LTSpice: how to add a transformer?

Question

Hi there - I'm trying to add a transformer to a LTSpice schematic. Can anybody give me any suggestions as to how to go about doing this? I can't find them anywhere! I remember in one circuit simulation program I used years ago I had to couple two inductors to create a transformer, but I can't even find such an option in the inductor properties.

Thanks,

-Michael

Tom Bruhns · Accepted Answer

You can just place two inductances and something like "K1 L1 L2

0.999" (text) next to them (or anywhere on the schematic, it's more readable if it's close to the inductors involved). There are more complicated models, including capacitance and resistance, of course, and you can also create one using sources to emulate the coupling.

You should find at least a couple examples of transformers in the examples/educational directory under LTSpice: transformer.asc and transformer2.asc.

You'd do well to join the Yahoo group for LTSpice, where you will find examples of transformers, discussions about transformer models, and lots of helpful folk.

Cheers, Tom

Joel Kolstad · Answer

You add two inductors and then add a SPICE directive (Edit->SPICE directive) along the lines of, "K1 L1 L2 0.99" which says L1 and L2 make up a transformer with a coupling coefficient of 0.99. (And in case you don't recall: The turns ratio goes with the square root of inductance -- if L1 is 1mH and L2 is 4mH, L1 has "x" turns and L2 has "2x" turns.)

See the example: c:\\program files\\ltc\\swcadiii\\examples\\educational\\transformer.asc. For a three-winding transformer, there's transformer2.asc.

---Joel

LTSpice: how to add a transformer?

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