Electronics > KiCad

how does Kicad simulation compare to LTspice?

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JohnG:
I have evaluated a number of free Spice tools, primarily for detailed simulation of switch-mode power converters. What I mean by detailed is the use of Spice to model both switching transitions with a lot of parastics, power transistors with highly non-linear capacitances, tiny parasitic inductances, etc. It's tough on a lot of simulators due to many vendors dubious ways of making non-linear caps in their models, and the need to have time constants that are orders of magnitude different in the same circuit.

LTspice and NGspice top the list. We chose LTspice for the following reasons:
*Best convergence and speed with the circuits and models we use.
*Usable (if somewhat clunky) GUI: this is required to get younger engineers started quickly, and for quick analyses. Schematics are pretty much necessary for collaboration and discussion, which we do a lot of amongst ourselves and with customers.
*Runs many third-party models with little or no change.
*Handles long simulations with large output files usably quickly and without frequent crashing.
*Appears to be around for a while
*Ability to run more sophisticated analyses using Octave or Python as a scripting engine. You can do optimization and MC and it works.

NGspice looks really promising, but it balked on some of the models we use, whereas LTspice converged properly to the best of our knowledge. And, the KiCAD GUI for NGspice is not there yet, and to be fair, it is not the main focus of KiCAD. But, what I really like about NGSpice:
*Runs many third-party models with little or no change.
*Open source
*Keeps getting better and more powerful
*Pretty good convergence (but not as good as LTspice)
*Handles long simulations with large output files usably quickly and without frequent crashing.
*Appears to be around for a while
*Ability to run more sophisticated analyses using Octave or Python as a scripting engine. You can do optimization and MC and it works.

I really wanted to like Microcap 12. It looks like the complete package, with extensive models, fantastic analytical tools, etc. But, in the end, we did not go with it for the following reasons:
*Not under development, and may quit running under some future OS. If it ever goes open source so that this situation is changed, I might look at it again. I've multiple times in my career had software tools that became unusable for one reason or another, with no hope of recovering the work lost. It really sucks when that happens.
*GUI so cluttered that I cannot find anything easily. I think you can simplify it via the preferences, but I don't want to invest time in something that's not supported.
*It crashed a lot on me running long simulations.

Just my $0.02,
John

PKTKS:

One more vote to ucap

alas in urge need of maintainers..

Paul

hvogt:
You may use KiCad/Eeschema for schematic entry, use the internal ngspice and then again Eeschema for plotting. Unfortunately the Eeschema/ngspice interface is currently still rather limited. However, lots of planning is going on to improve it.

ngspice has its own scripting language (or control language, formerly know as nutmeg, but vastly improved and enhanced).

You now may use Eeschema again for entering the circuit, but run the simulation in plain ngspice, using its control language. Now all ngspice options are available. Writing result data to a file or plotting is also done by ngspice (internal graphics, Postscript, SVG, or Gnuplot, all with UNICODE support). For a simple example please see the Eeschema/ngspice tutorial at http://ngspice.sourceforge.net/ngspice-eeschema.html#external.

Indeed models are not distributed with Eeschema/ngspice, but many are available at http://ngspice.sourceforge.net/modelparams.html and its associated links.

hvogt:
There are several examples for simulating audio circuits available here: https://forum.kicad.info/t/simulation-examples-for-kicad-eeschema-ngspice/34443.

Schematic entry has been done by KiCad/Eeschema 6.0.2, simulation by (integrated and/or external) ngspice-36.

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