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grounding in electronic circuits

Discussion in 'General Electronics Discussion' started by Masoud Torabi, Apr 17, 2015.

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  1. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    Hi dears.
    I have questions about grounding in electronic circuits. plz help me know that:
    1- does electronic circuits that working with signals need to grounding?if yes. may you make me some examples?
    2- which parts of every electronic system(power supply, ac driver, etc) must be connect to ground and how?

    my purpose in this forum is obtaining knowledge for better design. I faced with some problem that I will bring it up in other post.

    Thanks a lot.
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    hi there
    welcome :)

    Define YOUR definition of ground

    Dave
     
  3. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    yeah. i speak about ground that we connect it too body and earth wire.
     
  4. Gryd3

    Gryd3

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    Jun 25, 2014
    I think it would be best to understand what 'ground' is commonly used for. Then you can decide how it can be used.

    In 2-wire systems like automotive, the negative battery terminal is often 'ground' or 'common'. The majority of 'logic' and controls end up switching the positive voltage. The result is that you typically only need to run a single wire for 'power' and the chassis of the vehicle will be the return path.

    In signalling, the 'common' or 'ground' exists as a reference point to compare a signal too to determine if it's a high or low voltage. You cannot measure a voltage (or signal) without a reference of some kind. A bad connection to 'common' here could easily cause the signal to be degraded or misinterpreted.

    In home appliances and other larger equipment, 'Earth' ground is often used as a safety mechanism which is tied to the case of the device. The idea is that the electricity comes into the home on the Hot Wire, and 'should' leave on the Neutral Wire... but should a wiring fault occur, the 'Earth' ground will be a suitable emergency exit path for the electricity to flow from the Hot wire to protect someone from electric shock.

    *Note that in only one instance, I used 'Earth' ground.
    Cars, mobile phones, 2-prong appliance, and other battery operated devices to not have an 'Earth Ground'. The only reason an Earth Ground works as a safety mechanism is because the Utility Company is also connected to Earth Ground! (So the Earth Ground can actually be a return path for electricity) If the Earth Ground is not actually connected on BOTH ends it will do nothing for protection.
     
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  5. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    thank you. it was usable.
    according to your note generally ground(earth) use for safety purpose then for circuit that use low voltage signal we don't need it.
    am I true, we just connect earth to case?
    are there other connection with circuits?
     
  6. duke37

    duke37

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    Jan 9, 2011
    The layout of ground wires can be complicated. A computer used to record analogue signals can have three grounds, one to connect to the case to protect the operator from shock, one to run the digital signals and one to reference the analogue signals. These are likely to be connected together at a single point so that current through one does not affect another.

    A similar effect occurs in audio amplifiers where voltage drop along a ground connection can induce hum in the audio circuits.
     
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  7. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    well. I got it but for example in power part that has high voltage(110v or 220v), earth just connect to case or it will connect to some power elements such as TRIAC, input jack, filter coil, capacitor and etc?

    an example may help me(Thanks).
     
  8. BobK

    BobK

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    The other place an actual earth ground is important is in radio transmitters and sensitive receivers. When used with a monopole antenna, the earth ground is the other terminal.

    Bob
     
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  9. garublador

    garublador

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    Oct 14, 2014
    If you have high voltages you should follow UL type safety standards for grounding. "Complicated" is a pretty nice way to put it. You'll probably find more colorful adjectives once you start reading the safety requirements.
     
  10. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    dear, how can I find this safety manual?
    what's its keyword?
     
  11. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    what's your idea about this kinds of earth structure? Untitled.jpg Untitled.jpg
     
  12. garublador

    garublador

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    Oct 14, 2014
    It depends on where you want to sell this product and what type of product it is. In the US it's "UL" that has defined the standards:

    http://ulstandards.ul.com/

    UL standard 60950-1 is one such standard I've seen that might apply. You'll have to find which organization and which standard applies to you the best. With how little information I have on what you're doing that's about as specific as I can get.
     
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  13. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    thank you all.
    I learned lots of things about grounding and earth system.
    but let me know about practical circuits like once that I sent. what's its idea? it's a common circuit that you plug power cable to jack, after that 220 volt electricity enter to and face with this circuit. after that electricity will go to pulse filter or transformer.
    why it link both line to ground via capacitors(100nf)?
     
  14. garublador

    garublador

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    Oct 14, 2014
    Those two capacitors to earth ground are there to filter out common mode noise.
     
  15. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    well. and do you remember more tips like example?
     
  16. Gryd3

    Gryd3

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    Jun 25, 2014
    How about you provide an example product and if anyone is willing, they can provide the user of 'ground' and if it's an 'Earth Ground' or simply a 'Common'

    Do you understand the difference between Earth Ground, and Common?
     
  17. Masoud Torabi

    Masoud Torabi

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    Apr 17, 2015
    yeah tnx.
    and my main problem was about earth for safety and EMI.
    Like >> Ctrl+A
     
  18. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    Ground for safety typically has the case of the object tied to Earth Ground.
    This reduces risk of shock if there was a short or open circuit within the object, where the object could potentially be connected to the Hot wire in this case. The circuit breaker would then trip do to excessive current flow. If the ground is 'not' connected and a person touches the appliance, and is also touching something that is grounded the person will then become the new exit path for the Hot wire causing electric shock.
    A real life situation is when my Aunt bought a new house. The Stove and Fridge were in close proximity to each other, and one of them was not grounded. She made the unknowing mistake of touching both appliances at the same time, and the appliance that was not grounded used her touching the grounded appliance as a ground and gave her a nasty shock. Luckily she was unharmed.
    Same situation for my parents buying a used home, the toaster oven was in close enough proximity that the lip of the sink could accidentally be touched when you lean into the corner of the counter to use the toaster. The plug did not have it's ground prong correctly attached to ground. The sink however, was connected to earth ground, as the sink, and all plumping was conductive. This only resulted in a mild tingle however, but is still dangerous.
    Needless to say, it is 'very' important to use a ground properly and consistently.

    As far as EM shielding is concerned, this does not always require a 'ground'. It could simply require that the shielding on a cable is connected to the negative terminal on the battery. This would be 'common', and would be used with the logic circuits were powered and controlled from the positive voltage rail. The purpose of the shield is not so much to eliminate EM radiation, but to divert it. If left unshielded, the EM radiation could be picked up by other components in the device instead of harmlessly being diverted away to the battery.
     
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