Transformer with 3 secondaries

[r061]

I am a ngspice newbie.

I am creating a transformer with a primary and 3 secondary windings. Using the subckt below, I do avoid the Not Positive Definite error with the specific coupling factors shown, found just by trial and error.

Here is an example of the error message, the SUBCKT at the end of this post avoids the error.

The Inductive System consisting of
l.xt1.l1 l.xt1.l2 l.xt1.l3 l.xt1.l4
k.xt1.k12 k.xt1.k13 k.xt1.k41 k.xt1.k23 k.xt1.k24 k.xt1.k34
is not positive definite

How can I specify a 3 secondary transformer with coefficients with good coupling ? I have read about Positive Define being a subject of linear algebra.

But in the context of ngspice, is there some practical and functional way to specify a transformer like this with closer to ideal coupling ? I had no problem creating a dual secondary.

I have the real transformer. I wonder if I created a model with all the parasitics, would that avoid the not positive definite error ?

.SUBCKT Trans_4 1 2 3 4 5 6 7 8
L1 1 2 10H
L2 3 4 10H
L3 5 6 3H
L4 7 8 3H
K12 L1 L2 1
K13 L1 L3 0.75
K41 L1 L4 0.75
K23 L2 L3 0.75
K24 L2 L4 0.75
K34 L3 L4 0.75
.ENDS Trans_4

[r061]

I thought I had tried coupling constant of 1 before and it didn’t work, but setting all the coupling does work.

It is an ideal transformer.

.SUBCKT Trans_4 1 2 3 4 5 6 7 8
L1 1 2 10H
L2 3 4 10H
L3 5 6 3H
L4 7 8 3H
K12 L1 L2 1
K13 L1 L3 1
K41 L1 L4 1
K23 L2 L3 1
K24 L2 L4 1
K34 L3 L4 1
.ENDS Trans_4