Transformer KiCAD symbol

I have managed to create the schematic very nicely but i have problem with the symbols of the transformer. The kind of transformer that ma finding on Digikey shop has different symbol compared to what we have on KiCAD. What should i do in order to have a uniform symbol?

What is your idea of a

Schematic symbols are just some simple graphics and attachment points for wires to map those connections to footprints.

There are also many different types of transformers. From small signal isolation transformers to big power transformers EI core transformers, toroidal transformers and many more. Why would schematic symbols have to look “uniform”?

The only important part is that it is recognizable as a transformer in the schematic (correct number of windings to understand the meaning of it all) and that the pins of the schematic symbol match with the footprint.

KiCad itself only has a few generic transformer symbols. If the digikey libs have matching sets of schematic symbols and footprints, then use those, but always carefully verify whatever data you use. Small mistakes can lead to lots of magic smoke escaping.

Just make sure you don’t end up with this kind of transformer. :rofl:

My friend who sells toys at a market says that they transform 1.5V batteries to 0V ones, to the chagrin of parents.


Just make your own.
Go into your symbol editor, “save as” an existing Kicad transformer into your personal library, explore the tools on the RHS,
and transform that transformer to the transformer required using those transformation tools in transitional steps. :slightly_smiling_face:

Wire you saying this? Sounds like one good turn deserves another.

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I’m out of breath now. Good one. :+1:

Ain’t no such thing as a uniform symbol for a transformer. They’re all different.
Make an own library and copy one of transformers from the standard library there and modify it.
The “TRANSFx” or “TEZxxx” symbols would be the best basis for your own symbols.

Indeed. Transformers are almost always custom. This is a symbol for one which I wound for myself using a PQ20/20 bobbin and ferrite core set. (Strictly speaking it is a coupled inductor rather than a transformer, but that is another discussion.)

just being curious: what are the purple “not connected” connections for?

They’d be unused pins on the bobbin, or bad turns that didn’t deserve another turn… see:


Sometimes the transformer manufacturer uses a standard winding bobbin with more pins than needed. Transformers are frequently made as custom parts


As I understand it, that is the “correct” (??) way to deal with pins that are not supposed to be connected. I think that any schematic connection would probably cause a DRC error. In this case I made the transformer, so I know that if I connected it to a net it would have no effect on circuit operation. I invite comments, either serious or (not so much) on this.

There are some ICs which have “not connected” pins and I am not entirely sure what would happen if that pin were connected to a net. Sometimes connecting it to a net would seem to be convenient.


On looking at my own symbol, I note that pins 12 and 9 are not shown as “not connected” but I did not connect them. This symbol is somewhat general and somewhat specific. :grimacing:

The pin locations on a transformer can be important relative to the transformer construction. (You sort of have to make one or two transformers in order to best appreciate this. Transformer design requires theory of course, but some of the details are very “hands on” matters) So in general, pins 2,3,4,5 and 9,10,11,12 are the ones which I deem better suited for my use on the standard bobbin. In this particular design I have only 3 windings and I did not use pins 9 and 12.

Great minds think alike!
I always include the unused pins of transformers in schematics.

These days (hobby only) I wind my own. I’ll start with symbols (way up top examples), then, when the board is laid out, I’ll decide the most convenient and suitable pins to which I will attach the windings, after which I will re-annotate the pins on the symbol to match the footprint.

What about grated minds? (See The Silence of the Lambs (film) - Wikipedia) Well…not exactly.

Yes I think showing the unused pins makes for better documentation. I easily forget what I did a month ago… :frowning:

My memory isn’t what it used to be.

Also, my memory isn’t what it used to be.


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