I’m a newbie to KiCad and migrated from LT Spice and Micro-Cap. After a few hours making errors (!) I’ve been able to run some useful simulations. However, my confidence has been shaken by situations such as these:
adding an unconnected component e.g. resistor to the schematic changes the simulation results significantly.
I can reduce op amp supply voltages down to millivolts yet simulations still run as if the full supply was present.
Am I expecting too much, or missing something?
Thanks for any help.
Before I started to read KiCad forum I didn’t know people are using simulation so often.
If floating/unconnected component changes circuit simulation results I would expect it being a bug.
If not powered OpAmp works I would expect it being a result of OpAmp model used.
KiCad uses ngSpice for simulation, and that is a separate project, with it’s own website and development cycle. ngSpice is a quite usable simulator, but it does have it’s issues. I’m not exactly sure of it’s internals, but I guess it attempts to be “mathematically correct” instead of attempting to guess the intentions of users. So instead of simply ignoring an unconnected resistor, it may throw an error message. Another problem is availability of spice models. An electronics simulator can only be as good as it’s models, and a lot of models that LT Spice uses are either encrypted, not available at all, use proprietary extensions, etc. You can also find lots of spice models that do work with ngSpice, but their license is not compatible with Open Source stuff, and therefore they are not delivered as built in libraries. It’s not difficult to find them, or add them to KiCad symbols yourself, but it’s still a bit of a nuisance. the ngSpice website has a tutorial section for working with it in KiCad.