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Analogy about Transistor

Discussion in 'General Electronics' started by Animesh Maurya, Aug 30, 2003.

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  1. I have developed an analogy about transistor's amplification action.

    Consider an PNP transistor in Common-Base configuration.
    Emitter-Base region is forward biased and that of Collector-Base
    region is reverse biased.

    | | | |
    -------| P | N | P |-------
    | | | | | |
    | _________ __________ |
    | | |
    |+ =======>> | - |
    ----- | ---
    --- | -----
    |- | +|
    | | <<======== |
    | | |

    Now replace the transistor with a hollow cylindrical container.

    Place two porous membranes vertically opposite to each other at the
    centre of the cylinder and call the enclosed region as base.

    Distance between these two membranes is considered small as compared
    to the length of the cylinder due to the fact that base region is
    small in a transistor.

    A small hole in made on the body of the cylinder in the base region.
    Diameter of this hole is small than that of emitter & collector.

    Connect this assembly using tubes in Common-Base configuration and put
    pumps in place of a battery.
    Fill up the tubes with water. Assume that water flows in the same
    direction as that of the conventional current of battery (i.e. form
    +ve to –ve).

    Now put on the pumps and see what happens.

    Let us first highlight the Emitter-Base region.

    Water flowing form the emitter reaches the base and will start
    dividing. But majority of water will be transferred to the collector,
    as the base opening in very small.

    Moreover in Collector-Base region the pump is applying force which is
    just opposite to that of the base and thus making base current less
    and less, which in turns facilitates large collector current. This
    causes amplification.

    Analogies are seldom perfect and at times can be misleading. I don't
    know to which extent it is correct.

    Also one major drawback in that I cant explain amplification in case
    of a NPN transistor, if the above assumption are unaltered.


    Animesh Maurya
  2. Dana Raymond

    Dana Raymond Guest

    I heard somewhere that "Transistor" comes from Transference of Resistance.
    Just a datapoint.

    It seems to me that you could replace the transistor with a pair of
    resistors (one from emitter to base, and one from base to collector),
    and the same analogy would apply just as well. Your model needs more
    details before it explains anything. Charge carriers act very
    differently in a chunk of semiconductor with little electric field
    through it than they do in a chunk containing a large electric field.
    Think about which volumes are emptied of almost all charge carriers
    and biased with an electric field, and which volumes are flooded with
    charge carriers but have little electric field.
  3. DJ Bartlett

    DJ Bartlett Guest

    It's an amalgam of transducer and resistor

    just a datapoint 8 D.

  4. Dana Raymond

    Dana Raymond Guest

    Thats surprising since there is no aspect of a transistor that could be
    considered a transducer.

  5. zigoteau

    zigoteau Guest

    (Animesh Maurya) wrote in message
    Hi Animesh,
    I'm afraid your analogy is not very good and does not explain or
    reproduce any of the characteristic features of a transistor. How does
    it explain the rectification of the emitter-base junction and the
    base-collector junction? These depend intrinsically on the fact that a
    semiconductor has majority and minority carriers, aspects which a
    hydraulic model is totally incapable of mimicking.


  6. Does it resembles with the Eber Molls model ?

    Animesh Maurya
  7. Ian Stirling

    Ian Stirling Guest

    Very similar :)
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