Hi,
i currently attend a Powerelectronics course as Part of my Bachelor-Studies.
We did some basic Simulations of a Step-Down Converter in LT-Spice.
When i tried to replicate this Simulation in KiCad with ngspice i noticed some unexpected curves.
The current through the Transistor and the Diode seems to oscillate heavily.
The Oscillation seems to depend on the timestep(tstep) of the transient simulation in matters of amplitude and frequency.
When i chose a timestep of 50ns at a 50ms simulation window the oscillation fades out noticable.
On a timestep of 10^-4 of the simulation window like in one of the KiCad-Examples the oscillation stays large until the end of the 5ms switchmode halfperiod.
Just when i set the optional tmax to a amount of about tstep/10^2 or tstep/10^3 the results lock more simmilar to what i expected.
When i changed the models of the diode and the n-fet from the manufacturer-provided models to the ng-spice standard models the oscillation was also noticable but not that heavy.
(I also did a short test in Qspice to validate the LT-Spice result.)
Can someone please help me here or explain what is going on?
(My bad? wrong simulation settings?)
Thanks!
Step-Down_06.11.2024.zip (608.1 KB)
