ThevBaseCir - Thvenin Base Circuit Although the base is not...

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Thévenin Base Circuit Although the base is not an output terminal, the Thévenin equivalent circuit seen looking into the base is useful in calculating the base current. It consists of a voltage source v b ( oc ) in series with a resistor r ib fromthebasenodetos igna lground . F ig . 1(a)showstheBJT symbol with a Thévenin source connected to its emitter. Fig. 1(b) shows the T model for calculating the open-circuit base voltage. Because i b =0 , it follows that i 0 e =0 .Thu sth e r e is no drop across r x and r e so that v b ( oc ) is given by v b ( oc ) = v e = v te r 0 + R tc R te + r 0 + R tc (1) Figure 1: (a) BJT with Thevenin source connected to the emitter. (b) T model for calculating v b ( oc ) . The next step is to solve for the resistance seen looking into the base. It can be calculated by setting v te =0 and connecting a test current source i t to the base. It is given by
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This note was uploaded on 05/26/2011 for the course ECE 3050 taught by Professor Hollis during the Summer '08 term at Georgia Institute of Technology.

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ThevBaseCir - Thvenin Base Circuit Although the base is not...

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