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real working of transisitors

Discussion in 'General Electronics' started by sanjoealex, Jul 8, 2004.

  1. sanjoealex

    sanjoealex Guest

    Usually we say atransistor is in saturation when its collector-base jn
    and emitter basejunction are forward biased.But if CB jn is forward
    biased,the current should flow as in a diode but it doesn't. The
    transistor should behave as if two diodes are kept in opposite
    direction.But it doesn't.Why???? Can somebody help me with this?
     
  2. Ben Moss

    Ben Moss Guest

  3. sanjoealex

    sanjoealex Guest

    But still i can't get an answer to my question. I have searched many
    textbooks and sites and still i couldn't find an answer. My doubt is
    that the current in CB junction of a transisitor doesn't flow as in a
    diode even though the collector base junction is forward biased. Why
    is this so......???? The sites which were listed here didn't provide
    me with the required information.
     
  4. Rich Grise

    Rich Grise Guest

    That's because nobody does what you're asking about. The thing you're
    looking for is meaningless, unless you're using the transistor in
    upside-down mode, and there has been no indication that you even have
    a clue what that is.

    In normal operation, the collector-base junction is reverse
    biased. Current through the base-emitter junction influences
    the flow of current from emitter to collector (or from collector
    to emitter, depending on your POV), such that it amplifies. So
    the collector-base junction isn't even _supposed_ to act like
    a diode.

    If you hook the transistor in upside-down mode, swapping the
    collector and emitter, then the base-collector junction will
    be forward-biased, and will act very much like an ordinary
    diode, and in many cases, the transistor will even transist,
    but it's generally not recommended to try to use them that
    way unless the transistor was designed for it.
     
  5. sanjoealex

    sanjoealex Guest



    But even then the transistors used in switching purposes(in the
    manufacture of gates for eg:) do enter into the saturation mode where
    both the CB and BE junctions are forward biased. What will happen
    there??? Will the CB junction conduct the way a forward biased diode
    conducts????????
     
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