EE2201 E2002
LAB 2 - Diode Applications PRELAB
P1. For the diode circuit of Fig. P2-1, the zener diode has a reverse breakdown voltage of 5V.
Find the output voltage v
OUT
and currents i
Z
, i
R1
, and i
L
.
P2. Calculate the power dissipated in each component, and determine if there are any components exceeding their maximum power rating. (Assume for the purposes of this problem that the resistors have a maximum power rating of 1/4 watt; and that the zener diode is rated for a maximum power of 1/2 watt)
R1
33

+ i
R1 i
L
+10 i
Z
D1
+
V
OUT
-
R L
220

Figure P2-1.
For the diode circuit of Fig. P2-2, v
IN
is a 60Hz sine wave with an rms amplitude of 10V.
(Remember that, for a sine wave, the peak amplitude is a factor of 2 larger than the rms amplitude!).
P3. Plot (as a function of time) v
OUT
and v
IN
for a few cycles of the input sine wave.
P4. Determine the average DC value of the output voltage v
OUT
, and the frequency and peak-topeak amplitude of the ripple waveform “riding” on the output DC voltage.
D2
1N4004
+ v
IN
-
C F
100µF
+
R L
1k

+
V
OUT
-
Fig. P2-2.
1

EE2201 E2002 - LAB 2
Diode Applications:
Regulated DC Power Supply
Signal Processing Circuits
PURPOSE:
The purpose of this laboratory assignment is to investigate two types of diode application circuits: power (regulated DC supply, using the 1N4004 and 1N751A) and signal processing
(waveshaping and level shifting circuits using the 1N4148. Upon completion of this lab you should be able to:
 Recognize the reverse breakdown region of operation in the zener diode.
 Recognize different types of transformer and rectifier circuit configurations (half-wave, fullwave)
 Measure performance of the diode rectifier with a filter capacitor to produce an unregulated
DC voltage
 Use a zener diode to reduce the “ripple” of the unregulated voltage, producing a smooth DC voltage
 Recognize and characterize diode signal processing circuits such as the clamped capacitor
(DC restore) and “voltage doubler.”
MATERIALS:
 ECE Lab Kit
 DC Power Supply
 DVM
 Function Generator
 Oscilloscope
 Transformer box
NOTE: Be sure to record ALL results in your laboratory notebook.
Transformer terminal designation reminder: Yellow posts indicate “dotted” transformer pins:
Be sure to switch off power when making wiring changes!
2

120
VAC
YL W
BLK
YL W
BLK
3

ZENER DIODE: V-I CHARACTERISTIC
V-I Characteristic: Reverse breakdown region
L1. Build the diode circuit shown in Fig. 2-1, using the 1N751 (or equivalent 1N5231B) zener diode for D1. Note that the power supply is configured to apply a reverse bias voltage to the zener diode; also, the DVM is configured to measure the voltage drop across the 100Ω resistor R1. i
D
D1 i
L
-
V
D
+
V SUPPL
+ i
R1
R1
100

+
V
R1
-
+
DV
-
Figure 2-1.
L2. Sweep the power supply from 0V to 10V (use increments of 1V), and record the voltage drop across R1. Calculate the voltage on the reverse biased diode from v
D
= v
R1
– v
SUPPLY
(1)
Also calculate the current that flows in each case, from i
D

 v
R 1
R
1
Note that Eq. (2) assumes i
L
is negligible, so that i
D
≈-i
R
.
(2)
L3. Plot the V-I characteristic. Note the “constant-voltage-drop” behavior for a sufficiently negative voltage/current! This is the reverse breakdown region.
Constant-voltage-drop model
L4. If you were modeling this zener diode with a constant-voltage-drop model for the reverse breakdown region, what voltage would you use to model operation for reverse currents near
20mA?
4

HALF WAVE RECTIFIER
L5. The goal of this application is to convert a 120Vrms, AC signal from the wall outlet to a smooth 5V DC power supply voltage. The transformer’s job is to step down the 120Vrms
AC signal to a lower voltage signal – but since transformers can only pass AC, we need to do something with the low voltage AC signal to make DC.
Half wave rectifier (no filter capacitor)
L6. Using the transformer box, build the half wave rectifier circuit shown in Fig 2-2, using the
1N4004 for diode D2. We will only need one of the transformer’s two secondary windings for this part of the lab.
The 1kΩ resistor R
L
simulates the electrical load that would be powered by this power supply
Input, output waveforms
L7. Set up the oscilloscope to view the rectifier input (transformer output) v
IN
on channel 1 at
5V/div, and v
OUT
on channel 2 at 5V/div. Set both inputs to zero (GND) and adjust the vertical position of each trace so that both are centered vertically. Once the vertical position is adjusted correctly, when viewing the voltage waveforms, be sure both channels are on DC coupling.
Set up the time base of the scope to show at least one full cycle of the sine wave.
L8. Sketch the input and output waveforms as shown on the oscilloscope, and measure the frequency of the sine wave coming out of the transformer.
How well does this circuit meet the functional goal expressed in section L5?
D2
1N4004
YLW
BLK
YLW
+
V
IN
-
R
1k
L

+
V
OUT
-
120
VA
BLK
Figure 2-2.
5

Half wave rectifier (with filter capacitor)
L9. Modify the half wave rectifier circuit by adding a 100µF filter capacitor, as shown in Fig 2-
3.
NOTE: BE SURE TO OBSERVE THE CORRECT ORIENTATION OF THE
POLARIZED CAPACITOR!
Depending on the manufacturer, there will be an indication for the positive or negative terminal. Be sure that the + terminal is connected to the more positive voltage! If the capacitor is backward, excessive current can flow and permanent damage can occur.
Input, output waveforms
L10. Sketch the input and output waveforms as shown on the oscilloscope.
Compared to the circuit without the filter capacitor, how well does this circuit meet the functional goal expressed in section L5?
Note any change in shape of the waveform (especially at the peak) compared to the case of the circuit without the filter capacitor in section L8. What might cause the change in shape?
Ripple waveform
L11. Using the AC coupling feature on the oscilloscope, measure the frequency and peak-to-peak amplitude of the ripple waveform “riding” on the output DC voltage. How does this compare with your prediction from prelab P4?
D2
1N4004
YLW
BLK
YLW
+
V
IN
-
C F
100µF
+
R L
1k

+
V
OUT
-
120
VA
BLK
Figure 2-3.
6

FULL WAVE RECTIFIER
Consider the half-wave rectifier with filter capacitor of Figure 2-3. One interpretation of the ripple waveform is that the capacitor receives charge through the rectifier diode only once per cycle of the 60Hz sine wave, and then only for a short period of time. When the rectifier diode is off, the capacitor is “on its own”, and is discharged by the load current. As the load current discharges the capacitor, the output voltage decays, reaching a minimum value just before the rectifier diode turns on at the next cycle. This causes the “ripple” waveform you observe on the oscilloscope.
To create a smooth DC voltage, we’d like to reduce the ripple to as small a value as possible.
One strategy is to increase the value of the filter capacitor. However, this usually is accompanied by increase in size and cost.
Another possibility is to reduce the amount of time the capacitor is “on its own” before the diode turns on again. Then the output voltage will have less time to decay, reducing the ripple. We can’t increase the frequency of the 60Hz line voltage coming out of the wall. But we can take advantage of the other transformer winding to make another 60Hz sine wave, 180° out of phase, that will help:
L12. Remove the filter capacitor, and build the full wave rectifier shown in Fig. 2-4.
YLW
V
IN1
D2
1N4004
BLK
YLW
R L
1k
 V
+
-
OUT
120
VA
BLK
V
IN2
D3
1N4004
Figure 2-4.
Center-tapped transformer waveforms
L13. Set up the oscilloscope to view v
IN1
on channel 1 at 5V/div, and v
IN2
on channel 2 at 5V/div.
Set both inputs to zero (GND) and adjust the vertical position of each trace so that both are centered vertically. Once the vertical position is adjusted correctly, when viewing the voltage waveforms, be sure both channels are on DC coupling.
Set up the time base of the scope to show at least one full cycle of the sine wave.
L14. Sketch the v
IN1
and v
IN2
waveforms. Verify that they are 180° out of phase.
7

Full wave rectifier (without filter capacitor)
L15. Use channel 2 on the oscilloscope to observe v
OUT
. Sketch the v
OUT
waveform. How does it compare with the output from the unfiltered half wave rectifier in part L8?
Full wave rectifier (with filter capacitor)
L16. Modify the full wave rectifier circuit by adding a 100µF filter capacitor, as shown in Fig 2-
5. BE SURE TO OBSERVE THE CORRECT ORIENTATION OF THE POLARIZED
CAPACITOR!
Input, output waveforms
L17. Sketch the output waveform as shown on the oscilloscope. Compared to the circuit without the filter capacitor in section L15, how well does this circuit meet the functional goal expressed in section L5?
Ripple waveform
L18. Using the AC coupling feature on the oscilloscope, measure the frequency and peak-to-peak amplitude of the ripple waveform “riding” on the output DC voltage. How does this compare with your measured result from section L11 for the half wave rectifier?
L19. Increase the total C
F
to 200µF by adding another 100µF capacitor in parallel with C
F
. (Be sure to observe correct polarity!). How is the ripple amplitude affected?
D2
1N4004
YLW
V
IN1
BLK
YLW
C F
100µF
+
R
1k
L

+
V
OUT
-
120
VA
BLK
V
IN2
D3
1N4004
Figure 2-5
8

FULL WAVE RECTIFIER WITH ZENER DIODE REGULATOR
In the previous part of the lab, you saw how ripple can be reduced by using both phases of the
60Hz sine wave, and by increasing the size of the filter capacitor. To achieve even lower ripple
(and a better approximation to the ideal of a constant DC voltage), we'll use a zener diode.
Full wave rectifier (with filter capacitor and zener regulator)
L20. Modify the full wave rectifier circuit by adding the zener diode regulator subcircuit, as shown in Fig. 2-6. Be careful with the wiring! The 100µF filter capacitor should connect to the 1N4004 diodes; the zener should be in parallel with the load resistor R
L
.
Input, output waveforms
L21. Sketch the input and output waveforms as shown on the oscilloscope. ALSO, sketch the capacitor waveform v
C
.
Compared to the previous two circuits, how well does this circuit meet the functional goal expressed in section L5?
Ripple waveform
L22. Using the AC coupling feature on the oscilloscope, measure the frequency and peak-to-peak amplitude of the ripple waveform “riding” on the output DC voltage. How does this compare with your measured value from section L18, without the zener regulator?
YLW
V
IN1
D2
1N4004
R 2
100

R L
1k

BLK
YLW
+
+
V
C
-

D4
1N751
+
V
OUT
-
120
VA
BLK
V
IN2
C F
1
00µF
D3
1N4004
Figure 2-6.
9

CLAMPED CAPACITOR (DC RESTORE) CIRCUIT
Application
L23. When a signal must pass through many stages of transmission and amplification, significant
DC errors can accumulate from each stage; in some applications (e.g. video broadcast) DC information cannot even be transmitted directly since the signal is modulated onto a high frequency carrier. If the most negative voltage of the signal corresponds to a known DC level, then the correct DC value can be “restored” by using the clamped capacitor circuit.
L24. Build the clamped capacitor circuit (also referred to as a “DC restore” circuit) shown in
Figure 2-7. Using the function generator, set up v
IN
to be a 10kHz square wave with 10V peak-to-peak amplitude. Set up the oscilloscope to view v
IN
on channel 1 at 5V/div, and v
OUT
on channel 2 at 5V/div. Set both channels to DC coupling. Using the vertical position knobs on the scope, adjust the GND reference level so that v
IN
is shown on the top half of the scope display, and v
OUT
is on the bottom half.
Input, output waveforms
L25. The function of this circuit is to “clamp” the most negative voltage of the input signal to be
0.7V (one diode drop) below ground – regardless of the DC component of v
IN
. Observe this behavior by varying the DC offset of the input square wave v
IN
over a range of several volts
(be sure to pull out the OFFSET knob on the function generator to change the offset). You should see the DC offset level of the output remain unchanged.
C4
0.1µF
+ v
I
-
D4
1N4148
R L
100k

+
V
OUT
-
Figure 2-7.
10

VOLTAGE DOUBLER
Application
L26. In battery powered circuitry, the supply voltage is (seemingly) limited to the voltage provided by the battery. If a higher voltage is required, one obvious solution is to simply connect more batteries in series. Adding batteries, however, increases cost, size, and weight, which we’d rather not do – especially since in some portable applications (e.g. pager, cell phone) the battery is the dominant factor in determining size and weight. In these portable applications, adding an extra battery would impose a significant size and weight penalty.
The voltage doubler offers another way to develop voltages larger than the battery voltage, requiring only capacitors and diodes. The circuit in Fig 2-8 is one of many variations that provide the performance advantages of the voltage multiplying concept.
L27. Modify the clamp circuit of Fig 2-7 by adding a rectifier circuit composed of diode D5 and capacitor C5 as shown in Figure 2-8. Also, add 10kΩ resistor R
L
to simulate circuitry drawing current from v
OUT
.
L28. Using the function generator, set up v
IN
to be a 10kHz square wave with 10V peak-to-peak amplitude and zero offset (push in the OFFSET know on the function generator). Set up the oscilloscope to view v
IN
on channel 1 at 5V/div, and v
OUT
on channel 2 at 5V/div. Set both channels to DC coupling. Using the vertical position knobs on the scope, adjust the GND reference level so that v
IN
and v
OUT
both have their GND levels at the middle of the scope display.
C4
0.1µF
D5
1N4148
V
4 v
IN
+
-
D4
1N4148
C 5
0.01µF
R L
100k

+
V
OUT
-
Figure 2-8.
Input, output waveforms
L29. The function of this circuit is to provide a DC output voltage that is approximately twice the peak voltage of the input. Observe this behavior by measuring the output voltage v
OUT
on the oscilloscope. You should see a DC voltage approximately twice the peak of the input square wave.
11

Deviations from ideal: Ripple
L30. Just like the rectifier circuits in the previous sections of this lab, the D5-C5 rectifier will exhibit some ripple on the output. Using AC coupling, “zoom in” on the output waveform and measure the peak-to-peak ripple on the output.
Deviations from ideal: DC value
L31. Is the DC value exactly twice the peak of the input? If not, by how much does it differ from the ideal (twice the peak) value? Explain why there is a difference (qualitative), and why it is the value you observe (quantitative).
12

LAB WRITEUP
1N751 ZENER DIODE: V-I CHARACTERISTIC
W1. Using your measured data, plot the overall V-I characteristic on linear axes. Identify the forward bias, reverse bias, and reverse breakdown operating regions.
W2. On the same axes with your data plot from section W1, plot the V-I characteristic of the constant-voltage-drop reverse breakdown model you determined in section L4.
W3. Discussion: Compare your measured data to the constant-voltage-drop model. How well does the constant-voltage-drop model predict the diode’s V-I behavior? Are there any deviations from the model (e.g. at low currents or high currents)?
HALF WAVE RECTIFIER
W4. Plot the input and output waveforms. Indicate any important information (for example, peak voltage values, frequency, etc.) on your plot.
W5. Discussion: How well does this circuit meet the functional goal expressed in section L5?
Half wave rectifier (with filter capacitor)
W6. Plot the input and output waveforms. Indicate any important information (for example, peak-to-peak ripple amplitude, average output voltage value, etc.) on your plot.
W7. Discussion: Compared to the circuit without the filter capacitor, how well does this circuit meet the functional goal expressed in section L5?
W8. Discussion: How did the measured ripple value compare with your prediction from prelab
P4? Try to explain any discrepancy.
13

FULL WAVE RECTIFIER
Full wave rectifier (without filter capacitor)
W9. Plot the output waveform. How does it compare with the output from the unfiltered half wave rectifier in part L8?
Full wave rectifier (with filter capacitor)
W10. Plot the output waveform as shown on the oscilloscope.
W11. Discussion: Compared to the circuit without the filter capacitor, how well does this circuit meet the functional goal expressed in section L5?
Ripple waveform
W12. Plot the frequency and peak-to-peak amplitude of the ripple waveform “riding” on the output DC voltage.
W13. How does this ripple compare with your measured value from sections W6-W8, for the half wave rectifier? Explain (qualitatively and quantitatively!) any differences.
Full wave rectifier (with filter capacitor and zener regulator)
W14. Plot the input and output waveforms and the capacitor waveform v
C
.
W15. Discussion: Compared to the previous two circuits, how well does this circuit meet the functional goal expressed in section L5?
Ripple waveform
W16. Plot the frequency and peak-to-peak amplitude of the ripple waveform “riding” on the output DC voltage. How does this compare with your measured value from section L18, without the zener regulator?
14

CLAMPED CAPACITOR (DC RESTORE) CIRCUIT
Input, output waveforms
W17. Plot the output of this circuit for a few different values of DC offset on the input signal.
W18. Discussion: Explain how this circuit “clamps” the most negative voltage of the input signal to be 0.7V (one diode drop) below ground – regardless of the DC component of v
IN
.
VOLTAGE DOUBLER
Input, output waveforms
W19. Plot the input and output voltages of this circuit.
Deviations from ideal: Ripple
W20. Plot the ripple waveform on the output, including the frequency and peak-to-peak amplitude.
W21. Discussion: Explain the ripple, both qualitatively and quantitatively: derive an equation to provide a theoretical prediction of the measured ripple. How does your measured value compare to the theoretical?
Deviations from ideal: DC value
W22. Is the DC value exactly twice the peak of the input? If not, by how much does it differ from the ideal (twice the peak) value? Explain why there is a difference (qualitative), and why it is the value you observe (quantitative).
15