it remains only to calculate the base current,
obviously, the value of B critically affects the base current. note, however, that in this circuit the value of B will have no effect on the mode of operation of the transistor Since B is generally an ill-specified parameter, this circuit represents a good design. As a rule, one should strive to design the circuit such that its performance is as insensitive to the value of B as possible. The analysis details are illustrated in Fig. 4.19(b)./
Exercises
D4.15 for the circuit in fig. 4.19(a), find the largest value to which Rc can be raised while the transistor remains in the active mode.
Ans. 2.17k
D4.16 Redesign the circuit of fig. 4.19(a) (i.e., find new values for Re and Rc) to establish a collector current of 1 mA and a reverse bias on the collector-base junction of 4 V. Assume a = 1.
Ans. Re = 9.3 k ; Rc = 6 k /
Example 4.6
we want to analyze the circuit in fig. 4.20(a) to determine the voltages at all nodes and the currents in all branches. assume B=100. /
solution
the base-emitter junction is clearly forward-biased. Thus
Assume that the transistor is operating in the active mode. we now can write
the collector voltage can now be determined as
since the base voltage Vb is
it remains only to calculate the base current,obviously, the value of B critically affects the base current. note, however, that in this circuit the value of B will have no effect on the mode of operation of the transistor Since B is generally an ill-specified parameter, this circuit represents a good design. As a rule, one should strive to design the circuit such that its performance is as insensitive to the value of B as possible. The analysis details are illustrated in Fig. 4.19(b)./ExercisesD4.15 for the circuit in fig. 4.19(a), find the largest value to which Rc can be raised while the transistor remains in the active mode.Ans. 2.17kD4.16 Redesign the circuit of fig. 4.19(a) (i.e., find new values for Re and Rc) to establish a collector current of 1 mA and a reverse bias on the collector-base junction of 4 V. Assume a = 1.Ans. Re = 9.3 k ; Rc = 6 k /Example 4.6we want to analyze the circuit in fig. 4.20(a) to determine the voltages at all nodes and the currents in all branches. assume B=100. /solution the base-emitter junction is clearly forward-biased. ThusAssume that the transistor is operating in the active mode. we now can writethe collector voltage can now be determined assince the base voltage Vb is
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