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    Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    Dear all,

    I am trying to simulate a Non-Linear capacitor in LTSpice whose voltage is a non-linear function of the charge across it. Please find the schematic attached below. However, I am getting Time step too small; initial timepoint: trouble with node "v_a" error. Can you please help me in fixing this? I tried changing the engine to Alternate in Control Panel but the error still persists.

    Also, is there any other way by which I can model a capacitor whose voltage is a non-linear function of the charge across it? My aim is to use such a non-linear capacitor in series with an ordinary capacitor and study the transient response.

    Regards,
    Raghu

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  2. #2
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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    This may happen because you set both capacitors to femtofarad size. Guess that's not intended.



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  3. #3
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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    Thats intended. The design specs give capacitors in the range of femto farads.



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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    May be true for C2, but you have set C1 to 1 femtofarad, too.



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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    1F is parallel to 1GOhm.. Simulators don't like these kind of absurd values and connections.



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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    If your C-V function is normal-ish then a MOScap, varactor or
    even a dumb diode model with the forward parameters "killed"
    could do what you want. Especially if the nonlinear capacitor
    in question is such a structure.

    Ideal elements seem like they're not troublemakers but the
    reciprocal of ideal is sometimes "ka-blooey".



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    Re: Non-LInear Capacitor SImulation - Time step too small error - LTSpice

    Besides the most likely unwanted femtofarad value of C1, there seems to be an error of reasoning involved with the design. Voltage source E1 is shorting C2, whatever it's value is, it has no effect on the circuit behavior.

    If would be more reasonable if you specify the intended capacitance function, so that people can suggest an alternative implementation.



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