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A Tunnel Diode Paradox

Discussion in 'Electronic Basics' started by [email protected], Sep 29, 2008.

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  1. Guest

    Suppose that a tunnel diode wired in series with a load resistor is
    connected to a battery. The load resistor value is chosen so that the
    resistor load line passing through the negative resitance region of
    the tunnel diode will intersect the tunnel diode curve in three
    places.

    Which of the three current values will the tunnel diode choose and
    why?

    I am having a little trouble finding a "cheap" source for tunnel
    diodes or tunnel diodes in general. I found a couple of sources on
    the web wanting $27.00 a piece for a 1N2934A . I was expecting maybe
    something in the range of $0.75 - $1.50 .


    Any help would be greatly appreciated. Thanks
     
  2. Check the date on the article or book you've been reading.

    Tunnel diodes had a very short life. They appeared really useful,
    but generally weren't. They were a neat curiosity, and thus made
    waves in the hobby magazines and hobby books, but there was nothing
    that other devices couldn't do. They were in those hobby publications
    because "hey neat, a diode can oscillate and amplify, and sometimes
    both at the same time".

    Commercially, the only really long standing use seems to be triggers
    in oscilliscopes. That's the only real use anyone has posted about
    in these newsgroups in over a decade.

    Hobbyists ask about them, not realizing they are long out of
    circulation.

    They are expensive because they were made for a short period of time,
    and that was forty years ago. The real prime was the early sixties.
    If they are in production today, it is a very small production.

    There is no reason (other than for those oscilliscopes) to use
    a tunnel diode today. Anything you can think of can be done
    other ways, and with cheaper and more commonly available parts.

    If you really want to play with one for the sake of it being
    a tunnel diode, then you have to pay the price.

    Michael
     
  3. I know one VARIAN Raman-Spektrometer with a TD in it's cicuit.
    Probably in some sort of discriminator/trigger.
    That was about 1975...

    Yours, Holger
     
  4. Andrew Holme

    Andrew Holme Guest

    It won't stay in the negative resistance region if the load line
    intersects at 3 points; it'll choose one of the two stable states.
    You can force it to assume the lower voltage state by temporarily
    making the diode current less than the valley current. You can force
    it to assume the higher voltage state by temporarily making the diode
    current exceed the peak current.
    I bought a couple on e-Bay. They're rare and expensive.
     
  5. Wim Lewis

    Wim Lewis Guest

    FYI, if all you want is to experiment with negative-resistance circuits,
    you can get a vaguely tunnel-diode-like I-V characteristic by connecting
    a pair of transistors:

    http://www.zen22142.zen.co.uk/Theory/neg_resistance/negres.htm
    http://users.tpg.com.au/users/ldbutler/NegResDipMeter.htm

    And I hadn't run across this before today, but apparently you can get a
    negative resistance out of a common PN2222A, too:

    http://jlnlabs.online.fr/cnr/negosc.htm
     
  6. neon

    neon

    1,325
    0
    Oct 21, 2006
    Tunnel diodes are stil are there? first of all you cannot put a battery and expect the tunnel to stand still. Guaraty oscillation. actualy if you want a very fast oscillator that is the device to use. Problems are there the valley current is not stable and god knows the temperature stability is nowhere to be found. I used them a very long time ago for hi speed switches before comparators came out. but you try but in the end you will found out that they are worthless.
     
  7. terryS

    terryS Guest

    And there is an article somewhere entitled, IIRC, "A crystal that can
    oscillate". Or something like that. Written in the in the 1920s in
    reference to 'crystal set detectors' it talks about what for all the
    world sounds like a negative resistance diode. Note.

    A later comment was that this might have been a narrowly missed chance
    to have discovered the solid state transistor! But tubes were just
    being perfected and it was not til WWII was over effort was put
    towards solid state devices!

    Recall that when first found the article I figured it was just
    something about biasing the crystal detector with an adjustable (bias)
    battery voltage so as to place it in the most efficient region for
    detecting the modulation content of radio signals! But it was more
    than that.

    Will see if I kept record of it somewhere?

    Ah. Maybe this was it (The crystodyne!) http://earlyradiohistory.us/1924sens.htm

    Also this link: http://home.earthlink.net/~lenyr/znrfamp2.htm
    ,is interesting.
     
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