# 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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0
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
43
Show us your attempt and if there is any problems someone will correct you.

3. ### circuitnass Thread Starter New Member

May 18, 2011
3
0
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 thanx