ngspice — The Complete Guide: The Open-Source SPICE Simulator, Including Inside KiCad

ngspice is an open-source SPICE simulator, the successor of Berkeley SPICE. You may already have used it without knowing: it is the engine that runs simulation inside KiCad and in the Qucs-S interface.

Ngspice

Ngspice Project

Open-source SPICE simulator — DC, AC, transient and noise. The engine behind KiCad simulation.

Get it from the vendor

What it can do

Standard analyses — DC, AC, transient, noise, distortion and sensitivity.
Mixed-signal circuits — analog and digital parts together (XSPICE), including Verilog co-simulation.
Manufacturer models — loads standard SPICE models of transistors, op-amps and controllers.
Scripting — batch runs and Python integration for parameter sweeps.

How to use it

The convenient route is from KiCad: draw a schematic, add sources and models, and open the simulation window. If you prefer a dedicated interface, use Qucs-S. You can also run it from the command line with a netlist file.

ngspice or LTspice?

LTspice is especially fast for switching power supplies and comes with a rich component library, but it is not open source. ngspice is open, integrates with KiCad and runs on every operating system. For very large circuits or parallel computing — Xyce.