Where is JFET footprint?

I am trying to layout an analog circuit which has a JFET. I have been able to find footprints for most of the other components but I cannot find a footprint for a JFET. In fact I see no footprints for any kind of transistor. Am I missing the obvious here? I could just make a new footprint but I just can’t believe that the footprint library does not have transistors.

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That is exactly what I would do.

What is the part number of the JFET that you are planning on using?

ON EDIT: Also, you did not indicate if the part is THT or SMD; that alone will affect which KiCad Footprint library to use.

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Thanks for replying. It is a 2N4221.

And now I have to ask, “What package it is in”?

Oh right. It is a THT. My whole project is THT.

The package is TO-72-4, but I am only using 3 leads.

Is it a small metal can case, or TO-3?

Note: I want to help as much as I can. Posts are short simply to save me time.

What are your plans for the 4th lead?

And, what KiCad schematic symbol did you use?

Note: All of these details matter.

It is a small metal can case

I just cut the 4th lead off since it is connected to the metal case and I don’t need that. I just used the KiCad symbol for Q/ n channel JFET.

@montelee

One issue that bit me was that different packages have different pin numbering. The screen grab shows that DGS is different than SGD; the sequence being 123 for both parts. I can now give you the correct Footprint for the part you have, but I do not know that you used the correct symbol.

ON EDIT:

The pin numbers for the device inputs/ouputs can be quite different dependent upon the package of the device. My library includes all the possible combinations, although not evey combination may be currently manufactured; never say never.

Yeah neither do I. I mean, I don’t know if I used the correct DSG or SGD. I should look up the pin layout for this, yes?

Understood. I knew the pin configuration when I built the prototype on an experimenter PC board, and now I want to make several devices using this circuit and so I am learning KiCad specifically for this project. This is my first KiCad project.

Yes!

Sometimes the pin numbers are different for the Gate (for example). I will look up both the TO-72-4 and TO-3 packages and check the pin/pad numbers. They might be the same in this instance; they are not always the same.

I will look up the exact pin configuration and see if it matches the symbol I have used. If not I will either choose another or make my own. But that still leaves the footprint. Maybe it will be easier to just make a new footprint. I’ve aleady done that for some large film capacitors I am using.

Great conversation!

I need a bit more time to work through the possibilites; Google gave conflicting results.

Okay. Thanks for all your help. This forum is pretty cool. I have some unrelated stuff to do now, but I will check back later.

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Interesting…

Google, so far, gives:
1/ Source, 2/ Drain, 3/ Gate & 4/ Case,
BUT my trusty old D.A.T.A books, printed on paper and pre-dating the internet give 1/ Drain, 2/ Source, 3/ Gate & 4/ Case. :thinking:

EDIT:
@montelee
The numbers attached to the pin names match @paulvdh’s posted footprint below.
It does’t help much with pins one and two though.

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I’t think you (at least started with) some wrong assumptions.

In KiCad there is no such thing as “a footprint for a JFET”.
There are schematic symbols for JFets, but footprints are (at least partially) separate from footprints. Footprints are made for the PCB parts.

TO-72 is a quite old package, and indeed has 4 pins.
https://duckduckgo.com/?q=TO72&t=hx&va=g&iax=images&ia=images
And KiCad can’t know if you cut of some pins.
So the simlest is to just use Package_TO_SOT_THT/TO-72-4, and then leave one hole open on the PCB (or solder the pin you cut off back in)
(I know you already found it, but you still get a screenshot for free)

I would not create a new footprint from scratch. It’s much quicker to just copy an existing footprint to your own library (KiCad’s are read-only) and then edit it. Even a footprint from a somewhat similar package such as TO-92 can be copied and easily modified to fit your transistor.

@montelee

Or bend the leads on your TO72 package, which is probably easier, or use a TO18, which is the three pin version of a TO72… that will more suit your transistor with the amputated leg.

Still doesn’t solve the problem of the Source and Drain, though. :slightly_frowning_face: