common-base BJT circuit

Discussion in 'The Projects Forum' started by circuitnass, May 18, 2011.

  1. circuitnass

    Thread Starter New Member

    May 18, 2011
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    In the circuit seen in the attachment , can you please help me write the KVL equation around the base-emitter loop (assuming the transistor is in forward-active mode)?
     
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  2. jegues

    Well-Known Member

    Sep 13, 2010
    735
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    Show us your attempt and if there is any problems someone will correct you.
     
  3. circuitnass

    Thread Starter New Member

    May 18, 2011
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    ok the book says that its;

    V+ = I<EQ>*RE + VEB(on) + (IEQ/(1+β))*RB

    now i dont get where (IEQ/(1+β)) came from

    my own attempt was V+ = I<EQ>*RE + VEB(on) + I<BQ>*RB
     
  4. jegues

    Well-Known Member

    Sep 13, 2010
    735
    43
    Your KVL is correct, and identical to the one given by your book.

    They simply rewrote Ib in terms of Ie.

    I_{b} = \frac{I_{c}}{\beta} = \frac{\alpha I_{e}}{\beta}, \quad \text{where, } \quad \alpha = \frac{\beta}{\beta + 1}

    \Rightarrow I_{b} = \frac{I_{e}}{\beta + 1}
     
  5. circuitnass

    Thread Starter New Member

    May 18, 2011
    3
    0
    oh yup ur ryt i get it now :D thanx
     
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