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Unijunction transistors still being used?

Discussion in 'Electronic Design' started by Chaos Master, Oct 24, 2003.

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  1. Chaos Master

    Chaos Master Guest

    Is there any modern application which uses the now-forgotten UJT transistors?
    And what about a manufacturer that still makes it (except NTE, obviously, which
    probably makes them for replacements)?
     
  2. I have no idea if anyone makes them. But in a number of uses for the 555
    timer, one could just as easily use a unijunction.

    Michael
     
  3. Paul Burke

    Paul Burke Guest


    Don't know about UJTs, but what about GTO thyristors? Have they died
    too? Bubble memory never really made it, though.

    Paul Burke
     
  4. Tim Jackson

    Tim Jackson Guest

    Who's forgotten?

    They are still around, eg 2N2646, the ones I have seen lately have
    "Motorola" on the data sheet.

    They were commonly used to generate trigger pulses in low-cost thyristor
    drives for DC motors, and I think drives that use this technique are still
    in manufacture. It is a cheap and simple way of hard-firing a thyristor to
    deal with highly inductive loads.

    There was also a related device, an SCR with all four layers connected to
    pins. Depending which gate pin you used it functioned either as a thyristor
    or as a "programmable unijunction". I saw these used very effectively as a
    ring counter and digit driver in Nixie tube displays (one device functioning
    both as bistable latch and high voltage driver) but I haven't seen any for a
    while now.


    Tim Jackson
     
  5. Tim Jackson

    Tim Jackson Guest

    Haven't seen GTOs for ages. Never saw the point of them myself. It took so
    much gate current to turn them off. It was just as easy to turn off
    thyristors (eg in light sensitive flash guns) by tying two thyristor anodes
    together with a capacitor, and then you were using all industry-standard
    parts and it cost no more than the gate driver.

    Tim Jackson
     
  6. Yes, they're still made, at least PUTs are. I don't think true UJTs
    are. They are probably still used in the same applications they were
    20+ years ago. Onsemi, for example. They're cheap- around a dime in
    quantity- we paid about double that way back when.

    Best regards,
    Spehro Pefhany
     
  7. Chaos Master wrote...
    I'm sure UJT and PUJTs are still very useful for micropower oscillators, as
    we described in AoE page 968, and in various SCR and Triac timing circuits.
    The old Motorola 2n4870 / 2n4871 UJT data sheet says "not recommended for
    new designs," but both parts are still in stock at distributors like Newark.

    The more popular 2n6027 and 2n6028 PUJTs are in full production by ON Semi
    and are widely available with large quantities in stock at low prices, e.g.
    9.6 cents for the 2n6027 qty 2.5k at Newark and Future, a bit more for the
    more sensitive 2n6028 part. You can buy a new 2n6028 for 16.8 cents from
    Newark, or you can pay 89 cents for one of the NTE warehoused parts. :>)


    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  8. Phil Hobbs

    Phil Hobbs Guest

    The other thing I've used PUTs for is diode laser interlocks. The
    2N6027's properties are a nice match for this application--rather like a
    latching relay, but much faster acting, work in a low current range
    without dry-contact worries, very simple to design with, and extremely
    cheap. Of course it's true that you can do the same with a couple of
    transistors and a resistor or two, but having all that in one package
    makes it less likely to be put together wrongly, which could lead to an
    unsafe condition.

    One could use a 555-type circuit as well, but in safety applications, I
    worry a lot about how the circuit behaves during power supply faults,
    e.g. sustained undervoltage, where SPICE models are even more unreliable
    than usual and variation between manufacturers is liable to show up.

    Cheers,

    Phil Hobbs
     
  9. John Larkin

    John Larkin Guest


    Ah, memories. A PUT, three resistors, one cap, and a TTL flipflop made
    a pretty good one-shot, back before there were decent TTL one-shots.
    The old Moto DTL one-shot (951?) was such a POS that nobody wanted to
    use it. I did a lot of haywire async logic - rc delays, oneshots,
    stuff like that - before an ex-TI guy took pity and explained
    synchronous machine design to me.

    John
     
  10. Luhan Monat

    Luhan Monat Guest

    UJT's ?? PUT's??

    I want to know what ever happened to Devo!
     
  11. cpemma

    cpemma Guest

    The 2N2646 is still readily available (I've one with "HEU" on the can), but
    is expensive in 1-offs (I can get four 555s for the price) and the very
    broad spec range for intrinsic stand-off ratio doesn't recommend it for some
    applications. I got mine for a simple PWM circuit, then worked out I could
    get a more forecastable sawtooth with an op-amp and use another as a
    comparator, killing two birds with one LM358.
     
  12. NTE doesn't make anything. They buy a hundred thou of the cheapest
    transistor and buff/grind off the logo and label, and relabel them to
    their NTE number.

    UJTs have never been common, just not used as much since the 555 has
    been out.

    --
    ----------------(from OED Mini-Dictionary)-----------------
    PUNCTUATION - Apostrophe
    Incorrect uses: (i) the apostrophe must not be used with a plural
    where there is no possessive sense, as in ~tea's are served here~;
    (ii) there is no such word as ~her's, our's, their's, your's~.

    Confusions: it's = it is or it has (not 'belonging to it'); correct
    uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
    but ~the dog wagged its tail~ (no apostrophe).
    ----------------(For the Apostrophe challenged)----------------
    From a fully deputized officer of the Apostrophe Police!

    <<Spammers use Weapons of Mass Distraction!>>

    I bought some batteries, but they weren't included,
    so I had to buy them again.
    -- Steven Wright

    FOR SALE: Nice parachute: never opened - used once.

    (Problem) Evidence of leak on right main landing gear
    (Solution) Evidence removed

    F
    o
    d
    d
    e
    r

    f
    o
    r

    s
    t
    u
    p
    i
    d
    "
    n
    o
    t

    e
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    e
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    m
    s
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    ..
     
  13. And vice versa. But the RCA hobby electronics manual substitutes two
    transistors, an NPN and a PNP, connected as a PUJT or whatever (pseudo
    4-layer device), for several of their circuits. For examples, see
    http://www.4qdtec.com/putpr.html



    --
    ----------------(from OED Mini-Dictionary)-----------------
    PUNCTUATION - Apostrophe
    Incorrect uses: (i) the apostrophe must not be used with a plural
    where there is no possessive sense, as in ~tea's are served here~;
    (ii) there is no such word as ~her's, our's, their's, your's~.

    Confusions: it's = it is or it has (not 'belonging to it'); correct
    uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
    but ~the dog wagged its tail~ (no apostrophe).
    ----------------(For the Apostrophe challenged)----------------
    From a fully deputized officer of the Apostrophe Police!

    <<Spammers use Weapons of Mass Distraction!>>

    I bought some batteries, but they weren't included,
    so I had to buy them again.
    -- Steven Wright

    FOR SALE: Nice parachute: never opened - used once.

    (Problem) Evidence of leak on right main landing gear
    (Solution) Evidence removed

    F
    o
    d
    d
    e
    r

    f
    o
    r

    s
    t
    u
    p
    i
    d
    "
    n
    o
    t

    e
    n
    o
    u
    g
    h

    i
    n
    c
    l
    d
    u
    d
    e
    d

    t
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    x
    t
    "
    e
    r
    r
    o
    r

    m
    s
    g
    ..
     
  14. Capoot

    Capoot Guest

    transistors?

    Here is a super-regenerative receiver that uses a UJT as a quench
    oscillator.
    http://www.users.bigpond.com/cool386/srrx.html
    Sorry if this post should turn out to be a duplicate.
    Ray
     
  15. Thanks for posting that link...

    I *knew* that you could do SCRs, etc. with a pair of bipolar transistors,
    but for some reason couldn't remember exactly how. Lots of other nifty
    stuff there, as well. Sometimes it's a good thing to review bunches of
    the old tricks that you've forgotten... :)

    Don't have any UJTs or SCRs around, but I sure do have a ton of generic
    bipolar devices that I've scavenged out of this and that.
     
  16. Jeff

    Jeff Guest

    A what?
     
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