BJT's Saturation Region

Discussion in 'Homework Help' started by khiawyen, May 5, 2009.

  1. khiawyen

    Thread Starter New Member

    Nov 17, 2008
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    Vce < Vbe will cause a BJT to be in saturation mode. How is it possible that Vce < Vbe will forward bias both the PN junction in a NPN transistor?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    63
    If Vbe is about -0.7V and Vce is about -0.3V then the base-collector diode (NP) will be forward biased. The collector is more positive than the base.
     
  3. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    Vbe+Vcb=Vce, hence Vbc=Vbe-Vce

    As an example, if Vce=0.2 V and Vbe=0.7V, then Vbc=0.5V which is forward biasing of the base-collector junction.
     
  4. steveb

    Senior Member

    Jul 3, 2008
    2,433
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    mik3,

    Did you misread his post and think that he said PNP transistor?
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Yes! :rolleyes:
     
  6. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    When Vce < Vbe a chunk of the collector current flows back through the base, which is one of the reasons why a transistors gain is so low in the saturation region.

    There is no universally agreed definition of saturation - Vce < Vbe is as good as any; another popular rule of thumb is Ic <= 10xIb.
     
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