Conventional vs. Electron flow notation

Discussion in 'General Electronics Chat' started by Quasimojo, Jul 3, 2010.

  1. Quasimojo

    Thread Starter New Member

    Jul 1, 2010
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    For the purposes of circuit notation, is the matter of conventional or electron flow direction simply established by the polarity noted on the power source relative to directional components such as diodes? In other words, if I see the (+) side of the power source connected directly to the forward side of the diode (allowing current through), then I am looking at conventional flow notation, whereas reversing the polarity of the notation for the power source (leaving the rest of the symbols the same) would change the entire circuit notation to electron flow notation?

    Therefore, can I simply look for the first (by first, I mean closest to the power source) directional component to determine the notation used in the schematic?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's not as simple or as complicated as that. A bit more familiarity with terminal naming makes it more clear, for one thing. Diodes have an anode and a cathode. They are forward biased when an applied voltage makes the anode positive relative to the cathode. Simply applying a positive voltage to the anode (your forward side?) does not mean a forward bias, though. The voltage on the cathode must also be known.

    There are two problems with this statement. The first is in the meaning of "conventional" flow, especially as applied to electrons. The originator of conventional flow is Ben Franklin, who imagined that electricity entailed a movement of positive charges.

    Ever since a long series of experiments back in 1907, the electron has been proven to be the charge carrier, and that it carries a negative charge. Conventional flow, then, is incorrect, as there are no positive charge carriers in wires. The orientation of a diode in a circuit can't alter this.

    Referring to "the" diode is a bit confusing. Any diode in a circuit may be there for some purpose that does not involve simple conduction when the power is turned on.

    If you have some circuit in mind, then posting it may help us all to get on the same page, so to speak.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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  4. Quasimojo

    Thread Starter New Member

    Jul 1, 2010
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    Thanks for the attempts at helping me understand this. To clarify, consider the following circuit from the eBook (for the purposes of this question, please disregard the notes on whether or not the current is permitted and assume that both schematics are designed to facilitate current):

    [​IMG]

    With the assumption being that the circuit is designed to be operational, I can deduce that, in the first circuit, since current can only pass through the diode in the clockwise direction, and that since that the power is supplied by the positive pole of the power supply, that the diagram uses conventional flow notation. Whereas, in the second diagram (also assuming that the bulb lights), since the flow begins at the negative pole and proceeds through the diode, it uses electron flow notation.

    I guess what I'm asking is quite simply, is this a reliable method of determining which notation is being used in a schematic, so that I can accurately ascertain the properties of the various parts of the circuit?

    Thanks.
     
  5. debjit625

    Well-Known Member

    Apr 17, 2010
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    No you have to understand a bit more its simple.
    Conventional flow states that current flows from positive to negative.But in real nothing flows from positive to negative, its electrons which flows in a circuit and it flows from negative to positive.Now for diodes it have two layers one P type (Positive) named anode and another side N type (Negative) named cathode ,so to forward bias the diode you have to connect the positive side to P type (Anode) and negative side to N type (Cathode),as for schematic symbol of the diode it use conventional direction of current so the anode of the diode is kind of arrow pointing towards the negative side.

    No ,for the example of the diode you will give a reversed bias to the diode.Its not about polarity marking its how the current is flowing.

    In most textbook for schematic symbol we find conventional circuit notation and also in most softwares, but in real its something else.I use the direction of electrons every time but in case of schematic i have no other option.

    Good Luck


     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Actually the circuit and the chosen convention for current flow are totally independant.

    This means that you can take any circuit and so long as you apply one convention consistently you will get the same right answer.

    Alternatively you can say that whichever convention you choose will lead to the same circuit to create the same functionality.

    As a tip, the arrows in diodes, transistors etc point in the direction of conventional current.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is a mechanism in a battery to move positive charge. In the external circuit, charge is always and only due to electron motion. Since those charges are all negative, that is all there is to it.

    Schematics do not obey a differing charge flow notation. A schematic is a map of the elements in a circuit that details their interconnections. Electrons are the charge carriers.

    To use the illustrations as an example, the one on the left shows a forward biased diode, permitting current to flow and light the lamp. On the right, the diode is reverse biased, and does not allow current flow.

    Note: I see studiot got in ahead of me. He is quite correct - the circuit works for either convention. We (ha!) try to keep to the electron flow model to (ha!, again) try to eliminate confusion. It's easier to use one convention, especially if you're just learning this stuff (or so we think).
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I'm on steroids tonight.
     
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