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Need help determining orientation of FET package in drawing

Discussion in 'Audio' started by LearningSomethingToday, Mar 4, 2018.

  1. LearningSomethingToday

    LearningSomethingToday

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    Mar 4, 2018
    Can someone help me determine the which pins are Gate, Drain and Source for the dual FET? (shown with the large oval shape near the center of the image)
    I know the middle pin on either side is the Gate but how do I determine the Drain and Source from the symbol the way it is drawn?
    This device is supposed to be a 2SK333 N-Channel Differential Amp. Why did the designers go with the dual package? Is it a cost saving measure? Can the same thing be done with to individual FETs?

    I am looking to replace this component on a board that has them missing. The board has no indicator for determining orientation. I want to make sure I am not putting it in backwards.

    Thanks



    snip.jpg
     
  2. Bluejets

    Bluejets

    3,519
    714
    Oct 5, 2014
    Data sheet will show which pin is which.
    One would expect drain would be the top pins.
    Usual reason for common encasing is to match the device characterists more closely.
    Others will confirm positioning.
     
  3. LearningSomethingToday

    LearningSomethingToday

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    0
    Mar 4, 2018
    I have the datasheet and I can see which pin is D and S. There is a slant on the component case that helps the user determine orientation. The board that is receiving the part has no indication of pin 1. I can put it in one way or spin it 180 degrees and have the D & S for both sides in different positions. Did I make sense in my explanation?

    I have another question about this component. I watched videos on how to test a MOSFET with a meter. I cannot get these devices to follow that procedure. I don't get a short or open. I always get a small volatge drop. Maybe the devices are bad but they are supposed to be new. I am assuming it is just two fets in one case. Shouldn't I be able to test each side of the device as a separate fet?

    Sanyo SK333F.png
     
  4. Audioguru

    Audioguru

    2,618
    593
    Sep 24, 2016
    The FETs are junction Jfets, not Mosfets.
    Some Jfets are symmetrical so that the D and S can be swapped without changing the spec's.
     
  5. LearningSomethingToday

    LearningSomethingToday

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    Mar 4, 2018
    That's very interesting. Thanks for pointing out this was not MOS. If tested out of circuit, would it test like a mosfet? This may be the reason why testing with my meter is giving me unexpected results.
     
  6. Bluejets

    Bluejets

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    714
    Oct 5, 2014
    Was this a statement or a question?

    You have the data sheet.
    You have the drawings.
    You have the pcb.

    What more could you need?
     
  7. LearningSomethingToday

    LearningSomethingToday

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    Mar 4, 2018
    It is a question. Unless I am missing something unless the drawing or PCB calls out what pin should sit where there are two possibilities for the orientation of the package.

    Look at my drawings. They do not denote what is D or S.
    The silkscreen on the PCB does not designate pin "one" or anything for that matter. The six pin package can be installed in one of two ways. How do I determine the correct orientation of the 6 pin package, either 0 degrees rotated or 180 degrees rotated.

    From what I am looking at the only way to really determine which should be D or S is to understand the electrical flow presented in the diagram. I confess I do not know enough about how fets work to make a solid determination, which is why I am leaning on the expertise of others. I have assumed that the higher potential of +66 volts for the + rail would go to Drain. I can see a few example circuits that show just that all over the net. However when you throw in a equally negative rail of -60 volts then I start questioning myself.

    I just want to know if the D pins of the package should be pointing towards the top or bottom on the drawing.
    Thanks
     
  8. Bluejets

    Bluejets

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    Oct 5, 2014
    You know I could have sworn I answered that in post #2

     
  9. LearningSomethingToday

    LearningSomethingToday

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    Mar 4, 2018
    I did read that. I apologize; I did not realize that was a firm answer. It looked ambiguous when you said "expect". I have "expected" a lot of things to be one way only to let the smoke out of a transistor because it just was not. A great example is how I was working on an amp that had a wire ribbon numbers in the reverse order on one channel and not the other. My expectation and reality were two very different things. Luckily I caught that in time; dumb silkscreening by the vendor.

    I am placing the component in the circuit. Your answer helps me validate my initial guesses.
    Thanks for the help.
     
  10. Audioguru

    Audioguru

    2,618
    593
    Sep 24, 2016
    You must learn the details about FETs:
    1) A Jfet has an N and P junction and is "depletion" type that is turned on hard with no bias voltage and is pinched off when its gate-source has reverse bias.
    2) A Mosfet does not have a junction and is "enhancement" type that is turned on hard when its has bias and is pinched off with no bias voltage.

    Since the pcb is not marked which way around the IC should be mounted then try it one way and test the circuit to see if it is OK.
     
  11. 73's de Edd

    73's de Edd

    2,734
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    Aug 21, 2015
    Sir Learning something . . . . .else . . .today . . .


    Sure that case is marked. . . .SEE . . . . The inner sloped bevel / chamfer of ONE of the edges of the case, and the way that it relates to the terminals. You can see it from one illustrations profile, or they also are designating it with a dotted line from its nonviewable side.


    73's de Edd
    .....
     
    Last edited: Mar 5, 2018
  12. LearningSomethingToday

    LearningSomethingToday

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    0
    Mar 4, 2018
    I saw that bevel a long before I started this thread. I pointed that out in post #3. I knew the absolute orientation of the component itself...I have since figured out the correct orientation with the help of Bluejets.

    However just to clarify, the marking of pin "one" on the component does me no good if the board it is going on gives no indication of where pin 1 should land. Nor do any true schematics or diagrams exist for this particular amplifier. There are only derivative schematics for another similar model known to exist. Without any of that the only way to know which way the pins should face is to know how the currents/signals etc are flowing through the component. If you know the basics of how a BJT works, then it is easy to determine whether the pins go one way or flipped 180 degrees right? I started the thread because I was not totally familiar with the way FETs operate and wanted to validate my gut feelings about how it should be oriented. This 6 pin dip is somewhat electrically symmetrical and there is no VCC or ground pin that would make orientation immediately known.

    Tell me how you would have known which way to insert it, without prior knowledge, silkscreen markings or a diagram?
     
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