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DC equivalent circuit of CB transistor?

  1. Mar 1, 2016 #1
    figure 1 shows dc model of CB transistor, why is it that collector diode is taken as current source in equivalent circuit, why not emitter is also taken as current source ?

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  3. Mar 1, 2016 #2


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    Generally the collector in any configuration is considered a current source provided there is an emitter resistor and a stable voltage on the base. The emitter resistor provides negative feedback. If too much emitter current is flowing the voltage across the emitter resistor rises which in turn reduces the base-emitter voltage and of course this moves the transistor slightly more towards off.
  4. Mar 2, 2016 #3


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    I rather think that the answer has nothing to do with an emitter resistor, which might be there or not.
    In CB configuration the OUTPUT is at the collector node - and the small-signal equivalent model shows the source that delivers an output "signal" at this node.
    And the "signal" is identical to a current (Ic).
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