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