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Spikes on Zener Clamp Circuit

Discussion in 'Electronic Design' started by rich, Dec 19, 2007.

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  1. rich

    rich Guest

    I am using a zener clamp to regulate a messy signal down to a level
    that will cause an interrupt in a microcontroller. The circuit works
    fine but I am seeing some troubling spikes on the output, both
    negative and positive.
    The input signal is a reoccurring ~150Vpp ringing signal.

    I would appreciate any ideas....

    See details at:

    http://members.dsl-only.net/~rsoennichsen/zener_clamp.htm

    Rich
     
  2. Andrew Holme

    Andrew Holme Guest

    Those spikes look uncorrelated with your CH2 input signal. Do you still get
    them even if you touch the CH1 'scope probe to ground at the diode anodes?
    In electrically noisy environments, you can pickup huge impulses on a
    single-turn loop formed by connecting the probe ground lead to the tip.

    You could add a little filtering to your input circuit using series
    inductance (e.g. ferrite beads) and/or shunt capacitance.
     
  3. whit3rd

    whit3rd Guest

    High slew rate signals might result from inductive coupling of wiring
    near the clamp. The Zener clamps the conducted signal, but the
    wire in series with that signal can couple, as a transformer winding,
    to the input.
     
  4. BobW

    BobW Guest

    What is it you've captured? That signal has a period of 100us (10kHz), but a
    standard ringing signal is usually 20Hz.

    Bob
     
  5. rich

    rich Guest

    I think you may be on to something. I will ground the scope probe
    right next to the tip and see what it looks like. The ferrites are a
    good idea too.

    thanks

    rich
     
  6. Why use a diode? A zener is a diode the other way around.
     
  7. Fred Bloggs

    Fred Bloggs Guest

    LOL- subtle...
     
  8. Fred Bloggs

    Fred Bloggs Guest

    Is it really necessary to dissipate a full Watt to drive a micropower input?
    This circuit has a fairly huge working input range of amplitudes it will
    handle at your frequency:
    View in a fixed-width font such as Courier.
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Scratch the above. It should be:
    View in a fixed-width font such as Courier.
     
  10. Jamie

    Jamie Guest

    Hmm, I guess my first question would be:
    1.
    Are you using a 10:1 probe to measure that?

    2. Do you have near by R.F. and maybe the diodes or
    uC input is rectifying depending on what side you check?

    3. Did you account for parasitic conditions with the construction
    of the traces, components etc... ?

    ----------------
    P.S.
    Zeners are know to be slightly slow. Don't know if this is an
    issue on your end but it might be worth looking into?


    --
    "I'd rather have a bottle in front of me than a frontal lobotomy"

    "Daily Thought:

    SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
    THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
    http://webpages.charter.net/jamie_5"
     
  11. How about an analog scope - could the digital sampling be playing tricks?

    joe
     
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