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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 |
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 |
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 |
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 |
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 |
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. |
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... ? |
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 |
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 |
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. |
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 |
Re: Ohms/volt? (was: Spark gap physics.)
开云体育Ohms being Volts per Ampere, Ohms per Volts would resolve as
1/Ampere. Le 20/07/2023 à 09:29, John Woodgate a
écrit?:
|
Re: Ohms/volt? (was: Spark gap physics.)
开云体育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? |
Re: Ohms/volt? (was: Spark gap physics.)
开云体育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. ? From: [email protected] <[email protected]> On Behalf Of
Richard Andrews via groups.io
Sent: Wednesday, July 19, 2023 9:16 PM To: [email protected] Subject: EXTERNAL: Re: [LTspice] Spark gap physics. ? Is there such a thing as x ohms/volt? |
Re: Transformer models WAS: New Simulator Written by Mike Engelhardt
#Transformer
开云体育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:
|
Re: Is there a way to make node numbers appear on LTSpice schematics?
开云体育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 |
Re: Is there a way to make node numbers appear on LTSpice schematics?
开云体育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?"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). 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 |