relation between collector current and collector voltage

Discussion in 'General Electronics Chat' started by sharmaarvind447, Nov 11, 2013.

  1. sharmaarvind447

    Thread Starter New Member

    Nov 8, 2013
    1
    0
    Dear All,

    Can anyone explain me the mechanism of collector current independence on collector base voltage in common base transistor in its active region?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    A BJT transistor acts like a current generator and has a high impedance in the active (not saturated) region. Typically this impedance is several tens of kohms or more depending upon the operating point. Thus the collector current does not vary greatly with the collector voltage. It's typically give as the conductance value Hoe in the data sheet (the inverse of resistance).
     
  3. LvW

    Active Member

    Jun 13, 2013
    674
    100
    What do you mean? Collector voltage (head line) or base voltage (text)?
    Please bear in mind that a voltage exist BETWEEN two points. That means: Neither the collector nor the base have a voltage, rather we speak about the collector-emitter and the base-emitter voltage.
    I suppose, you mean (as indicated in the head line) the relation between Ic and Vce.
    In addition to crutschow`s answer I can say the following:
    The current Ic is (mainly) determined by the base-emitter voltage Vbe.
    And - as long as there is a voltage Vce which is large enough (approx. >1 Volt) to keep the base-collector pn junction off, this current Ic can flow - relatively independent on the actual value of Vce. Don`t forget that the BJT is no resistor and Ohm`s law does NOT apply.
     
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