Electronic – Why do circuit simulators like LTSpice prefer current sources instead of voltage sources

ltspicespice

I was having trouble with a "time step too small" error, and came across this post explaining that "stiff" equations gives LTSpice problems. Looking into LTSpice's documentation, they say that:

It can't be stressed enough that stiff voltage sources (especially
nonlinear behavioral types) are problematic because, unlike current
sources and/or resistors, they will not yield to capacitances at small
time steps during convergence difficulties in a transient analysis.

My question is, what is it about the way LTSpice solves circuits that makes pure voltage sources so hard to deal with? In school, EEs learn about node voltage and mesh current methods, so an answer relating to these methods would be appreciated.

Best Answer

That's because LTspice uses the modified nodal analysis, where currents are analyzed, together with conductances & co. Mike Engelhardt, the author of LTspice, said repeatedly that voltage sources, which have (machine) zero internal resistance, pose problems in the matrix solver due to the inversion of this zero resistance. That's not to say voltage sources are prohibited, just that current sources will be superior in terms of convergence.

What is learned in school and how a solver in implemented in software, can be two very different things. And what you're quoting there is not part of the official help, but an addendum from a very knowledgeable member of the LTspice group. But you can read more straight from Mike, himself, from this link.