JFET reversibility question

Discussion in 'The Projects Forum' started by Darkstar, Sep 18, 2010.

  1. Darkstar

    Thread Starter Member

    Sep 3, 2010
    104
    0
    Hello,

    I have a p-channel JFET, NTE 326, and I'm wondering if the source and drain are reversible on this particular FET? I've seen datasheets for
    this and NTE gives the pinout ID, but they don't say if it is reversible nor do they give a symbol indicating this. Does anybody know?
    If not reversible, what are the chances I've damaged the FETs?
    PS. I'm operating in the ohmic region.

    Thanks
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Can you please elaborate on what you mean by reversable?

    hgmjr
     
  3. Darkstar

    Thread Starter Member

    Sep 3, 2010
    104
    0
    Hi Hgmjr,

    Some JFETs, such as the MPF102, are made so that the source and drain are interchangable. It does not matter how it is wired into a circuit, it will work the same either way. Other FETs cannot be wired with the source and drain reversed. I think I have wired my p-channel NTE326 with the source negative and the drain positive, which is wrong. NTE datasheets do not say if this FET's source and drain can be reversed or not. If not, I'll have to rewire the FET to correct the connections and hope I haven't damaged the FET when I tested the circuit.

    Thanks
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    I have never heard of any FETs being reversible.

    How much current did you push "backwards" into the FET?
     
  5. Darkstar

    Thread Starter Member

    Sep 3, 2010
    104
    0
    Hello Retched,

    Some people say most if not all FETs are reversible, but I've read that some are and some are not. They have different circuit symbols too.
    See pic.

    The NTE 326 can take 9 mA. I went up to 8 mA with only about 1 volt Vds, or thereabouts. It was only for a few minutes.

    Thanks
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Most if not all Jfets are made symmetrically so that their drain and source can be swapped and they work exactly the same.
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Huh! good to know.

    All these years and I never knew that.
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I too believe that JFET devices as a general rule can have their source and drain reversed as long as you take that into consideration when biasing the gate.

    hgmjr
     
  9. Darkstar

    Thread Starter Member

    Sep 3, 2010
    104
    0
    Thanks hgmgr
    Thanks audioguru
    Thanks audioguru
     
Loading...