I do not understand why when switching frequency (Fsw) is between 100kHz and 200kHz qspice simulation throw me this timestep too small error, and how to resolve it. It should be like that?
Resonant frequency of this circuit is:
1/(2pisqrt(1uH*1uF)) = 159.155kHz
Fsw=110kHz:
Plot looks pretty good, but simulation runs only till ~1.3ms (this is whem fatal error: timestep too small is occuring), but simulation should run till 30ms.
Is still this (by putting in parallel a 1nF/1pF cap at each switch and at bridge rectifier diode (right)) approach the right approach in order to avoid this timestep to small error in this case of circuits?
Timestep too small during .tran, normally represent convergence failure in numerical calculation, where result may oscillating or not within error limit.
abstol : Absolute current error tolerance
vntol : Absolute voltage error tolerance
cshunt : Capacitance added from every node to ground
In your example, your circuit can convert with one of this .option (if nothing change in your schematic)
.option cshunt=1p
OR .option vntol=5e-1 (with fast math disable)
Adding capacitance allows the simulation to converge by providing a ground path for high-frequency oscillations or numerical noise.
Reducing vntol (I do not recommend this, 5e-1 is quite large) allows for more error in determining a converged result.
abstol seems not critical in your example, but again, this is to allow more error in current and help converge
Read this Hspice user guide, section 14, title : Troubleshooting ‘Time step Too Small’ Errors. It explains several common approach in handling timestep too small in spice simulation. HSPICE User Guide: Simulation and Analysis (ucsd.edu)
You can also run your circuit without extra .option or capacitance, but by smoothing diode I-V curve with epsilon, e.g. .model D D Ron=1m Roff=100Meg VFWD=0.7 epsilon=0.1
Mike hosted a Webinar on 5-Sept-2024, where he explained how SPICE solves circuits and the key aspects you need to know to help your circuit converge. By reviewing this explanation, you will understand why adding capacitance across your switch/diode will be beneficial.
