opamp current direction in e-book

Discussion in 'General Electronics Chat' started by swty_todd, Mar 26, 2009.

  1. swty_todd

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    Aug 3, 2008
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  2. thatoneguy

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    Electrons/electricity are negative, so they flow towards a more positive potential.

    Often, you can look at "conventional current" as "hole flow", which goes from positive to negative. In reality, the electrons are going the other direction.

    The most important aspect is to follow the same convention in any single circuit.
     
  3. swty_todd

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    They have shown the electron flow and not the hole flow , right?
     
  4. Wendy

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    Mar 24, 2008
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    Electron flow is the norm nowdays. Unfortunately conventional flow theory lasted long enough to help dictate how components were drawn. They would have been slightly more intuitive otherwise.
     
  5. thatoneguy

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    Yes. Both formats/methods are still seen, which causes much confusion. The arrows on semiconductors pointing "the wrong way", as Bill noted above, don't help clear up the issue, either.
     
  6. beenthere

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    Apr 20, 2004
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    With respect to holes, they are a construct to explain current in semiconductors. The only animals you find loose in wires are electrons. They carry a negative charge, and so current is a movement of electrons.
     
  7. sohcahtoa

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    Nov 7, 2006
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    It really is enough to drive one out of one's skull at times. Conventionally, the way they've drawn it is -6mA (hole flow).

    Is electron flow really the norm right now? I'm currently an EE student, and we've only dealt with circuit diagrams using the conventional method. At first, I thought using electron flow would be much more intuitive, but now I'm so used to the conventional model I don't question it any more.
     
  8. swty_todd

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    I may be dumb but i dont get this " arrows on semiconductors pointing the wrong way" (which arrows)??
     
  9. thatoneguy

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    In an NPN transistor schematic symbol, the arrow is pointing "out" of the emitter, when actually, this is where the current enters.
     
  10. peajay

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    Dec 10, 2005
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    It's like this: [A]-----[component]-----

    Which of these two makes more sense:

    Positive current flowing from A to B will cause the voltage at B to rise.

    Positive current flowing from A to B will cause the voltage at B to fall.

    The former statement uses conventional terms. If the component is a 2 ohm resistor, and point A is +1 volt, and point B is -1 volt, then the current flow from point A to point B is +1 ampere, and this positive current flow will increase the voltage at its destination and decrease the voltage at its source, just as you would expect a positive value leaving one point and arriving at another point to do.

    If we start talking about electron current instead, then it no longer makes sense. We then have a negative current flow from A to B, but this negative current flow to B causes B to become more positive. So now whenever we do any sort of math we have to remember to constantly reverse/negate everything so that the calculated voltages and currents are correct.

    Yes, it seems silly to say that the current is flowing in the direction opposite the way the electrons are flowing, but that's because "current" isn't defined as "electrons" just as "voltage" isn't defined as "electrons." After all, when we put more electrons somewhere, we don't say that point now has more voltage, because we know that electrons are not voltage.

    I guess people understand that last point because electrons have negative charge, and so it is undeniable that voltages are lower where there are more electrons. What I don't get is why it is so hard to understand that so long as electrons are anti-voltage, they are necessarily anti-current as well, and so when the electrons flow one way, the current flows the other way, just like when the population of electrons at a point rises, the voltage at that point falls.

    All you have to do is realize that electrons are not current and electrons are not voltage, nor are electrons power or energy. Electrons are charge, and they're negative charge at that, so just forget about them until you're far enough into electronics to be discussing advanced topics like charge, and then, so long as you remember that they are negative charge, it'll all make perfect sense with conventional current flow. You'll realize that negative charge flowing one direction is equivilent to positive charge flowing the other direction. You'll then realize that negative charge flowing in one direction must mean a negative current is flowing in that direction, because if it were a positive current, then when a positive charge flows in that same direction, it would be a negative current, which doesn't make any sense.
     
  11. Ratch

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    Mar 20, 2007
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    swty_todd,

    Because the diagram is not using the conventional charge method of designating charge flow. Instead of always assuming that the positive charge travels from the positive side of the voltage source, it is trying to use the actual movement of the charge carriers (electrons) to designate the direction of the current. That will become very confusing when you encounter true positive charges such as positive ions in electrochemistry and positive holes in P-type semiconductor material. No holes exist is wires, by the way. I expounded on this in this link
    http://forum.allaboutcircuits.com/showthread.php?t=21280

    You are not dumb, only confused. Look at the specifications of a diode. They show a arrow pointing into a bar. The arrow designates the direction of conventional current. That means that if you put a positive voltage on the arrow side and a negative voltage on the bar side, you will cause a current to exist. Now remember, a positive charge going in one direction is equivalent to a negative charge (electrons) going in the opposite direction.

    Ratch
     
  12. Ratch

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    Mar 20, 2007
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    thatoneguy,

    If you hook up a ammeter to the transistor emitter, you will see that the current direction agrees the schematic arrow.

    Ratch
     
  13. Ratch

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    Mar 20, 2007
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    sohcahtoa,

    It sure wasn't when I went to school. Just remember, trying to keep track of current direction by the movement of the actual charge carriers will lead to confusion. That is because in some cases positive charge carriers also move, and that will conflict with what you assumed for negative charge carriers. The reason the engineers developed a convention for current was to obliterate the need to worry about the polarity of the charge carriers and the direction they "really" move.

    Ratch
     
  14. Ratch

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    Mar 20, 2007
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    peajay,

    With repect, your last posting is very confusing. First of all, current does not flow. Instead charge flows. As I said many times before, "current flow" means "charge flow flow".

    Have you read this link? http://forum.allaboutcircuits.com/showthread.php?t=21280 . If you want to talk about confusion, just use the direction of the "real" charge carriers to designate the current direction. There are two different charge carriers, so you have two different directions to worry about.

    Ratch
     
  15. Dave

    Retired Moderator

    Nov 17, 2003
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    Please see the relevant section in the e-book.

    Note it states the authors intentions:

    Dave
     
  16. peajay

    Well-Known Member

    Dec 10, 2005
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    With repect, your last posting is very confusing.

    It must have been confusing as I believe we are in agreement on the issue.

    First of all, current does not flow.

    Perhaps the best solution is to stop using the arrows since the current isn't going anywhere anyway. We just need a new symbol to indicate the polarity of the current measurement. Perhaps we could use an arrow and we could point it in the direction that positive charge would flow with respect to a positive current. That should clear everything up. :)
     
  17. swty_todd

    Thread Starter Active Member

    Aug 3, 2008
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    I should have read that.:)
     
  18. thingmaker3

    Retired Moderator

    May 16, 2005
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    Current is most often defined as "a flow of moving charge carriers." For the purposes of the AAC textbook (and many many other texts as well) those charge carriers are electrons. http://www.allaboutcircuits.com/vol_1/chpt_1/2.html

    Some texts still prefer to reference the charge carriers as holes, or to define current as a field flow. It is important to realize different definitions exist. It is important to know which definition is used in the venue in which a discussion is taking place. Otherwise, pointless argument results over the definition of "definition."
     
  19. thatoneguy

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    Feb 19, 2009
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    True, I posted in the other thread that it doesn't really matter unless you are working with quantum mechanics or masking semiconductors, where positive to negative doesn't work out as well.
     
  20. Ratch

    New Member

    Mar 20, 2007
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    peajay,

    What do you mean by current not going anywhere? Current can be measured thousand of miles from its voltage source. You already have a symbol to indicate the polarity of the measurement. Every voltmeter and ammeter has its leads marked to indicate how it will display the direction of the current.

    That has already been done. It is called conventional current direction. And yes, it already clears everything up, unless you want to confuse yourself with electron flow.

    Ratch
     
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