name that diode

Discussion in 'General Electronics Chat' started by jut, Jan 23, 2011.

  1. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    [​IMG]
     
    Last edited: Jan 23, 2011
  2. Wendy

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    Mar 24, 2008
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    I've played this game! Your picture is better though.

    First guess, it is a small signal diode, similar to a 1N914.

    You could connect it to a 20V power supply and reverse bias it to see if it is a zener.

    The LED museum had a similar looking device that was an early LED.

    Without markings it is almost impossible to be sure.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh, if you connect it to a 20v power supply, the supply better be current limited or you'll have a glass passivated open connection with some burned rubble in the middle. :eek:
     
  4. Wendy

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    Mar 24, 2008
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    Opps, did I forget that little detail. It was in my head. :D Figure a 100KΩ resistor in series with it.
     
  5. Ron H

    AAC Fanatic!

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    It looks like a point contact diode to me. I'm guessing it's germanium, maybe 1N34A.
    If you look closely at the OP's picture, the s-curve in the catwhisker appears to be there, seen "on edge".
     
  6. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    It's not a zener. I do believe it's a schottky because there is no reverse recovery time as measured from my scope. This diode looks like an old "cat whisker" from way back in the day. I was curious to see if anyone recognized it.
     
  7. Ron H

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    Did you see my post? Google "point contact diode" (images).

    This site has great pictures of diode internals.
     
  8. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    The whisker has a bend, not so much an "s".
    [​IMG]

    mmm, is that gold?
    [​IMG]
     
  9. Ron H

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    Looks a lot like this one, from the site I referenced in my previous post.

    It is curious that you could see no reverse recovery time, because I don't think it looks like a Schottky diode.
    How are you measuring Trr?
    EDIT: I can't find a Trr spec on any germanium diode.
     
    Last edited: Jan 24, 2011
  10. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    [​IMG]


    With a PN diode (FR3T):
    [​IMG]


    With the mystery cat whisker diode:
    [​IMG]
     
  11. Ron H

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    I'm not sure how to interpret your time scale.:confused:
     
  12. jut

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    Aug 25, 2007
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    That's 500ns per div.
     
  13. Ron H

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    I'm trying to simulate this. What is the capacitance of your probe?
    The diode in the top picture must be a pretty big one. What type is it?

    EDIT: What are the rise/fall times of your generator?
     
  14. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    I couldn't find the capacitance of these Rigol RP2200 1x/20x probes. The front panel of the scope says "all inputs are 1Mohm//15pF" though.

    Rise/fall time is about 20ns.

    Diode in top picture is a Toshiba FR3T. See attached datasheet.
     
  15. Ron H

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    With 20nS transition times, you won't see the Trr of a small-signal diode. For example, 1N4148 has a Trr of 4nS. I suspect point contact diodes are in that same range, because their junctions are tiny. From Wikipedia:
     
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  16. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    Interesting, thanks.

    So my BK 4011 function generator has 20ns rise/fall times. A higher end model like the hp33120a has the same rise/fall times. I wonder what instrument can give me faster rise/fall times to test this sort of thing (trr of diodes)?

    ps - found a picture of my diode here:
    http://www.crystalradio.net/detectors/
     
  17. Ron H

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    I could probably design a little circuit for you that would allow you to do this. You could still drive it from your function generator.
    If you want me to do that:
    What power supplies do you have available?
    Do you have a stock of transistors and resistors? If not, who would you order from?
     
  18. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    I have a ±(12 to 15)V @1A supply. I have a 0-20V @ 200mA supply. The latter is kinda flaky, it's an old RCA.

    I have an extensive array of resistors: 1% and 5% kits. I have some typical transistors: 2n2222a (npn), 2n3906 (pnp), 2n7000 (n fet).
     
  19. Ron H

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    I'll try to use trannies that you have. If that doesn't work, you might need to buy a few.
     
  20. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    I've got some other transistors; I just don't have a good idea of my inventory, as i'm away from my home lab. I'll write back later with more info.

    Thanks for the help :D
     
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