SPICE Transformer Model Spreadsheet

[Robert McLean]

Some time ago I posted a spreadsheet for generating the parameters for a transformer SPICE model. I have received some recent emails asking questions about it, and I have also seen the recent post from pweaudiotech with his spreadsheets. This has jogged my memory and made me remember that I made a much improved version over a year ago.

It generates the SPICE model as well a just the parameters.
It will generate models for single ended, push pull, ultralinear, with or without multiple speaker taps.

Use is simple, instructions are included on the first sheet of the spreadsheet.

Attached is a screen shot showing the simplest case, a SE transformer with a single output. The xls file (zipped) is also attached.

The usual caveats apply :
This is a model, reality will be slightly different.
It does not model core effects ie saturation etc.

The parameters I have listed for various transformers may or may not be accurate, I have taken them from data sheets, from websites, from wherever, and in some cases where information was not available, just guessed. So put whatever numbers you think best in here.
Also, in some cases I have added multiple speaker taps to transformers that dont really have them, just to play around with them.

[joseangel]

Thank you very much for this interesting and helpful model.

Best regards,
Jose Angel Jimenez

[jakruby]

sorry to sound foolish but how does one create the model in LTSpice?

[payloadde]

Originally Posted by jakruby

sorry to sound foolish but how does one create the model in LTSpice?

Transformer Models

How do I build a transformer model?

The best way would be to draft a model with coupled inductors
with a mutual inductance statement placed as a SPICE directive
on the schematic. See the section on mutual Inductance for more
information. Inductors participating in a mutual inductance
will be drawn with a phasing dot.

The following example demonstrates a transformer with 1:3 turns
ratio (one to nine inductance ratio) with a sine wave input and
simulates for 0.1ms. The K is set to 1 to model a transformer
with no leakage inductance.

see page 185 of the manual: http://ltspice.linear.com/software/scad3.pdf

[SemperFi]

Thanks man! Great work.
oh...

[jakruby]

sorry i understand how to define simple transformers as you have just posted but i meant how do i create the model to use with one of the transformers from robert maclean's spreadsheet. specifically how do i name the resistors 'Rp1' & inductors 'Ls1' etc to match the model text. i tried putting the value of the resistor as 'Rp1" but i get a "Can't find definition of model "RP1"" message.

[payloadde]

Why don't you just add a normal R in series with L and give it the value calculated from spreadsheet
or right-klick on L and fill in the calculated value of R as <Series Resistance>

[SemperFi]

Originally Posted by jakruby

sorry i understand how to define simple transformers as you have just posted but i meant how do i create the model to use with one of the transformers from robert maclean's spreadsheet. specifically how do i name the resistors 'Rp1' & inductors 'Ls1' etc to match the model text. i tried putting the value of the resistor as 'Rp1" but i get a "Can't find definition of model "RP1"" message.

I havent tried yet, but isn't it just to copy the blue text in the worksheet into a 'spice directive' and stick that into the schem?

[SemperFi]

hmmm...I just tried and I also have trouble getting it to work. I drew up an exact replica of the transformer schem, and inserted the spice directive, and get 'Rp1: Missing resistance value.'
Of course I could type all values in manually, but that kinda makes the spreadsheet useless doesn't it?

[gootee]

Originally Posted by jakruby

sorry i understand how to define simple transformers as you have just posted but i meant how do i create the model to use with one of the transformers from robert maclean's spreadsheet. specifically how do i name the resistors 'Rp1' & inductors 'Ls1' etc to match the model text. i tried putting the value of the resistor as 'Rp1" but i get a "Can't find definition of model "RP1"" message.

In LTSpice, you could use {Rp1} for the resistor's value and then have a .param spice directive to define Rp1, like .param Rp1=27.

There is a very good paper about modeling transformers, at :

http://www.onsemi.com/pub_link/Collateral/AN1679-D.PDF

Based on that paper, I made a spice model for a two-winding transformer for which you only need to insert simple measurements, and spice calculates the model parameters. It can be downloaded from here:

Spice Component and Circuit Modeling and Simulation