Conventional and Actual Current on Schematics

Discussion in 'General Electronics Chat' started by fullNelson, May 11, 2012.

  1. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    3 quick questions:

    Sources on the internet say that current flows from Anode to Cathode or Positive to Negative. Is this only true when thinking about a circuit in "Conventional" electron flow?

    Is it reversed if we thinking of Actual Flow? Does current flow through from Cathode to Anode?

    The symbol for a diode shows the arrow smacking into a wall, at first I thought it made sense to see that the "arrow" of the diode was pointing in the direction of flow. However, the notion of "Actual Flow" invalidate the symbol being used.

    So if i am looking at a professionally published schematic for a product I just bought should I tihnk of the circuit in terms of Conventional flow since the diodes used in it show current flowing with the arrow?
     
  2. #12

    Expert

    Nov 30, 2010
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    You can think in conventional flow or electron flow as long as you make a conscious decision and be consistent. It's a matter of convenience.

    Conventional flow assumes that something positive flows. The truth is, electrons flow, and they carry a negative charge.

    When I look at a symbol for a diode, I see it as similar to a symbol for a speaker and the cone of the speaker emits electrons. Whatever floats your boat.
     
  3. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    I picked up Paul Falstads applet and I mocked up a simple circuit and realized he is showing as a default Conventional flow.

    I like the idea of the speaker cone. Thats what I thought of when I saw it.

    Take a look at this diagram for reference to what I am about to say below:

    [​IMG]

    So on the same topic, if I choose to think of things in terms of actual flow, then when I see a NPN transistor that is in series with a diode, then the Collector (as the Anode) is no longer receiving the electrons from the Diode's Cathode but is now Emitting them back through the Cathode on the Diode and back to the voltage source. Is that right?

    It seems like the roles of the collector and the emitter would flip.
     
    Last edited: May 11, 2012
  4. Wendy

    Moderator

    Mar 24, 2008
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    Because electronics do the movement the AAC book uses electron flow. I made a post back with I was a regular member and Beenthere (a moderator who has deceased, and a good friend) put it up as a sticky in the Suggestions and Feedback forum. This is because we kept having people telling us we were wrong.

    Back when Ben Franklin was discovering electricity he had to flip a coin. It fell wrong side up. They had no concept of the true layout of matter, all they had were the concept of atoms, no electrons, protons, or neutrons. It took over 150 years for science to realize what they were actually looking at, but during that time an awful lot of textbooks had been written. Tradition is a hard thing to beat, and as concepts go it worked well.
     
  5. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    Ive hear this before. So if I choose actual flow then when I look at a published schematic, do I simply reverse everything in my mind when tracing the flow? For example, in the diagram I posted above, do I think of the electrons moving out of the negative side of the voltage source and into the Emitter of the NPN transistor and out the Collector? Where with Conventional flow, I would see electrons moving out the Cathode of the Diode and into the Collector of the NPN and out the Emitter...
     
  6. PatM

    Active Member

    Dec 31, 2010
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    For what it's worth - The US Army back in 1954 when I was in Field Radio Repair course was teaching electron flow.
    Later about 1978 I was teaching a General License class for Ham Radio, and actually had a "Licensed Engineer" scream at me because I was teaching the wrong theory.
    It makes no matter which method you use as long as you are consistent with the application.
     
  7. Wendy

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    Mar 24, 2008
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    I learned electron flow early, and never looked back. Conventional still exists because of all those text books I mentioned earlier, and it works.

    Wonder how that engineer explained tubes, given electron flow is fundamental to their operation? I've come across a lot of devices where this is the case.

    To me the arrow always points to the negative source, and the bar on the diode symbol is a dead end. Works for me.

    The funny thing is, this argument (discussion?) keeps repeating itself over and over, thread after thread. I tend to make people crazy because I say the same things over and over and over....
     
  8. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    I understand this gets brought up a lot, but I am asking if the function of the NPN transistors is reversed when thought of in "Actual Flow".

    In Conventional flow, electrons flow through the collector and out the emitter, but in Actual Flow, since electrons are coming from the negative terminal of the voltage source, are the roles reversed where the collector is the arrow and the emitter is what is sending electrons to the diode (the bar side)?
     
  9. Wendy

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    Mar 24, 2008
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    Don't forget there are two types for any particular transistor, such as BJTs have NPN or PNP. This means generalized statements go out the window concerning polarity, and the arrow still points to the negative with each.

    With many devices you learn the basic configurations. With BJT this means the Common Emitter configuration, which is used most of the time (but not all).
     
  10. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Well yes for the NPN transistor the emitter "emits" electrons.
    And collector "collects" those electrons.
    For PNP emitter "emits" holes and collector "collects" those holes.

    As for the current flow I prefer conventional current flow.
     
  11. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    Lets just say I am using a NPN BJT. Reference the picture I linked to in a previous post. With actual flow isn't the Collector really the Emitter and the Emitter is really the Collector?
     
  12. Jony130

    AAC Fanatic!

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    No, emitter always emits electrons in case of NPN transistor or holes in case of PNP transistor.
    Also collector always collect electrons/holes.

    In your circuit the electrons flow from negative battery terminal ---> emitter - collector-->LED---> 220R---> positive battery terminal
     
  13. #12

    Expert

    Nov 30, 2010
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    Don't even start thinking in terms of whether the collector collects and the emitter emits. You're setting a trap for yourself because that is inconsistent about whether you are using conventional (hole) flow or electron flow.

    Being consistent is the most important tool.
     
  14. fullNelson

    Thread Starter Member

    Nov 14, 2011
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    Ive mocked this same schematic up in Falstad's simulator. His flow shows electrons moving from the + side of the voltage source through the 220R into the LED and Through the collector and out the emitter into the - side of the source. To me this is Conventional flow.

    Is that right?
     
  15. Jony130

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    Yes the simulation show Conventional Current Flow from positive to negative terminal.
    Simply Conventional Current Flow show how positive charge flow.
    Electron flow show how a negative charge flow.
    And you should stick to Conventional Current Flow if you want to avoid confusion.
     
  16. Wendy

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    And are not using the AAC text book, whose links are on top of the page. Some folks like it.
     
  17. fullNelson

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    Nov 14, 2011
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    Does AAC "textbook" (took me a while to figure out you were talking about this sites tutorials lol) teach actual flow then?
     
  18. Jony130

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  19. Wendy

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    Electrons are what flow in wire, so I would define it as correct. Conventional flow works, but does not jive with physics, and the structure of an atom. This is why the argument keeps coming up, over and over and over.

    I agree being consistent is crucial. If your text book teaches conventional, that is what you need to use. You do have to understand the differences though, and be able to adjust mentally.

    All About Circuits has a text book built in, the volumes of the book are on the top of every page here. If you use it at all you have to understand electron flow. If you don't then it doesn't matter. It really is a personal choice.

    Generally though, when discussing electronics at this site, people will be talking electron flow because of our book. It was what got this site started.
     
  20. mlog

    Member

    Feb 11, 2012
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    I think it makes sense that current flows from high potential to low potential, i.e. positive voltage to negative voltage. The same is true for fluid flow, where fluids flow from high pressure to low pressure. I had originally learned on my own electron flow, but I was soon "corrected" when I entered into formal schooling.
     
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