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Homework Help: Bipolar Junction Transistor

  1. Dec 8, 2009 #1

    Air

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    I've got these two BJT circuits. I want to know if the result are the same. Are both circuits below same? Can the bottom left resistor be grounded and be same as the second circuit.

    http://img21.imageshack.us/img21/2886/bjtt.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 8, 2009 #2

    berkeman

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    Staff: Mentor

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    Yes, they both go to ground, so the circuit can be drawn either way.
     
    Last edited by a moderator: May 4, 2017
  4. Dec 8, 2009 #3

    Air

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    Thank you.

    Also, if the bottom left resistor branch didn't exist, then the current in the emitter would just be the current in the collector plus the current in the emitter?
     
  5. Dec 8, 2009 #4

    berkeman

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    Staff: Mentor

    Not exactly, and I think you made s small typo anyway. The emitter current in this configuration is always the base+collector currents.

    If the lower left resistor is not there, then the base bias current is set by the upper left resistor and the supply voltage (Vs-Vb/R = Ibias). With the lower left resistor there, the bias is set more by a resistor divider effect, and will be a bit less temperature sensitive in terms of the base bias current versus temperature (Quiz Question -- whi?).
     
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