Hi All,
I'm trying to do a SPICE simulation of an AC-powered circuit, including varistors and a combined wave generator model to simulate the effects of a line surge.The problem is that placing the varistor in parallel to the AC voltage source will cause the simulation to crash (convergence problems). I have added some line source impedence also on the schematic. Doing some research on the web, I found out that usually MOVs are modelled in spice as current-controlled voltage sources. The relationship between voltage and current is quite complex and involves the logharitm of the current flowing in the varistor. If that is the case, than with an AC voltage source the current will reverse in the varistor, so that the math is no longer valid (the log argument cannot be negative). I was thinking of define a behavioral model for the varistor using the absolute value of the current flowing in the varistor instead of the current itself. Looking at some MOVs characteristic, the real behavior should be the same no matter the direction of the current. What do you think? Is there anyone who ran in the same problem? Thanks in advance for your help and Happy new year. Andrea.