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 ¨¤ 09:29, John Woodgate a
¨¦crit?:
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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Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
Actually inductance also varies with level. These are the "magic"
properties of iron cores. Basically, shaking the magnetic domains
is more difficult at the start of the magnetization curve (until
it reaches saturation), and more difficult as frequency increases.
There are models for simulation of the inductance vs. level (see
Chan modle), but I'm not aware of models for simulation of
inductance vs. frequency.
Maybe someone can chime in...?
toggle quoted message
Show quoted text
Jerry,
What causes a transformers inductance to decrease with
increasing frequency?
It sounds like my model of how audio transformers work is
too simple.
? --? Gavrik
The only issue I see with that is that it doesn't take
into account the fact taht inductance decreases as
frequency increases.
The ratio is typically 4:1 between 20Hz and 20kHz.
So using the LF inductance all along results in using a
too high coupling coefficient in order to agree with the
HF response.
I routinely use 2 or 3 different values of Lnom depending
on frequency.
For those who are interested in
modelling tube amplifiers and the output transformers
used:?I have a thread on DIYaudio? with easy to use
LTspice transformer models.
There are currently 3 flavours: Push-Pull with
ultra-linear taps, Ditto with extra cathode feedback
windings and Single-ended. I am working on a Hammond 125A.
Just enter the numbers from the transformer datasheet. All
tedious calculations are done by LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152
RS4=0.145 K=0.9999987] for an AMPLIMO Toroidal Output
Transformer type 20PP8K0S.
Comments are welcome,
Ite
|
Re: Using Q=expr syntax in capacitor
Hi Andy, thank you, it looks like the solution to the issue! :)
|
Re: Is there a way to make node numbers appear on LTSpice schematics?
On Tue, Jul 18, 2023 at 11:25 PM, Andy I wrote:
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.
You have the mind of an ADI engineer. Indeed, it does not work when using an external editor :--) -marcel
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Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
It depends how you measure
inductance. A real inductor has series resistance (copper
loss) and parallel resistance (iron loss).? You can measure in
two ways? - as a series RL network and as a parallel RL
network.? Neither gives you the true behaviour over a large
frequency range. You can model this in LTspice to see what
happens.
======================================================================================
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)
toggle quoted message
Show quoted text
Jerry,
What causes a transformers inductance to decrease with
increasing frequency?
It sounds like my model of how audio transformers work is
too simple.
? --? Gavrik
The only issue I see with that is that it doesn't take
into account the fact taht inductance decreases as
frequency increases.
The ratio is typically 4:1 between 20Hz and 20kHz.
So using the LF inductance all along results in using a
too high coupling coefficient in order to agree with the
HF response.
I routinely use 2 or 3 different values of Lnom depending
on frequency.
For those who are interested in
modelling tube amplifiers and the output transformers
used:?I have a thread on DIYaudio? with easy to use
LTspice transformer models.
There are currently 3 flavours: Push-Pull with
ultra-linear taps, Ditto with extra cathode feedback
windings and Single-ended. I am working on a Hammond 125A.
Just enter the numbers from the transformer datasheet. All
tedious calculations are done by LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152
RS4=0.145 K=0.9999987] for an AMPLIMO Toroidal Output
Transformer type 20PP8K0S.
Comments are welcome,
Ite
|
Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
Jerry,
What causes a transformers inductance to decrease with increasing frequency?
It sounds like my model of how audio transformers work is too simple.
? --? Gavrik
The only issue I see with that is that it doesn't take into
account the fact taht inductance decreases as frequency increases.
The ratio is typically 4:1 between 20Hz and 20kHz.
So using the LF inductance all along results in using a too high
coupling coefficient in order to agree with the HF response.
I routinely use 2 or 3 different values of Lnom depending on
frequency.
For those who are interested in modelling tube amplifiers and the
output transformers used:?I have a thread on DIYaudio? with easy
to use LTspice transformer models.
There are currently 3 flavours: Push-Pull with ultra-linear taps,
Ditto with extra cathode feedback windings and Single-ended. I am
working on a Hammond 125A. Just enter the numbers from the
transformer datasheet. All tedious calculations are done by
LTspice in the model.
Something like [Rpp=8k Lpp=1220 UL=35 Cp=390p Rp=152 RS4=0.145
K=0.9999987] for an AMPLIMO Toroidal Output Transformer type
20PP8K0S.
Comments are welcome,
Ite
|
John Woodgate
Bell, Dave
Tony Casey