How to make a capacitance variable with voltage in LTpice?

The value of a parameter must be known before the simulation begins. A parameter can be .step'ped, but each step is a new simulation. You may find some happiness in defining a capacitor in terms of charge. Check the LTspice Help file.

If you want a real part there are a couple of "Varicap" diodes in the library > diode> type>Varactor.

All diodes have max capacitance at 0V and decrease with reverse voltage in a logarithmic fashion. Varactor diodes are more precisely controlled for this attribute and specified by the C ratio and value at two voltages.

A high resistor value is used for biasing and large C is used in series when used to block the DC.

Generally the bigger the current rating or smaller Rs, or bigger power rating, the bigger the C(0V) capacitance.

Flyback said:

Hi,
How to make a capacitance variable with voltage in LTpice?

You presumably do a .param {capacitance} = (V(aaa) - V(bbb)) * 10nF
?
But that doesnt work

Click to expand...

Specify Q=10n*X for the value attribute