Fundamentals of Electric Circuits

3.9 Applications: DC Transistor Circuits 111
For the BJT circuit in Fig. 3.43, and V BE 0.7 V. Find v o .
b 150 Example 3.13
Solution:
1 kΩ
1. Define. The circuit is clearly defined and the problem is clearly
stated. There appear to be no additional questions that need to
be asked.
2. Present. We are to determine the output voltage of the circuit
shown in Fig. 3.43. The circuit contains an ideal transistor with
b 150 and V BE 0.7 V.
3. Alternative. We can use mesh analysis to solve for v o . We can
replace the transistor with its equivalent circuit and use nodal
analysis. We can try both approaches and use them to check
each other. As a third check, we can use the equivalent circuit
and solve it using PSpice.
4. Attempt.
+
2 V
−
100 kΩ
Figure 3.43
For Example 3.13.
200 kΩ
+
v o
−
16 V
+
−
■ METHOD 1
Working with Fig. 3.44(a), we start with the first loop.
2 100kI 1 200k(I 1 I 2 ) 0
or
3I 1 2I 2 2 10 5
(3.13.1)
1 kΩ
+
2 V
−
+
2 V
−
+
100 kΩ
v o I 3
−
I 1 200 kΩ I2
(a)
1 kΩ
100 kΩ V 1 I B
150I B +
+
v o
200 kΩ 0.7 V
−
−
16 V
+
−
16 V
+
−
(b)
R1
700.00mV
14.58 V
R 3
100k
+
2 V
−
R2 200k
+
0.7 V
−
F1
1k
16 V
+
−
F
(c)
Figure 3.44
Solution of the problem in Example 3.13: (a) Method 1, (b) Method 2,
(c) Method 3.