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NPN BJT in reverse active mode - base current direction

  1. Feb 21, 2015 #1

    etf

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    • Warning: Template missing in homework help request.
    Hi!
    I was wondering what happens with Base current direction if NPN BJT works in reverse active mode? In forward active and in saturation mode currents are like this:

    for.png

    Collector and emitter currents in reverse active mode would be in opposite direction:

    inv.png :
     
  2. jcsd
  3. Feb 21, 2015 #2

    phyzguy

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    Science Advisor

    In this case base current would be flowing from the base into the collector. So it would still be flowing into the base, but instead of flowing out of the emitter it would be flowing out of the collector.
     
  4. Feb 21, 2015 #3

    etf

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    Is it possible for base current to flow in opposite direction, like this:

    inv.png

    ?

    Here is example from Multisim:

    Untitled.jpg
     
  5. Feb 21, 2015 #4

    phyzguy

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    No. Forward active mode means the emitter/base junction is forward biased. Reverse active mode means the collector base junction is forward biased. In both cases current is flowing into the base. In order for current to flow out of the base, it has to be flowing through a reverse-biased junction. This means the junction is in breakdown, which typically destroys a bipolar transistor. Multisim may show it happening, but if you try it on a real device you will fry it.
     
  6. Feb 21, 2015 #5

    etf

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    One definitelly shouldn't trust to simulation software 100% :)
    You helped me a lot, thanks!
     
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