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Great explanation of a transistor!

Discussion in 'General Electronics Discussion' started by mypcbis$crewed, Jul 3, 2010.

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  1. mypcbis$crewed

    mypcbis$crewed

    58
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    Nov 29, 2009
    Hello all, I wanted to contribute to this site that has helped me out quite a bit. I found this article to have a rather interesting take on how a transistor actually works inside. Heady stuff, but if you want to know what goes on in that black box, this is for you:

    http://amasci.com/amateur/transis.html
     
  2. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Ok, so I read that entire article but I am still confused on one aspect that this author doesn't seem to explain to me.

    You got the P-type base region and the N-type emitter region. when you take a P and N type material and stick them together they form a depletion region. I get that I took chemistry, I understand what it means to have free electrons in one atom and another atom that needs electrons. The basis for chemical reactions as I recall.

    But what I don't get is how adding in more electrons to the N type region causes the depletion region to get 'thinner' it would seem to me that the depletion region would just shift further into the base. As one added more electrons to the N side of the depletion region then those electrons would just move toward more holes in the P-type region causing the depletion region to either shift into another area(of the base region) or grow larger.

    Now taking this authors word that the depletion region thins makes the rest of his explanation of how a transistor works seems simplistic to say the least, but even then I still don't seem where his explanation is bullet proof and I certainly can see room for improvement. Anyone here like to teach this idiot(me) how the depletion region thins when a voltage potential is applied across the BE junction?

    EDIT: I think I answered my own question. http://en.wikipedia.org/wiki/P-n_junction
    For one, the p-n junction is a single piece of silicon. Two, the depletion area narrows because the electrons and holes are repelled toward each other when the voltage applied to the junction is forward biased. This is what causes the depletion layer to 'thin'.
     
    Last edited: Jul 3, 2010
  3. Jaderman

    Jaderman

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    Dec 12, 2009
    Thanks! Already printed it out and gonna put it on my "List to Read". I've been feeling the same way like he is. I've been trying to find a decent description and hopefully this will do!
     
  4. mypcbis$crewed

    mypcbis$crewed

    58
    0
    Nov 29, 2009
    Awesome isn't it! :D:D:D:D
     
  5. Dereklee

    Dereklee

    7
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    Jul 14, 2010
    yep, thanks for sharing, man.
    and it is wise to print it out. :)
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    It may be a great explanation, but does it help you design something using a transistor?

    My take is that many of the things he dismisses, whilst possibly not required to understand what a transistor does, nevertheless come in VERY handy if you want to design something using one.

    My major complaint in this vein is that he states that bipolar transistors are voltage rather than current devices. Whilst this may be true, the fact that the main controlling voltage appears across a forward biased diode junction renders this moot when faced with the actual use of the device.

    People who work on the basis of the device being voltage controlled often come up with amazingly wrong results by plugging in values like "5" into the base-emitter voltage (see here).

    If you rely on simple relationships like base vs. collector current then you risk less stupid results as a base current of several hundred amps is obviously not quite correct.

    So whilst that may not explain *why* or *how* the transistor works, it is a really good model for basic design using a bipolar transistor.
     
    Last edited: Jul 24, 2010
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