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Positive Ground

Discussion in 'Beginner Electronics' started by Ernie Werbel, Jun 19, 2006.

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  1. Ernie Werbel

    Ernie Werbel Guest

    Hi all. I am a part-time college student majoring in Electrical Engineering
    Technology. I have been trying to learn as much as I can on my own since I
    was twelve; about ten years now. The earliest material I found was in books
    and experience in taking things apart. I learned that electrons flowed out
    of the negative terminal of the battery, through the circuit components, and
    back into the positive terminal. Hence, I have always designed my projects
    around a positive ground point. No problems there.
    Well for the past year I have finally gotten into the hardcore
    electronics-related classes at the college. Some material is familiar, but
    most of it is new. I am doing well however I have difficulty with the fact
    that the modern textbooks are showing the circuits using a negative ground.
    This seems backwards. I know the circuit will still work the same way, but
    it's hard to get myself to think in the negative-ground sense. If I look at
    a positive-grounded circuit, I can envision the electrons and make
    calculations without difficulty, but it's a different story with negative
    ground for me.
    What is anyone else's takes on this?
    Ernie
     
  2. default

    default Guest

    Can't you just assume they go from positive to negative, for the
    purpose of reading the schematics easier? Frankly I don't see what
    the difference is - I know the trons come from ground but that
    information isn't relevant to designing stuff.
     
  3. Ernie,

    You, like all EE students that have gone before you, will just have to
    accept the way +, - and the positve direction for current are defined.
    Once you recognize that it is arbitrary and doesn't really matter so
    long as you are consistent, it gets a good bit easier.

    The definition of the positive and negative in an electrical circuit was
    originally done by Ben Franklin long before the electron was discovered.
    At that time he and others understood like charged objects were
    repelled, unlike charged objects were attracted and something flowed
    when they allowed unlike charged objects to touch. They also understood
    that there was an excess of something on one of the objects that was
    equalized when you allowed objects to touch. With a 50-50 shot at
    getting it right, he just picked wrong when assigning the + and -. By
    the time that electons were discovered and found to be the primary
    current carrier in wires, it was far too late to re-define + and -.

    Now, just wait until you start learning about semiconductor theory and
    hole flow.
     
  4. Dan H

    Dan H Guest

    The assumed current flow and ground are really 2 different issues. As
    the others have stated, the direction of current flow is by standard
    convention from + to -

    Ground is a reference point for measuring other voltages and has
    nothing to do with the direction of current flow. It is the zero
    voltage point so the if a measurement is -12V it is 12 volts more
    negative than ground. If it is +5V it is 5 volts more positive than
    ground. there is no reference to current flow in these measurements

    In the early days of transistor logic NPN transistors were used and it
    was easier to design when the logic levels were 0 and -12V. With the
    advent of integrated circuits it was more convenient to make the logic
    levels 0 and +5V or now 0 and +3V

    I had an engineer that worked for me and always drew his diodes
    backwards because he had learned electron flow in the military and
    never was able to completely switch his brain to conventional current
    flow.

    Dan
     
  5. Lost'n Found

    Lost'n Found Guest

    Forget the word ground, and use the word reference- referenced to zero
    volts.
    Electrons do flow from negative to positive. Current goes from positive to
    negative. Why? Blame the man on the $100 bill!

    The way you did ur analysis before, instead of say having a battery of 12-0,
    you have battery of 0- -12v, according to the universal convention. The
    potential difference is still the same though.

    solve some ciruits, you'll get used to it.
     
  6. Daniel

    Daniel Guest

    What you mean to say is "Conventional Current flow is positive to
    negative...."
    When I did my basic electronics training, "Electron Current Flow" was
    the method used, except for about two minute mention of Conventional
    current flow!

    Electrons actually
    Big call, Geoff, to forget Electron Current flow.
    Daniel
     
  7. Don Kelly

    Don Kelly Guest

    However, except in some grade schools and a few tech institutes ,
    conventional flow is used. Definitely so at the university level in both
    engineering and physics. Actually, it really doesn't matter for solution
    purposes, which way the current flows. Sometimes you don't actually know
    until the math is worked out and if wrong the sign will indicate it.
    Consistency is the main thing and conventional current is more consistent
    overall particularly mathematically. Don't sweat it.
     
  8. Daniel

    Daniel Guest

    Why would you want me to mentally rotate all the arrows? The arrows
    always pointed to the N type material, so you knew how to set up your
    supplies!

    Perhaps the problem here is that I'm talking actual circuit operation
    where as you seem to be talking circuit analysis, Thevans, Norton, that
    type of stuff.
    Daniel
     
  9. Don Kelly

    Don Kelly Guest

    ----------------------------
    Unimportant for actual circuit operation. One doesn't count electrons or
    really care about what the charge carriers actually are except in terms of
    the internal design of transistors,etc. Otherwise you measure voltages and
    currents (and an ammeter is scaled and marked in terms of conventional
    current). However, what is the electron flow for AC?-they just wiggle
    about. Pick a convention and stick with it. Note that the conventional
    current is used by far more people than "electron flow" and is the standard
    in both physics and engineering use. You got stuck with a tech school of
    the '40's definition where all electronic devices depended on electron flow
    so somebody decided to reverse the "direction" of current (causing all kinds
    of future and unnecessary problems). --

    Don Kelly
    remove the X to answer
     
  10. Ernie Werbel

    Ernie Werbel Guest

    Ok so if I understand correctly all this it's not the way the electronic go
    that's important it's the voltage potentials? So -12V to zero is the same
    as zero to +12V?

    But then why do you need ground? It's justa voltage reference, right? Or
    does it serve some other purpose as a convenient connection point (less
    wires if they go to the chassis)?
     
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