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I hope you're doing well ?

Thanks you so much for your help, indeed it works on my side too with "startup" option.

How did you find that ? It's almost magic for me :)

However, I didn't try yet with PULSE(0 13 0 100u 0 1 2 1)

I tried with another PTC model and it does the "singular matrix" error again.

But it was worth a try !

Thanks you so much, I keep on :)

The clue was that LTspice always failed to find the initial solution, i.e. the matrix state at time=0, rather than failure mid-way through the analysis, which is what happens in some problems.

From the point of view of this schematic, the difference is that with the "startup" switch, all DC voltage sources start at 0 and ramp up over the initial 20μs just like a real power supply (well, much faster, really), whereas if you use a "virtual" startup condition by using a pulse specification, you can do this one DC source at a time. Obviously, "startup" is much simpler to do.

I don't know where the exact problem was, since you say that all parts tested OK on their own. Sometimes the solution to a problem is more important than a complete understanding of the problem itself.? ;-)

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Regards,
Tony