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National PF5301 cross reference

Discussion in 'Electronic Components' started by JW, Jun 28, 2013.

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  1. JW

    JW Guest

    Looking for a suitable cross-reference for a National PF5301 TO-92 N
    channel JFET as I can't find the original part anywhere. Hell, I can't
    even find an original datasheet. The critical parameter for the sub is
    Igss which for the National part is 1pA. The only thing I've been able to
    find so far is a Linear Systems LS5301 which has a Ig of 1pA, but at $40 a
    pop (!), I'd like to find an alternate.

    Does anyone know of any possible substitutes?

    Thanks.
     
  2. JW

    JW Guest

    I'm pretty sure I do, as it looks to be a fairly sensitive circuit. It's
    for a repair on a Keithley 220 programmable current source.
    http://www.google.com/url?sa=t&rct=...k4GgCQ&usg=AFQjCNHiyEb7xQJn29nTeEEYYk4sluspuA

    The schematic is on page 6-31/6-32 (4 pages from the end) location Q302
    near the top of the page. It's part of circuit which uses a AD515K
    FET-Input Electrometer Op-amp.

    Thanks.
     
  3. JW

    JW Guest

    ITYM PN4117A and PN4118A. [Google] Or maybe so?

    Those do look good and there seems to be some out there, but I'm not too
    crazy about sources that ask for a RFQ only to tell you that they have a
    $100 minimum. Was hoping for something I could buy at Digikey or Mouser or
    some other distributor with no minimums.

    Although there is a Vishay 2N4117A-E3
    http://www.mouser.com/ProductDetail...sGAEpiMZZMv4z0HnGdrLjmW9PdigBgHUXen39y4wHUM=I
    I wonder what the -E3 means? I found a datasheet, but it does not state
    what -E3 is.

    Vishay also has a 2N4118A.
    http://www.mouser.com/ProductDetail...=sGAEpiMZZMv4z0HnGdrLjmibscKjQIlodZHJqghFYzA=
    In stock too. Maybe I'll give that one a go, wrong package but beggars
    can't be choosers.

    A pity that these are all EOL. *sigh*

    Thanks, Jeff.
     
  4. What's the application? Do you really need a jfet?

    I'm pretty sure I do, as it looks to be a fairly sensitive circuit. It's
    for a repair on a Keithley 220 programmable current source.
    http://www.google.com/url?sa=t&rct=...k4GgCQ&usg=AFQjCNHiyEb7xQJn29nTeEEYYk4sluspuA

    The schematic is on page 6-31/6-32 (4 pages from the end) location Q302
    near the top of the page. It's part of circuit which uses a AD515K
    FET-Input Electrometer Op-amp.

    Hmmm... Would that -- or a similar -- op-amp be suitable?
     
  5. Hi,

    I could send you photos (don't have access to a scanner till Monday):
    interested? If yes, just contact me per PM.

    CU

    Reinhard
     
  6. o pere o

    o pere o Guest

    Did you get the fA figure by measurements? The Onsemi and the Fairchild
    give 10 nA as the leakage value. Guess they are much better than
    specified...

    Pere
     
  7. Joerg

    Joerg Guest


    How about this?

    http://www.trendsetter.com/v/vspfil...grated Systems/SST440, SST441, U440, U441.pdf

    Around $8 but there's two in the package.
     
  8. I expect they can't be bothered to test them; it would take too long to
    resolve fA I think. But 10nA is huge.

    [...]
     
  9. Jasen Betts

    Jasen Betts Guest

    Hmm, JFET, so depletion; it was probably like this.

    |
    |
    |--'
    |
    .--->|--.
    | |
    | |
    | |--'
    | |
    ----|--->|--.
    | |
    `-------+
    |
    |

    JFET cascode
     
  10. Jasen Betts

    Jasen Betts Guest

    Gah! I forgot how to draw fets :(
     
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