Different small signal equivalent circuit

Discussion in 'General Electronics Chat' started by samy555, Sep 13, 2014.

  1. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Hello

    "Semiconductor Devices and Basic Applications " page 435, the booktalks about:

    [​IMG]

    [​IMG]

    Figure 6.63 (b) is the small signal equivalent circuit. Notice that the dependant current source directed from the collector to the emitter.

    In other pdf file I found in:

    http://www1.i2r.a-star.edu.sg/~ongmichael/Chapter67.pdf


    On page 137 the following small signal equivalent circuit:

    [​IMG]

    Here the dependant current source directed from the Base to the Collector.

    My question: Is these MODELS are equivalent? If yes, how?

    Thank you
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    782
    In the first document note that V_\pi is equivalent to Vbe. In the second document V is Veb. Hence the source direction reversal is consistent with the opposite polarity notations for the controlling parameter.

    However, the source should presumably still be located between emitter & collector rather than base & collector.
     
  3. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    thank you
    please take a look on:
     
  4. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Thank you all
    I have discovered the reason for this discrepancy
    The reason is that one of them using the hybrid pi model, where the other using the T model
    please look at the attached file
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    782
    Good point.
    One would also have to make the distinction that \text{r_\pi \ and \ r_i } as shown in the two equivalent circuits aren't the same.
     
    samy555 likes this.
  6. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Yes, I agree entirely with you
    Thank you t_n_k
     
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