Question 7.8: Determine the static value of current gain and collector vol...
Determine the static value of current gain and collector voltage in the circuit shown in Fig. 7.35.
Since 2 V appears across R4, we can determine the emitter current easily from:
I_E=\frac{V_E}{R_4}=\frac{2 \ V}{1 \ k\Omega } =2 \ mANext we should determine the base current. This is a little more difficult. The base current is derived from the potential divider formed by R1 and R2. The potential at the junction of R1 and R2 is 2.6 V, hence we can determine the currents through R1 and R2. The difference between these currents will be equal to the base current.
The current in R2 will be given by:
The current in R1 will be given by:
I_{R1}=\frac{9 \ V-V_B}{R1} =\frac{6.4 \ V}{68 \ k\Omega } =94.1 \ \mu AHence the base current is found from:
I_B = 94.1 μA − 79 μA = 15.1 μANext we can determine the collector current from:
h_{FE}=\frac{I_C}{I_B} =\frac{2.0151 \ mA}{15.1 \ \mu A} =133.45Finally we can determine the collector voltage by subtracting the voltage dropped across R3 from the 9 V supply.
The voltage dropped across R3 will be:
Hence V_C = 9 \ V − 4.43 \ V = 4.57 \ V