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Why is the reverse collector current ICBO taken as negative?

Discussion in 'General Electronics Discussion' started by help, Jun 10, 2010.

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  1. help


    Jun 10, 2010

    could any one post the reply for this fundamental question?

    Why is the reverse collector current ICBO ( minority current flowing between the collector base junction) taken as negative( in most of the standard textbooks) even though its direction is same as the majority carrier collector current for a Bipolar junction transistor( both npn and pnp)
  2. help


    Jun 10, 2010
    to make the question more clear

    When a pnp transistor is properly biased i.e EB is forward and CB is reverse biased.
    The current due to he holes from emitter crosses the base and reach the collector and flows from left to right ( i.e IPC flows to the right). The minority carriers in the reverse biased collector base junction i.e the holes in the n type base and the electrons in the p type collector move to the right and left respectively and hence there is a net saturation current ICBO flowing to the right. Hence my query is shouldn't the net collector currrent be IC=-(IPC+ICBO) rather than IC=-(IPC-ICBO) as given in most textbooks.

    In short why is ICBO which actually contribute additively to the majority hole current (IPC) be treated as a quantity which is in opposition to the majority hole current.
  3. tahir4awan


    Nov 29, 2010
    You are right. The IC=-(IPC+ICBO is valid.
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