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Old 11th Jan 2017, 7:58 pm   #1
crackle
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Default 2N3819 Junction gate field-effect transistor (JFET)

Am I going mad or are these 2 diagrams of the pinouts of the 2N3819 contradictory.

Confused

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Title should have been 2N3819 Mosfet
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Old 11th Jan 2017, 8:36 pm   #2
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Default Re: 2n3819 Mosfet

Truth is, with quite a lot of such FETs the source and drain were interchangeable!
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Old 11th Jan 2017, 8:39 pm   #3
kalee20
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Default Re: 2n3819 Mosfet

It's a JFET, not a MOSFET!
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Old 11th Jan 2017, 8:44 pm   #4
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Default Re: 2n3819 Mosfet

It used to be conventional to give transistor pinouts looking up the leads from the bottom. I wonder if the 'top view' is the error here.
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Old 11th Jan 2017, 8:47 pm   #5
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Default Re: 2n3819 Mosfet

They are the same pin out. The first data sheet shows a photo with the flat at the top and the drain to the left. The second one shows a line drawing with the flat at the left and the drain at the bottom.
I have in the past seen and used some a far east clones in a plastic TO18 case. You would be much more confused if you found a TO18 one.
I always default to a view with the leads facing my eyes because with a top view the leads would be hidden.
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Old 11th Jan 2017, 8:51 pm   #6
TonyDuell
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Default Re: 2n3819 Mosfet

They are the same pinout if the second diagram is drawn looking on the wires (which was, as I said, conventional). But it says 'top view' under it, which to me means looking down on the non-wire side of the package.
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Old 11th Jan 2017, 9:02 pm   #7
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Default Re: 2n3819 Mosfet

It also shows the lead outlines dashed (for hidden) which fits with the top view statement.

Either the two manufacturers made them differently or one is wrong.
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Old 11th Jan 2017, 9:38 pm   #8
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Default Re: 2n3819 Mosfet

As Refugee points out, the pin-outs are identical - it's just the numbering the differs. If you rotate the second pic 90 degrees so that it's orientated as the first pic with the flat at the top, left to right it reads D, G. S, just as does the first pic, but one is numbers 1,2,3 - the other, 3,2,1.
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Old 11th Jan 2017, 10:11 pm   #9
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Default Re: 2n3819 Mosfet

Hi

They are actually different. The Vishay version shows the pin out viewed from the top of the transistor. I have come across this ambiguous situation before with JFETs particularly the 2N3819.

Regards
Symon.
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Old 11th Jan 2017, 10:19 pm   #10
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Default Re: 2n3819 Mosfet

I am not the only one confused then by these 2 spec sheets. It seems we have almost a 50:50 split as to if the drawings show the same thing, or if they are different.
I guess a 3rd and 4th drawing may help confirm which is correct.

Mike
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Old 11th Jan 2017, 10:24 pm   #11
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Default Re: 2n3819 Mosfet

It looks like Vishay have a typo on their data sheet , it should say "bottom view". Looking at the pin-outs from the bottom with the flat side facing upwards the drain is on the left, for the 2N3819 its D,G,S going left to right.
To make life awkward , this is different to the common garden MPF102 which is D,S,G.
It was probably a hang over from the days of vacuum tubes that many devices got specified by bottom view pin outs. However I always thought it interesting that nearly all logic IC's (74 series etc) all had top view pin outs.
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Old 11th Jan 2017, 10:38 pm   #12
Philips210
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Default Re: 2n3819 Mosfet

As G6Tanuki points out, the drain and source are interchangeable in many circuits.

Symon.
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Old 11th Jan 2017, 10:38 pm   #13
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Default Re: 2n3819 Mosfet

Yes, transistors by convention are drawn with pins facing upwards, but IC's with their pins facing downwards. The Vishay drawing is against convention!

The diagrams are actually opposite to each other, but the 2N3819 is a symmetric device, so source and drain can be interchanged. Some samples may work better one way round, some the other, in a particular circuit - but in manufacture, the geometry does not differentiate between source and drain.
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Old 11th Jan 2017, 11:05 pm   #14
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Default Re: 2N3819 Mosfet

Interesting conundrum! If you take it that the Vishay sheet correctly shows the 'Top View', then the pin numbers match up with the Fairchild sheet, but the pin assignments are reversed. If you assume its an error and the Vishay sheet shows the bottom view, then the pin assignments now match up but the pin numbers are reversed!

For my 2p worth, I would observe that if, as Wikipedia seems to suggest (https://en.wikipedia.org/wiki/TO-92), the standard pin numbering sequence on a TO-92 package is shown correctly on the 3D Fairchild illustration, then the Vishay sheet must indeed be showing the top view. This would seem to suggest that one of them has the pin assignments reversed. But which one is correct? Well one possible thing to do might be to compare spec sheets from other manufacturers:

http://www.onsemi.com/pub_link/Collateral/2N3819-D.PDF
http://www2.eng.cam.ac.uk/~dmh/ptialcd/jfet/2N3819.pdf

But just when you think you have the answer, you come across this one:

https://www.centralsemi.com/get_docu..._id=2n3819.PDF

In short, op, you are not going mad! There does seem to be an inconsistency in pin assignments between manufacturers. They all number the pins on the TO-92 package the same way, but some have drain on pin 1, others have source on pin 1. It is just as well, I guess, that it does not really matter, although a bit of consistency would have been nice!

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Old 11th Jan 2017, 11:55 pm   #15
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Default Re: 2N3819 Mosfet

I think with the pin number assignments for transistors & fets they are merely to reference the pin numbered in the individual diagram to a list on the same diagram and have no other meaning? Possibly this was due to the wide range of transistor packages. So the actual pin numbering could be quite different depending on the particular data sheet & manufacturer.

In the case of IC's though it was more regular with say the top view being standard, the notch on the IC on the left hand side and pin 1 always being the lower left terminal on the diagram and often a dot/indent near pin 1 on the package.
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Old 12th Jan 2017, 7:12 am   #16
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Default Re: 2N3819 Mosfet

Hi Waveydipole
So is that a fact the 2N3819 JFET can be used either way round, with equal efficiency, the only pin which needs to be specific is the gate.
Wow that does seem strange.

The project I am working on is a Minimod TX, Phil G4SPZ has been sent me a photo of one he made so I will be fitting the JFET in the same way.
The positive supply is fed to the JFET by the red and green wire.
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Last edited by crackle; 12th Jan 2017 at 7:27 am.
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Old 12th Jan 2017, 8:22 am   #17
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Default Re: 2n3819 Mosfet

Quote:
Originally Posted by kalee20 View Post
It's a JFET, not a MOSFET!
Yes sorry. I wonder if that could also be changed in the title.

Thanks
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Old 12th Jan 2017, 8:27 am   #18
Phil G4SPZ
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Default Re: 2N3819 Mosfet

I fitted mine as per the Fairchild diagram. I have made two MiniMods and they both work fine.
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Old 12th Jan 2017, 9:55 am   #19
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Default Re: 2N3819 Mosfet

MPF102's, 2N3819's, J310's and many similar can be used with Drain and Source interchanged without ill effect, only the Gate is specific.

It's a function of how they are constructed.

I've just drawn up a project that use the SMD version of the J310 and the datasheet specifically mentions that D & S can be reversed (which made the pcb layout much easier).

Terry

Last edited by Terry_VK5TM; 12th Jan 2017 at 9:57 am. Reason: more words
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Old 12th Jan 2017, 10:27 am   #20
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Default Re: 2N3819 Mosfet

I agree that Source and drain are interchangeable.

The 'Siliconix FET Design Catalog' 1982 shows the chip layout as completely symmetrical.

A point I had not noticed before is that two completely different chip layouts are given for the 2N3819!
One 'NP' is also used by the 2N4416 etc and the other, 'NRL' by the 2N3823 etc.

I can only assume that the specification of the 2N3819 is so wide that either chip will meet it and that they used whichever they had a surplus of.

Jim
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