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Equivalent Operating CircuitAuthor: Leonard Krugman Fig. 39. Equivalent circuit for grounded base connection. At this point, the transistor equivalent circuit must be considered using a practical circuit, such as illustrated in Fig. 39. The signal generator E_{g}, having an internal resistance R_{g}, is connected between the emitter and the base. Input loop 1:
Output loop 2: r_{m}i_{e} = i_{1}r_{b} + i_{2} (r_{c} + r_{b} + R_{L}). Since i_{e} = i_{1}, then
Since these two loop equations are independent, they may be solved simultaneously for the two unknown currents i_{1} and i_{2}. Then
Under ideal conditions, namely, when R_{g} equals zero, and R_{L} is infinite, it was previously found that r_{11} = r_{e} + r_{b}, r_{12} = r_{b}, r_{21} = r_{b} + r_{m}, and r_{22} = r_{c} + r_{b}. If these values are substituted in equations 33 and 34, i_{1} and i_{2} can be evaluated in terms of the ideal or opencircuit parameters.


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