
jagdish
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Re: Square wave into a bridge rectifier (by member "FlightRisk")
Fred,
By moving the ground connection from below C1 to below V1, you also need to change your .IC statement, so that the initial voltage is applied across the capacitor:
? ??.ic V(C1node,N002)=0
You don't want to start the simulation with V(C1node)=0 when the other end of C1 is not grounded.? The results are rather bad if left that way.? That's why you got the unexpected results.
Two other suggestions:
It's a Really Good Idea to name the net connected to the bottom of C1, after moving the ground from there to below V1.? By leaving the net unnamed, it inherits the temporary nodename N002, which can change on you if you make other changes to the schematic.
The other thing I recommend is not using the default diode "D".? D is an idealized diode model with zero resistance and capacitance, which are known to sometimes cause simulation problems.? Sometimes it's OK, sometimes not.? Any of the diodes from the "Pick New Diode" menu have realistic values.? The D diode model is the standard one from SPICE, 50 years ago.? As it happens, with the right .IC statement, any diode is good enough; but with the wrong .IC statement AND the "D" diode model, LTspice struggles.
Andy
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Re: Square wave into a bridge rectifier (by member "FlightRisk")
Hmmm. Like I said, I have a lot to learn about the software. I uploaded capacitor_charging.asc to the files section. What I have in that schematic works. I can create a current probe in the resistor and just put one voltage probe at the top of the capacitor. If I move the ground to the left side where I left a wire stub under the voltage source and use a differential probe from the top to the bottom of the capacitor, I get the unexpected results.
Fred
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Re: Square wave into a bridge rectifier (by member "FlightRisk")
Fred wrote, "I figured you could only have one ground, but put it on the input side based on examples from the web"
Yes, if you have more than one ground, just be aware that they get connected together, which might or might not be what you want.
It is pretty much arbitrary what point you choose to be your "ground", as long as you remember that any voltage you probe should be a voltage BETWEEN two points.
? ? "If anyone else sees tutorial like I saw with the ground before the bridge and using the differential probe by holding down the left mouse button for the red probe, then moving the resulting black probe to the output ground, it doesn't work, at least not with a signal over a few hundred Herz."
I can tell you that what you described definitely DOES work.? It's what we frequently remind people to do.? If it didn't work, then I guess something went wrong when you tried it.? There is no reason why it would not work or that it would be bandwidth limited.? It's not.
Some SPICE models can have hidden connections to global ground.? Then, changing the point that gets connected to ground would make a difference when they are part of the simulation.
Andy
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Re: Square wave into a bridge rectifier (by member "FlightRisk")
Thank you for correcting my mistake in posting. I was coming back to say I found the issue and have a tad more to learn about LTSpice. I figured you could only have one ground, but put it on the input side based on examples from the web (Aren't all youtube videos vetted? ;) ). When I moved the ground to the output side, I got what I expected. If anyone else sees tutorial like I saw with the ground before the bridge and using the differential probe by holding down the left mouse button for the red probe, then moving the resulting black probe to the output ground, it doesn't work, at least not with a signal over a few hundred Herz.
Fred
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Square wave into a bridge rectifier (by member "FlightRisk")
Someone named "FlightRisk" attempted to send a message to the [LTspice] group an hour ago, wondering why there are "wild voltages and currents" with her/his rectifier circuit.? But they probably did not read the group's main webpage, and ignored the advice to NEVER USE ATTACHMENTS in messages.? So their message was rejected. FlightRisk, if you have a schematic to show us, please upload it to the " Temp" folder in the group's? Files section.? Then tell us that you did it.? If you have pictures, we are not interested, so please don't upload them.? All we need is your schematic.? It's a *.ASC file.? By running the simulation, we can see the same thing you saw, making pictures unnecessary.? But if you absolutely need to show pictures, they should be uploaded to the group's Photos section.? However, the schematic (ASC file) is worth 1000 pictures. I'm guessing here, but there is a fair chance that you did not pay attention to your grounds.? The bridge rectifier should not be grounded on both sides of the rectifier, so you need to pay attention when plotting those voltages.? Plotting ground-referenced voltages on the side that doesn't have a ground, just messes up the plots.? If you did ground both sides of the rectifier, the short circuit you added probably messes it up.? Alternatively, if your source includes a transformer, the transformer's SPICE model might be ringing in response to the square waves.? Also transformers can be tricky to simulate because the source "turns on" instead of running continuously.? Best to see your schematic (*.asc file). We might not hear back from FlightRisk for a while, not because of their name but because they set their email delivery to the daily summary. Andy
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Re: Difference between finding DC point before AC, and pure DC simulation
Over the years I've noticed all versions of SPICE appear to use different algorithms to solve the DC bias point for .dc, .ac, and .tran analyses.
The use of the .savebias and .loadbias commands can be useful, especially for circuits that take a long time to converge to a DC solution. Often times the .tran command finds the DC solution faster than the .DC - in this case the .savebias time=xyz is useful. I seem to recall needing to make sure the options in the simulator are set to save all node voltages and currents if using subcircuits.
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Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
I would separate this in two answers:
1) if you are getting from a manufacturer a standard transformer- ask your manufacturer for supporting you with measured data about the specifications given.And the simulation model parameter.
Additional also on getting the coupling capacitance primary to secondary. As this is your pain point later on in EMI....
If they can?t support you- then you have to measure it on your own. How to do? Please see book "Trilogy of Inductors", 5th edition, section I.4.3 Transformer Parasitic parameter and equivalent circuit, pg. 121ff.
2) for a customized transformer ? Well, with same target specifcations, you will find different solutions by winding arrangement, insulation layer, core material, bobbin, etc etc.
This all has an impact on the final specfcations. And so also on the parasitics incorporated in the individual design. The best way then is to measure the sample as described above. Everything else, is guessing...
?
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Re: Difference between finding DC point before AC, and pure DC simulation
This is something that has puzzled me too, for years, but I did not figure out how.? Also there are cases where the initial operating point solution needed for .TRAN differs.??I think the algorithms are essentially the same, but with subtle difference in some settings.? (Maybe some of the .options, ITLn for example.)? Also, a .DC sweep likely starts from a different initial DC value, and then sweeps through the point that you're using for the .AC simulation, which gives .DC an advantage.? If your circuit has trouble converging on the operating point, it matters where it is coming from, and what were the initial guesses.
When SPICE finds the operating point, whether it's for .OP or .DC or .AC or .TRAN or .NOISE, I believe all the capacitors are removed and all inductors replaced by shorts (but accounting for their parasitics).? It's the "finds DC solution" step that you need to worry about.
Andy
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Re: Ohms/volt? (was: Spark gap physics.)
Ohms per volt is a figure of merit for moving coil voltmeters. The number is dominated by the resistance of the moving coil; that is the input resistance on the most sensitive scale divided by the full scale voltage. Resistive dividers are then used for less sensitive scales, and the ohms per volt value is retained for higher voltage scales so long as the scaling is done with a simple series resistance.?
When basic electronic analog volt meters came along, the input resistance tended to be the same on all voltage scales and that figure of merit was no longer significant. That is also true of modern DVMs.
Jim Wagner
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Difference between finding DC point before AC, and pure DC simulation
Hello!
Question is simple, I have a circuit (I can't upload it here due to company restrictions unfortunately), and it perfectly converges in DC analysis,
even if I start it not from the zero voltages point, but AC analysis with .step command to get capacitance curve failed at DC solution.
Transient analysis also works perfectly, so the point is - what is the difference between DC analysis and DC solution before AC analysis?
As I understand, to simulate AC, program exclude capacitances and inductances, finds DC solution, and the does phasor analysis with C and L included, so I don't see any difference between conventional DC analysis and this step before AC.
Thank you in advance.
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Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
Jerry,
?
Thanks for your comment, I didn't know that the inductance decreases at higher frequencies.
The modification of the model to correctly reflect the decreases at higher frequencies is beyond my expertise. I leave that to someone else.
But I think my model is already a big step forward compared to using a bunch of coupled coils with odd values on the schematics.?
?
Ite
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Re: Ohms/volt? (was: Spark gap physics.)
Ohms being Volts per Ampere, Ohms per Volts would resolve as
1/Ampere.
As you say, I don't know that a unit has been deemed useful for
Ampere power minus one
Le 20/07/2023 à 09:29, John Woodgate a
écrit?:
toggle quoted message
Show quoted text
Equal to x peramps?? While
resistance, capacitance, reactance and impedance have
inverse units (conductance, elastance, susceptance and
admittance), I don't know of any for inductance, voltage or
current.
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
Rayleigh, Essex UK
I hear, and I forget. I see, and I remember. I do, and I
understand. Xunzi (340 - 245 BC)
On 2023-07-20 05:15, Richard Andrews
via groups.io wrote:
Is there such a thing as x ohms/volt?
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Re: Ohms/volt? (was: Spark gap physics.)
Equal to x peramps?? While
resistance, capacitance, reactance and impedance have inverse
units (conductance, elastance, susceptance and admittance), I
don't know of any for inductance, voltage or current.
======================================================================================
Best wishes
John Woodgate OOO-Own Opinions Only
Rayleigh, Essex UK
I hear, and I forget.
I see, and I remember.
I do, and I understand.
Xunzi (340 - 245 BC)
On 2023-07-20 05:15, Richard Andrews
via groups.io wrote:
toggle quoted message
Show quoted text
Is there such a thing as x ohms/volt?
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Re: Ohms/volt? (was: Spark gap physics.)
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Re: Ohms/volt? (was: Spark gap physics.)
Well, it’s the reciprocal of current, which is a rather obscure unit.
It used to be common as a figure of merit for (analog, moving coil!) milli- or micro-ammeters.
The higher the number, the greater the sensitivity of the movement, and the lower the load a voltmeter using that microammeter places on a measurement. A decent analog multimeter like a Fluke would be rated 20,000 Ohms per Volt.
?
toggle quoted message
Show quoted text
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Ohms/volt? (was: Spark gap physics.)
Is there such a thing as x ohms/volt?
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Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
To be clear, I am not talking
about the sort of 'design' posted by ik.weide. I mean choosing
the core size and material, and the number of turns of the
gauge of wire that will fit on the bobbin.
======================================================================================
Best wishes
John Woodgate OOO-Own Opinions Only
Rayleigh, Essex UK
I hear, and I forget.
I see, and I remember.
I do, and I understand.
Xunzi (340 - 245 BC)
On 2023-07-18 15:06, John Woodgate
wrote:
toggle quoted message
Show quoted text
This is a suspended thread,
but I am now able to look at the proposed tutorial The first
question is, what sort(s) of transformer? While the basic
theory is the same for all, the practical design methods
vary considerably. There is no point in writing a tutorial
that no-one is interested in.
I see the occasional query
about a power supply having a mains transformer with
inductances in the mH or less range, so there may be some
interest in mains transformers.? I also see the occasional
query about audio output transformers for tubes/valves.? I
don't think anyone would try to wind their own toroidal, so
we are talking 'E's and I's', maybe with the occasional 'T's
and U's.
I'm not going to deal with
transformers for SMPS, because they need a totally different
approach, as do RF transformers with ferrite cores or no
core.
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
Rayleigh, Essex UK
I hear, and I forget. I see, and I remember. I do, and I
understand. Xunzi (340 - 245 BC)
On 2023-04-29 19:50, Jim Wagner
wrote:
BUT, what are those “easily measured or calculated parameters”?
I am a circuit designer and have no idea what they are (or how
to do the measurements)!. I strongly suspect that I am not
alone. How about a tutorial for the wiki?
Jim
On Apr 29, 2023, at 11:06 AM, John Woodgate
< jmw@...>
wrote:
Many types of transformer do not
need complicated models like Gummel-Poon for
transistors, but of course complicated models
like Chan can give more accurate results (often
more accurate than is necessary, but that also
apples to transistor models, which do not
account for variations between samples). Simple
models can use easily measured or calculated
parameters, so it is easy to relate the model to
the hardware.
Please note the new Subject line.
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
Rayleigh, Essex UK
I hear, and I forget. I see, and I remember. I do,
and I understand. Xunzi (340 - 245 BC)
On 2023-04-29 18:02, Jim
Wagner wrote:
For me. the real transformer challenge is
associating the physical parameters (dimensions,
numbers of turns, core material, and such) into
model parameters. One might reasonably assert that
this is no different than, say, transistors. There
is a big difference, though; I can build a
transformer but I am not likely to build a
transistor. I do not have the capability to measure
transistors sufficiently to create models, so must
rely on third-parties to do that. What third party
do I use for that ferrite toroid transformer that i
just built?
Perhaps the solution to this is a
transformer model generator (like VDMOS tool). I
can handle program writing but I do not know
enough about magnetics to even think about
something like that. To be useful, such a model
generator should rely on measurements the most of
us could do in a modestly equipped lab (say, with
a signal generator and an oscilloscope).?
Jim Wagner
Oregon Research Electronics
Susan wrote, "My big
issue/stumbling-block when using 'spice
simulators is transformer models; they all
seem to be described in intractable terms
making it difficult to translate something I
have in my hand to an accurate simulation
model."
That sounds like a topic for a separate
subject (not this one).? The simplest
transformer models are very simple.? It's
the more complicated ones that can be
challenging.
Andy
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Re: Is there a way to make node numbers appear on LTSpice schematics?
On 19/07/2023 15:16, Tony Casey wrote:
Functions
defined in the schematic cannot be used in the waveform viewer.
Similarly, parameters cannot be used either, unless they are
stepped, then they can be accessed through the same syntax as in
the schematic, by wrapping them in braces.
Although wrapping parameters in braces works, it's actually not
necessary - NF(Rsrc) works as well as NF({Rsrc}), in my example. I
guess this is because Rsrc appears in the list of waveforms
available to plot.
--
Regards,
Tony
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Re: Is there a way to make node numbers appear on LTSpice schematics?
On 19/07/2023 12:25, Andy I wrote:
marcel asked, "Is it possible to use parameters and functions defined on the schematic (not in plot.defs) in the waveform viewer?"
I do not believe you can.? If there is some ability to do that, it
is limited.
Functions defined in the schematic cannot be used in the waveform
viewer. Similarly, parameters cannot be used either, unless they are
stepped, then they can be accessed through the same syntax as in the
schematic, by wrapping them in braces.
In addition, special parameters and constants that the waveform
viewer understands, like Freq(uency), Omega, Q and K are not
understood in the schematic. Pi is an exception, but not E (Euler's
number).
I almost never use a plot.defs file.? At some point I had one, but
then I realized that the whole point of plot.defs is to make one's
LTspice work differently than everyone else's, which is something
I did not want to do.? But that's me.
If they (ADI?) changed how or when the plot.defs file was read
(e.g., when making a plot vs. only when starting LTspice, or
reading it again when saving it), it might have been an
inadvertent change that they thought didn't need an announcement.?
That is, if it changed at all.? It's also possible that it always
behaved this way, and nobody noticed or cared since so few people
use a plot.defs file.? Since you guys have more experience with
plot.defs files, I guess you would know if it changed.
Also I think it would make sense that LTspice knows immediately
about changes that you make to the plot.defs file, if you made
them from within LTspice's plot.defs editor (via the "Edit
Plot.Defs File" tool).? But if you edit your plot.defs with an
external editor, LTspice would not know about it unless it opens
the file again.? That is consistent with editing the standard.xxx
files -- LTspice knows the changes if you made them from within
LTspice's editor and you don't need to restart LTspice.? But if
edited in an external editor, LTspice doesn't know until it is
restarted.
LTspice definitely used to only read plot.defs when it was started,
and changes were not active until LTspice was restarted. This is
also true for library folders. If you add a folder (outside of
LTspice) in LTspice's library tree while LTspice is running, it is
also not available until after a restart.
I just checked again with 17.1.9, and found that you still have
restart LTspice for changes in plot.defs to be available. I could
have sworn that you now didn't, so my earlier comment doesn't stand.
The other thing I have found is that if you edit plot.defs within
LTspice when the waveform viewer contains a trace that uses one of
its function, LTspice reliably crashes. If you delete the offending
trace before editing, it doesn't crash. This is while using Wine. It
might be different in Windows. The behaviour is the same for 17.0.36
and 17.1.9.
Perhaps someone can check this behaviour in Windows, before I submit
a bug report?
--
Regards,
Tony
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FlightRisk
John Woodgate
Bell, Dave
Tony Casey