5, Chapter Problem 8. Obtain vo for each of the op amp circuits in Fig. 5.47.
Figure 5.47 for Prob. 5.8 Chapter 5, Solution 8. (a) If va and vb are the voltages at the inverting and noninverting terminals of the op amp. va = vb = 0 1mA = (b)
10 k
0 - v0 2k
v0 = -2V
2V
+
ia
va
+ +
vo 2 k
2V +-
10 k
vb
1V +
+
va
+ ia
vo
(a)
-
-
-
(b)
Since va = vb = 1V and ia = 0, no current flows through the 10 k resistor. From Fig. (b), -va + 2 + v0 = 0 v0 = va - 2 = 1 - 2 = -1V
1
Chapter 5, Problem 10. Find the gain vo/vs of the circuit in Fig. 5.49.
Figure 5.49 for Prob. 5.10
Chapter 5, Solution 10. Since no current enters the op amp, the voltage at the input of the op amp is vs. Hence
10 v o vs = vo = 10 + 10 2
vo =2 vs
2
Chapter 5, Problem 13.
Find vo and io in the circuit of Fig. 5.52.
Chapter 5, Solution 13.
10 k a b 1V + - 90 k + - io
100 k i2
i1 10 k
+ vo
50 k
-
By voltage division, va =
90 (1) = 0.9V 100
v 50 vo = o 150 3 v0 vo = 2.7V But va = vb 0 = .9 3 v v io = i1 + i2 = o + o = 0.27mA + 0.018mA = 288 A 10k 150k
vb =
3
Chapter 5, Problem 20.
In the circuit in Fig. 5.59, calculate vo if vs = 0.
Figure 5.59
Chapter 5, Solution 20. 8 k
4 k
a
4 k
2 k b
- +
+ vo
9V
+ -
vs
+ -
-
At node a,
9 - va va - vo va - vb = + 4 8 4
18 = 5va vo - 2vb
(1)
At node b,
va - vb vb - vo = 4 2
va = 3vb - 2vo
(2)
But vb = vs = 0; (2) becomes va = 2vo and (1) becomes -18 = -10vo vo vo = -18/(11) = -1.6364V
4
Chapter 5, Problem 26.
Determine io in the circuit of Fig. 5.64.
Figure 5.64
Chapter 5, Solution 26.
+ vb + 0.4V + 8k 2k vo 5k io
vb = 0.4 = Hence,
8 vo = 0.8vo 8+ 2
vo = 0.4 / 0.8 = 0.5 V
io =
v o 0 .5 = = 0.1 mA 5k 5k
5
Chapter 5, Problem 38.
Calculate the output voltage due to the summing amplifier shown in Fig. 5.75.
Figure 5.75
Chapter 5, Solution 38.
R R R R v o = - f v1 + f v 2 + f v 3 + f v 4 R2 R3 R4 R1 50 50 50 50 = - (10) + (-20) + (50) + (-100) 20 10 50 25
= -120mV
6