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# [SOLVED]Simulate Thermistors and Chokes in SIMetrix

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#### kkeeley

##### Member level 3
Hi,

I'm new to this board and have been reading some very interesting posts from other people, and I have found some great information.

I have just started work on designing a SMPS for a project that I have been working on for some years, and due to the complex nature and dangers of SMPS's I wish to simulate as much of the design as possible before physically build anything. I have some old PC power supplies that I was thinking of using for donors parts (Transformers, Chokes, etc). I have just started using SIMetrix and am finding it very easy to learn and use, I am now at a point where I wish to start using/creating more complex parts, like thermistors, transformers and chokes.

So my question is how do I create each of these parts, I have seen some where an example creating a sub circuit for a transformer, but I can't remember where.

Kenneth

I have used the following model of a transformer in the past. This is the spice for it. Basically on primary it is a "voltage dependant current source" with magnetizing inductance in parallel. And on secondary it is "voltage controlled voltage source".

**********************************************************
* MODEL: transformer
* Application: transformer model suitable for averaged
* circuit models
* Limitations: no losses, no leakages, two windings
**********************************************************
* Parameters:
* Lm=primary (magnetizing) inductance
* n=transformer turns ratio 1:n (primary:secondary)
**********************************************************
* Nodes:
* 1: primary-dot
* 2: primary-undot
* 3: secondary-dot
* 4: secondary-undot
**********************************************************
.subckt transformer 1 2 3 4
+params: Lm=250e-6 n=0.5
Lm 1 2 {Lm}
Gp 2 1 value={n*i(Es)}
Es 3 4 value={n*v(1,2)}
.ends
**********************************************************

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