Surge suppression using a Zener diode or tvs question.

Discussion in 'Power Electronics' started by fluxanode, Sep 9, 2019.

  1. fluxanode

    Thread Starter New Member

    Mar 23, 2014
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    Surge suppression using a Zener diode or tvs question.

    If the zener or tvs is not conducting in a over voltage situation, won't noise on/from the ground be fed back from ground to the protected circuit? Is there a method to stop ground induced noise and voltages?
     
  2. dl324

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    Mar 30, 2015
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    Welcome to AAC!
    Where would the zener or TVS pick up noise?
     
  3. Hymie

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    Mar 30, 2018
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    Why would a zener or TVS not conduct in an overvoltage situation?
     
  4. fluxanode

    Thread Starter New Member

    Mar 23, 2014
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    Sorry i meant undervoltage like when using the zenor to catch a voltage surge by being connected to the positive rail and ground and under normal conditions it is not conducting in reverse until the threshold is reached. If i understand correctly the zener only conducts in reverse when an over voltage range is exceeded. So consider when it is not conducting because the voltage line it is protecting is under the "zener" break over range. Won't it allow transients and noise from the ground into the rail? Because the diode doesn't block anything from the ground inbound to the rail?
     
  5. dl324

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    You're getting way into the weeds.

    If the zener isn't conducting, it can't conduct transients between the power rails. If transients exist in the circuit you should use one or more of the usual methods to suppress them.
     
  6. fluxanode

    Thread Starter New Member

    Mar 23, 2014
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    What? Doesn't a diode conduct from the anode to the cathode? But with a zener when the zener is reversed biased over the zener voltage then it conducts cathode to anode right? I believe this is what makes it a zener which can act as a TVS or regulator. Am I wrong in this assumption? So to simplify my question, is or can noise on the anode side (ground) be induced across the diode from anode to cathode? Look into the application of a Zener barrier http://www.sensorland.com/HowPage120.html. I have been told that the application of the zener barrier can cause addition of noise. So is there a suggestion of how to reduce the noise? Maybe another diode to block ground noise from a ground that is noisy?
     
  7. dl324

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    When you're using a zener or TVS as over voltage protection, they don't conduct unless there's an over voltage condition.

    If you're using a zener as a voltage regulator, any so called noise from the diode can be filtered. Noise exists in all circuits. You don't need to worry about it unless the magnitude is large enough to cause incorrect operation.
     
  8. fluxanode

    Thread Starter New Member

    Mar 23, 2014
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    If you know anything about instrumentation on a offshore platform or any drilling rig for that matter, then you would understand my application and yes the noise and sometimes voltages on the ground can be quite large at times. Now this is mostly unusual but it happens and my equipment has to be made to tolerate the unusual as well as the nominal. In this case the Zener is not used as a regulator but as a "safety relief valve" to limit a sparking voltage from the source to get out of my equipment. The zener conducts the high voltage spike and current to ground and causes a fuse rated below the spark value (as outlined in the NFPA reg's) in its circuit to blow, thus preventing a spark from happening in an environment where you don't want a spark like an explosive gas atmosphere. I don't think you understand this type of requirement, maybe someone else on here has a suggestion or comment.
     
    Last edited: Sep 9, 2019
  9. dl324

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    Ok. You're now on my ignore list.
     
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  10. shortbus

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    Don't you think you should have put that, what you're working with, in the first post?

    If you understand it, why are you asking questions about it from unknown people in a forum?
     
  11. fluxanode

    Thread Starter New Member

    Mar 23, 2014
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    Short bus, your are correct and my tone was not too nice, so I apologize to dl324 and anyone else...

    I understand my application yes, but I have been informed by other engineers that the zener is only "ok" but it allows ac noise into the line. But they can't tell me any method to block it out. Cap and inductors as filters are not allowed because they allow storage of energy and may cause a condition where the circuit has enough potential to make sparks. I came here because after following the posts it is obvious that there are some smart people on this forum and maybe I can get some answers to my question and suggestions I can try.

    Thanks
     
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  12. RPLaJeunesse

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    Jul 29, 2018
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    I think there is some confusion of what "zener" means in a system versus a circuit. A) The zener barrier in the article you reference is a system component - not simply a "zener diode" - and is shown applied with multiple grounding points. It's that multiple grounding points that can allow induced noise current on the load's ground lead. Since all wires have some resistance a noise voltage is induced between points on the wire. That may or may not be significant here. B) Usually folks think of a zener diode as a circuit component, applied in a circuit to clamp the voltage between two nodes to a fixed maximum. A unidirectional TVS diode is a glorified zener diode, a bidirectional TVS is essentially two TVS diodes back-to-back. As for the zener conducting from anode to cathode, that only happens when the anode is at a somewhat higher voltage than the cathode, i.e. the supply lines are hooked up backwards! Hopefully that won't happen. Also remember that circuit voltages, especially noise voltages, are always measured between two points. So there is no such thing as "noise on (whatever)", since there is no indicated second point of measurement. (There can be current noise in a line, but that's what ferrite beads and filter inductors are for.)
     
  13. SamR

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    Mar 19, 2019
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    Are you are having noise issues using an intrinsically safe barrier system in a hazardous classified environment? Is that the issue? When you said zener I and others here immediately thought the zener diode component.
     
  14. SamR

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    Mar 19, 2019
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    Not in my ~30 years working with instrumentation in explosive environments. The grounds need to be tested, shielded twisted pair cables shielding grounded. No experience on oil platforms but dealt with hydrogen gas and flammable volatile liquids. Noise would only be introduced by poor grounding, ungrounded shielding, loose connections or non-twisted pair cable capacitance. I would think that would be especially true insuring proper ground in a marine environment with higher-powered VHF and HF radios in use. Not familiar with that particular brand and our barriers were not fused.
     
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