Discussion in 'Electronic Design' started by Ira Rubinson, Jun 9, 2006.

1. ### Ira RubinsonGuest

Does anybody know how of a transformer that I can add to the component
library for Linear Technologies SwitcherCAD? I'm trying to simulate a
switching power supply.
Thanks -Ira

2. ### GenomeGuest

Without getting too wordy about things have a look at....

http://www.genomerics.org/smps/offconv/offline.html

For the general idea for an ideal transformer in SPICE.

You take that idea and then add 'parasitics' as required.

You might get leakage inductance by playing with the coupling coefficients
but it is easier to make them all 1 and then add series inductance to the
appropriate windings.

DNA

3. ### Fred BloggsGuest

I have never used SWCAD but do know it is optimized especially for
switchers. In a pinch, certainly you can find an ideal transformer, then
parallel it with an inductor equal to the magnetizing inductance, and in
series, with the whole assembly, add a combo of R+Ls where R is the
winding resistance and Ls is the leakage inductance, which can be taken
to be 1% of magnetizing inductance. Add a secondary series R+L as well.
This will give a first order approximation. For an exact simulation
SWCAD should have provisions for a Jiles-Atherton [sp?] transformer
simulation, mainly to simulate core losses, and this requires
information pertaining to core material and geometry- much more
detailed. You can also estimate the loss and represent this in the first
order model by a resistor Rm in parallel with the magnetizing
inductance, which is still useful for obtaining bounds.

4. ### martin griffithGuest

Think I found this on the yahoo gloops LTSpice

Lp N003 N004 Lp
Ls N005 N006 Ls
Llp N001 N003 Llp
Lls N005 N008 Lls
Rp N004 N002 Rp
Rs N006 N007 Rs
Cs N008 N007 Cs
Cp N001 N002 Cp
Rc N003 N004 R
K1 Lp Ls 1
..backanno
..end

martin

5. ### Fred BloggsGuest

Just another first order with no core loss or nonlinearity representation...

6. ### colinGuest

The easy part is you use an inductor for each winding then link them all
with the K directive.

This provides an ideal transformer, you can then model the losses wich are
frequency dependant with L/R/C circuits around the winding inductance, or
even use the parasitic parameters of the inductors.

Some inductors specify eqv circuits in their data sheets. I dont know about
transformers, especialy if you are winding your own, maybe there is a
normalised circuit equivalents for each type of magnetic material ?
obviously it would vary a lot depending on construction gap etc.

I supose you could even model the magnetic path in circuit terms, theres a