# Varying inductance

Discussion in 'General Electronics Discussion' started by Andrea1089, Nov 8, 2017.

1. ### Andrea1089

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Sep 13, 2017
Hi everybody,
I'm trying to modelize the behaviour of a ferrite with LTspice (see attachment).
The problem is that, basing on the datasheet, its impedance is frequency-dependent (see the maximum curve in the image attached).
So far, I think a good idea is to consider that it has just an inductive behaviour. In particular, I'd like to take into account the variation in its gradient at around 700 kHz (as if the inductance switches from 7 uH to 1.3 uH).
How can I do that in LTspice?

Actually, after testing the ferrite performance with LTspice, I'll have to import its model in Simetrix, so I fear a frequency-varying inductor is not a good solution.

Thank you,
Andrea

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2. ### Harald KappModeratorModerator

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Nov 17, 2011
SPICE is a time based simulator, it cannot, to the best of my knowledge, model frequency dependend behaviour.
You can model the impedance by using parasitic R and C elements or even a two-stage model as described here.

3. ### OBW0549

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Jul 5, 2016
SPICE does both time-domain simulation (the .TRAN analysis) and frequency-domain simulation (the .AC analysis).

4. ### Harald KappModeratorModerator

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Nov 17, 2011
Right, I forgot about that - I rarely use it. For the .AC analysis the circuit is linearized around the operating point and only small signals are used to stimulate the circuit within the limits of the linear approximation.
However, as far as I know there is no way of defining a frequency dependent component in terms of a function of frequency. The simulation is done in terms of currents and voltages as a function of time.

5. ### Andrea1089

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Sep 13, 2017
Fyi. I found the Glaplace function in LTspice. It performes what I'm looking for which, in this case, is a variation in the inductance of my ferrite. C and R should be neglected, actually.
The problem now is how to transfer all this in Simetrix/Simplis. I''m gonna have a look at its functions.

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11,522
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Nov 17, 2011
Nice twist