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What's this component?

Discussion in 'Electronic Design' started by Wipf, Oct 3, 2012.

  1. Wipf

    Wipf Guest

    Hi,
    I'm a lurker here and I thought I'd ask for some help. I have a few
    boards I saved from the trash that appear to be little HV supplies for a
    mass spectrometer. I was trying to trace through the circuit and could
    not figure out what these components were on the (presumably) multiplier
    part of the circuit. A picture is here
    http://www.flickr.com/photos/dwipf/8051484989/in/photostream
    They look like diodes but don't read as diodes on my multimeter (maybe
    because they are in circuit). They are marked as 00B or OOB which
    doesn't seem to be any diode code that I can find.

    Any thoughts?

    Thanks
    David
     
  2. Wipf

    Wipf Guest

    Thanks, I think it is a multiplier but my question is specifically about
    the "diodes" marked 00B. I couldn't find any info on their specs and, in
    fact, don't read as diodes using my DMM.

    David
     
  3. tm

    tm Guest

    They are high voltage diodes and have a large forward voltage drop. Maybe up
    to 10 volts or so. They are made up of many series diode junctions in order
    to get the high reverse voltage needed.

    Try forward biasing to diode through a current limiting resistor with maybe
    24 volts and 10 k ohms. Measure the forward voltage drop across the diode.
    You can do this in circuit.

    Tm
     
  4. gregz

    gregz Guest

    Try something RX 1K or higher to get more voltage. Depends on the meter,
    some have nine volt batteries on high ohms.

    Greg
     
  5. if you have a simpson 260, there is enough voltage to get the meter to
    move a bit ;)

    Cheers
     
  6. tm

    tm Guest

    Those little diodes don't have very many junctions so you would be right.
    Some of the >10 kV diodes drop 10 -15 volts (or more) forward. I still use
    my 260 but you need to be careful. It can do a pretty high current for some
    solid state devices now days.
     
  7. Lord Valve

    Lord Valve Guest

    Multiple-pellet stabistors.

    Lord Valve
     
  8. That is called a "nomenclature".



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  9. Wipf

    Wipf Guest

    I can do that. It sounds like that's the consensus on them. I wasn't
    aware that HV diodes had such a large Vf.
    Thanks
    David
     
  10. Wipf

    Wipf Guest

    I have posted curves here, the Vf is about 12 V at 20 mA but the curve
    is non exponential.
    http://www.flickr.com/photos/dwipf/8054927724/in/photostream (log)
    http://www.flickr.com/photos/dwipf/8054927808/in/photostream
    http://www.flickr.com/photos/dwipf/8054927621/in/photostream (linear)

    For comparison, also the 1N4005 diode and a BYV-27-200 Avalance diode
    also on the board.
     
  11. gregz

    gregz Guest

    I blew out a large photodiode with a triplet. I was able to see the contact
    wire blown like a fuse.

    Greg
     
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