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ENGR-4300
Test 4B
Fall 2006
ENGR-4300
Fall 2006
Test 4B
Name ________________________
Section ________________________
Question 1 (20 points) ___________required
Question 2 (15 points) ___________required
Question 3 (17 points) ___________required
Skip one of the following questions. Indicate which question doesn’t count or else
questions 4 through 11 will be graded.
Question 4 (6 points) ___________
Question 5 (6 points) ___________
Question 6 (6 points) ___________
Question 7 (6 points) ___________
Question 8 (6 points) ___________
Question 9 (6 points) ___________
Question 10 (6 points) ___________
Question 11 (6 points) ___________
Question 12 (6 points) ___________
Total (100 points): ______________
On all questions: SHOW ALL WORK. BEGIN WITH FORMULAS, THEN
SUBSTITUTE VALUES AND UNITS. No credit will be given for numbers
that appear without justification. Answer the first 3 questions and 8 out of the
remaining nine 6-point questions.
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ENGR-4300
Test 4B
Fall 2006
Question 1 – Diode Circuits (20 points)
V
You are building a full-wave rectifier but in error you put in diode D3 backwards as in the
following circuit. Assume the diodes are ideal (Von = 0 V). The input sine wave has an
amplitude of 5 V and Vout is the difference voltage between the V+ and V- probes.
D1
V+
1
V-
R1
D3
R2
V1
VAMPL = 5
FREQ = 1kHz
10k
D4
D2
a) What is the maximum current that can ever flow through R2? (4 pts)
b) Sketch V1 and Vout. (5 pts)
8.0V
4.0V
0V
-4.0V
-8.0V
0s
0.2ms
0.4ms
V(V2:+)
V(R2:2)
0.6ms
0.8ms
1.0ms
Time
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1.2ms
1.4ms
1.6ms
1.8ms
2.0ms
ENGR-4300
Test 4B
Fall 2006
V
c) The TA spots your problem and removes D3 as shown below. With nothing else changed,
sketch V1 and Vout on the axis below. Again assume all diodes are ideal. (5 pts)
D1
V+
1
V-
R1
R2
V1
VAMPL = 5
FREQ = 1kHz
10k
D4
D2
8.0V
4.0V
0V
-4.0V
-8.0V
0s
0.2ms
0.4ms
V(V2:+)
V(R2:2)
0.6ms
0.8ms
1.0ms
1.2ms
1.4ms
1.6ms
1.8ms
2.0ms
Time
V+
D1
V-
V
d) The circuit is modified as below with R1 removed and the diodes modeled more
accurately with Von = 1V. Sketch V1 and Vout on the axis below. (6 pts)
R2
V1
VAMPL = 5
FREQ = 1kHz
10k
D4
D2
8.0V
4.0V
0V
-4.0V
-8.0V
0s
0.2ms
0.4ms
V(V2:+)
V(R2:2)
0.6ms
0.8ms
1.0ms
Time
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1.2ms
1.4ms
1.6ms
1.8ms
2.0ms
ENGR-4300
Test 4B
Fall 2006
V
V
Question 2 – Zener Diode Circuits (15 points)
V2
R1
1k
A
R2
10Meg
V1
VAMPL = 5
FREQ = 1kHz
B
For the circuit shown, a single device is in the box between points A and B. The time plots of
the input and output voltages V1 and V2 are shown below.
V1
5.0V
0V
V2
-5.0V
0s
V(V2:+)
1.0ms
V(R4:2)
2.0ms
3.0ms
4.0ms
Time
a) What type of device is in the box? (3 pts)
b) Draw the device’s correct orientation between points A and B below. (3 pts)
A
B
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5.0ms
ENGR-4300
Test 4B
Fall 2006
c) By the plot above, what is Von for the device? (3 pts)
d) By the plot above, what is the breakdown voltage of the device? (3 pts)
e) What is the peak magnitude of the current that flows through the device? (3 pts)
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ENGR-4300
Test 4B
Fall 2006
Question 3 – Mixed Signals (17 points)
In the circuit below LEDs D1 and D2 are used to activate phototransistors Q1 and Q2
respectively. Assume that when activated, the phototransistors may be treated as ideal
switches that are closed with zero resistance between the emitter and collector.
+5V
1
2
U1
LED 1
100
~
~
D1
+8V
Q1
V1
1k
R9
U3
8k
+
OUT
-
+5V
100
LED 2
~
~
D2
1
2
+8V
Vout
OPAMP
Q2
V2
R10
4k
U2
a) If the top switch U1 is closed, what is the voltage at V1? (4 pts)
b) If the bottom switch U2 is closed, what is the voltage at V2? (4 pts)
c) If the switches are such that Q1 is on (closed) and Q2 is off (opened),with the op amp
configured as a weighted adder, what is the value of Vout? (4 pts)
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ENGR-4300
Test 4B
Fall 2006
d) If the switches are such that Q1 is off (opened) and Q2 is on (closed),with the op amp
configured as a weighted adder, what is the value of Vout? (4 pts)
e) If the circuit below is added so that the 2k resistor is connected to the op amp’s ‘-‘ input,
will toggling switch U3 have any affect on Vout? (Answer carefully.) (3 pts)
+5V 1
2
U3
LED3
D3
100
~
~
+8V
Q3
V3
R11
2k
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ENGR-4300
Test 4B
Fall 2006
Short problems (48 points)
Answer 8 of the following 9, each is worth 6 pts.
Indicate which problem shouldn’t be graded or we will grade the first 8, including
blanks.
4) For the circuit below:
R1
1k
V1
A
15V
R2
1k
R3
1k
0
A) What is the voltage at point A? (include units)
B) What is the current through R2? (include units)
5) For the circuit below:
R
L
1
2
Vout
Vin
C
0
A) What is the transfer function (Vout(jω)/Vin(jω))? Write it as a ratio of polynomials.
B) What is the low frequency approximation?
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ENGR-4300
Test 4B
Fall 2006
6) For the circuit below:
100uH
1
Vin
2
500 ohms
Vout
A) What type of filter is this circuit?
B) What is the corner frequency in Hertz?
7) For the diagram below:
v(t)
6
4
voltage
2
0
-2
-4
-6
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
time (sec)
The waveform pictured is of the form: v(t )  Ae t cos(t  )
What are A, α, and ω? Include units.
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0.004
0.0045
0.005
ENGR-4300
Test 4B
Fall 2006
8) For the transformer circuit below:
N1:N2
Vin
Rload
Given: N1:N2 is equal to 1:10 and Rload=500Ω
A) If Vin is 5sin(ωt)V, what is the voltage across the resistor, Rload?
B) For part A, what is the current through Rload?
C) For part A, what is the current out of the source, Vin?
9) For the circuit below:
A
8V
2k
1k
2k
B
Draw the Thevenin equivalent circuit as seen from points A and B. Label the component
values, including units.
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ENGR-4300
Test 4B
Fall 2006
10) Use the circuit below.
U3 7
3
+
0
R3
OUT
2
2k
V1 = .2
V2 = -.2
TD = .05m
TR = 0.1u
TF = .1u
PW = .1m
PER = .2m
-
4
uA741
0
9V
V+
5
OS2
OS1
V-
6
Vout2
1
Vin1
0
-9V
C3
0
2nF
The upper plot below is a trace of Vin1 for the circuit above. Draw Vout on the lower plot.
Label the y axis for the lower plot. Assume that Vout is 0V at t=0.
400mV
0V
-400mV
Vin
0
0s
100us
200us
Plot Vout2
300us
400us
Time
11) Use the circuit below:
R5
Vout
500 ohms
D6
D1N4148
Vin
D7
D1N4148
D9
D1N4148
D10
D1N4148
A) All diodes have an on voltage of 0.7V,
otherwise are ideal. Vin is scanned from -5V to
+5V. What are the maximum and minimum
voltages at Vout?
D11
D1N4148
D12
D1N4148
0
B) Using the values in part A, what is the
maximum magnitude of the current through the
resistor?
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ENGR-4300
Test 4B
Fall 2006
12) For the logic circuit shown:
U1A
1
A
3
2
U4A
1
7400
B
3
2
U3A
1
2
Y
7408
U1B
7404
4
6
C
5
7400
Complete the table:
C
0
0
0
0
1
1
1
1
B
0
0
1
1
0
0
1
1
A
0
1
0
1
0
1
0
1
Y
Remember: Do 8 of the last 9 problems. Mark which one shouldn’t be
graded, or we will grade the first 8.
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