Confusion regarding ideal current sources

Discussion in 'General Electronics Chat' started by johnmariow, May 4, 2016.

  1. johnmariow

    Thread Starter New Member

    May 4, 2016
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    I have seen where constant current sources can create a lot of confusion among people learning electronics because different books have different definitions of the constant current source symbol.

    Consider a constant current source symbol containing an arrow that points from left to right. If we assume that the arrow shows the direction of electron flow, then the current would be flowing from left to right. In the attached schematic, the polarity of the voltage across the resistor would be positive on the left side of the resistor and negative on the right side of the resistor because electrons flow from negative to positive.

    However, if the arrow in the constant current source symbol represents the conventional flow of current from positive to negative, then the arrow shows the direction of the flow of holes. Accordingly the polarity of the voltage across the resistor would be the opposite of that described in the above paragraph.

    If the reader buys a book about electronic theory, keep in mind that the arrow inside the constant current source symbol represents the direction of the flow of holes; Not the direction of the flow of electrons.

    One can prove this by using the LTSPICE simulator.

    Has anyone else come across this type of error? All comments are welcome. Constant Current Source.JPG
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Not again with this. The international system of units calls for conventional current flow. Period, end of story.

    If you find a text using electron flow or some other nonsense leave it on the bookshelf and get a real book.

    How I wish the mods would now close this thread.

    (Hi John, welcome to the forums!!!)
     
  3. johnmariow

    Thread Starter New Member

    May 4, 2016
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    Thanks for your reply. I've found many electronics books that should have been left on the book shelf because the contents were obviously not proof read. One text book I purchased for a course had a small pamphet in the back of the book listing all the errors in the book and showing the corrections for those errors. By the way, I searched and did not find any posts regarding this specific topic. If I did, I would not have posted this.

    Best regards,
    John
     
  4. ErnieM

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    Apr 24, 2011
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    Threads on this appear with surprising regularity here as there are not a few people who think electron flow is in some way superior or conventional current does not explain the physical world as we know it. For example they will talk about how vacuum tubes cannot be explained by conventional current.

    People with such beliefs may have other bad habits.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    The arrow shows conventional direction, end of story. Just like a battery symbol has one end unambiguously positive, or a diode looks like a na arrow pointing in the direction of conventional current, you cannot just say that what is in the schematic actually means the opposite of what everyone knows.
     
  6. johnmariow

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    May 4, 2016
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  7. johnmariow

    Thread Starter New Member

    May 4, 2016
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    I have a reference manual that implicitly assumes electron flow which is the reason why I created this post. One would think the mistake would be corrected in the second edition of the manual. I also have an electrical engineering handbook with an error in it. Glad I only paid several dollars for it.
     
  8. BR-549

    Well-Known Member

    Sep 22, 2013
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    Conventional flow is a mathematical equality that is used to analyze and design.

    It's ok. It works. It won't hurt you. Don't be afraid of it. Most symbols now will show it.

    BUT.........neither positive charge OR whole charge............flows. A whole is an empty space. There is nothing in it that can be moved. Protons (real positive charge) are held in place by the "strong nuclear force". You will not be moving them.

    Positive and whole flow is a mathematical abstract.

    Many educated people believe this abstract is real. Let them live with it. Let them teach it. Let them explain it. Then agree with them.

    And then find someone else to learn from.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    I don't recall seeing a constant current source symbol in which the arrow represented the direction of electron flow -- but then I quickly close books that insist on using electron flow because I have yet to find one that doesn't rely on magical mystery minus signs to correct their inconsistent math. To my mind, that is by far the bigger problem.

    There are similar notational differences that lead to confusion that have nothing to do with conventional versus electron current. The most common one is using an arrow to indicate voltage polarity. Some parts of the world point the arrow toward the more positive voltage and others do exactly the opposite. Far better (again, to my mind) to simply use a plus and/or minus sign at the appropriate end(s).
     
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  10. neonstrobe

    Member

    May 15, 2009
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    Transistors would not work if we did not have hole flow. "Hole flow" might really be electrons "flowing the other way" as it describes a mobile positive charge through the interaction of electrons with atomic crystal structure.IN good old tungsten lamps Hall voltage shows that positive charges are moving so the concept should be accepted. However convention has remained with us for 100 years that current flow is + to -. I don't think that will change any time soon.
     
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  11. ErnieM

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    Apr 24, 2011
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    I'm glad you get it.

    As you can see from the post directly following yours the confusion that exists where people cannot separate the definition of current from a particular example of a current, plus a (rather obvious to me) mathematical mistake or oversight in the magnitude (sign) of that current.

    As current is one of the seven base standard measurement units (Wiki International System of Units) it is essential to carry the correct definition in your head.
     
    Last edited: May 4, 2016
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  12. johnmariow

    Thread Starter New Member

    May 4, 2016
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    The polarity of the voltage across the resistor was also wrong in the case I mentioned. The same error existed every example the author provided in the whole chapter. My solution was to note the error and use the LTSPICE circuit simulator to yield the correct solution to each example presented by the author.
     
  13. ronv

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    Nov 12, 2008
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    I'm trying to figure out if I care. :oops:
     
  14. ElectronicMotor

    Member

    May 1, 2016
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    Hi guys

    This is an interesting topic. The circuit shown can be used to produce millions of Volts and Amps simultaneously, as long as it is switched at a critical resonant frequency.

    Constant Current Source.jpg


    The switched constant current source is a photo-transistor, and has a very small value, in micro-Amps, but can ring this circuit until the resistor limits everything to some desired exponential ring-down frequency.
    I found that on a Spice simulator I could get 12,000 Volts Peak to Peak or +6,000 Volts to -6,000 Volts ringing across the capacitor, using some typical values.
    OK. I'll buy a constant current source and Bobs your uncle.
    After chatting with some very clever people, this is easier said than done.
    While the NPN transistor is on, and current is flowing from collector to emitter (c-e), and the voltage across the c-e junction is forward biased at +6,000 Volts, 100,000 Amps will flow. Easy enough, that's fair.
    But when the constant current source needs to supply 100,000 amps when the c-e junction is biased on the negative half-cycle of -6,000 Volts,
    the c-e junction now not only needs to supply +6,000 Volts to oppose the -6,000 Volts on the terminals, but another +6,000 Volts and 100,000 Amps to keep the sine wave resonating above and below zero, and keep the current in the constant current source flowing in one direction and at one value.
    That is why a constant current source is rather cool, but difficult to find ?
     
    Last edited: May 5, 2016
  15. #12

    Expert

    Nov 30, 2010
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    Schematics are drawn in several countries and this has been going on for about a century. Just figuring out the symbols peculiar to one country or one decade or one corporation is enough of a challenge for me. I spend my OCD budget on understanding the circuit, not on claiming the author must be wrong because he didn't do it the way I prefer. That's probably why I can think in either kind of current flow, as necessary.

    Are you an electronics nerd or a proof reader?
    Oh, by the way, picking one is an option.;)
     
    Last edited: May 5, 2016
  16. WBahn

    Moderator

    Mar 31, 2012
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    That pamphlet is know as an errata sheet and virtually every textbook has one and the better textbooks tend to have longer errata sheets. This is primarily a result of more people using the text and looking at it more closely and reporting them and then the author/publisher doing a more diligent job of taking those reports and updating the errata sheet. No work as large as a textbook is going to be error free. Its the texts that don't provide an errata sheet that you really need to worry about.

    Now, just being willing to provide a comprehensive errata sheet doesn't make up for fundamentally poor coverage of the material, so don't read more into this than is there.
     
  17. ElectronicMotor

    Member

    May 1, 2016
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    Buying from China is Good and Bad, Ying and Yang.
    It is good, because it is cheap.
    It is bad, because they don't supply data sheets. :(
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    What on earth does any of this have to do with textbooks and current conventions applied to ideal current sources?
     
  19. BR-549

    Well-Known Member

    Sep 22, 2013
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    The thing that conventional current people and electron current people have in common, is that we all get tired of talking about it.

    People love to argue. But do not like arguing about the same thing.

    Let's find something new to fight about.

    How about that dumb-ass gravity experiment. ha ha
     
  20. WBahn

    Moderator

    Mar 31, 2012
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    But we also have to keep in mind that it is not the same old thing for the people asking about the same old things. To them it is a very new and relevant and confusing issue. No one is requiring anyone that is tired of it respond or even read the thread once they see that it is the same old thing.
     
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