# Create Variable Inductance in SPICE

• akhurash
In summary, the conversation discusses creating a variable inductor in SPICE, particularly in NI Multisim. The individual is seeking help in creating a saturable inductor using a virtual inductor with a function in Multisim, but has not been successful. The conversation also mentions using a polynomial voltage controlled current source in parallel with L0 to create the variable inductor, and suggests referencing a PDF for more information.
akhurash
I'm trying to create a variable inductance in SPICE, specifically in NI Multisim. What I'm trying to do is create a saturable inductor. I need an inductor that changes it's inductance with current. Multisim does have a "virtual" inductor that you can create a inductance function with but I can't really get it to work and I used NI but their help isn't that great either.

Has any created a variable inductor or a saturable inductor in some sort of a SPICE program (or Multisim)?

Any help is greatly appreicated. Thanks!

It's pretty easy. You just put a polynomial voltage controlled current source in parallel with the L0.

The trick is, what do you set the coefficients to. If you're trying to match an actual particular inductor, you're probably going to have to measure and curve fit it.

See page 2 of this PDF.
http://www.intusoft.com/articles/inductor.pdf

## 1. How do I define a variable inductance in SPICE?

In SPICE, variables can be defined using the ".param" command followed by an equal sign and the desired value. For example, ".param L = 0.5" would define a variable inductance named "L" with a value of 0.5.

## 2. Can I use a mathematical expression to define a variable inductance in SPICE?

Yes, SPICE allows for the use of mathematical expressions when defining variables. For example, ".param L = 5 * (R1 + R2)" would define a variable inductance named "L" with a value equal to 5 times the sum of resistors R1 and R2.

## 3. How do I use a variable inductance in my SPICE circuit?

To use a variable inductance in your SPICE circuit, simply replace the numerical value of the inductor with the defined variable name. For example, if you defined a variable inductance named "L" with a value of 0.5, you would use "L" instead of "0.5" in your circuit.

## 4. Can I change the value of a variable inductance during simulation in SPICE?

Yes, you can change the value of a variable inductance during simulation in SPICE. This can be done by using the ".step" command, which allows for the sweeping of a variable's value over a specified range or by using the ".alter" command to change the value of a variable at a specific point in the simulation.

## 5. Are there any limitations to using variable inductances in SPICE?

While there are no specific limitations to using variable inductances in SPICE, it is important to note that they may affect simulation accuracy and may be more computationally intensive compared to using fixed inductances. It is important to carefully consider the use of variable inductances and their impact on simulation results.

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