EECS 318
Electronics Lab
Laboratory #9
Diode Circuits
Objective:
The purpose of this laboratory is to demonstrate the function of diodes. Diodes will be
used to alter waveforms. Clipping and clamping circuits will be constructed.
Equipment:
1 - Analog Probe Kit
1 - Breadboard
1 - DC Power Supply
1 - Function Generator
1 - Oscilloscope
Components:
1 - 1kΩ Resistor
2 - IN4001 Diode
2 - 300 Ω Resistor
1 - 0.15 µF Capacitor
Procedure:
1. Construct the circuit shown below on a breadboard.
1 kΩ
+
Vs
+1 0 V
t
-1 0 V
Vs
V
+
-
wire
jumper
(function
generator)
6 .5 V
o
wire
jumper
6 .5 V
-
Circuit Schematic #1 - Clipping Circuit 1
2. For this circuit, set the function generator to a 1kHz triangle output, with a peakto-peak voltage of 20V, and attach the red (positive) terminal to the resistor and
the black (negative) terminal to “ground” (the bottom node). On the DC power
supply, set the +/–20V power supplies to +/-6.5 volts. Attach the +/–20V
terminals to their respective nodes on the breadboard. Attach the black, common
terminal on the DC power supply to “ground” (the bottom node). Also, use
jumper wires to attach the diodes to the power sources. (Later, these jumper wires
will be replaced by resistors.)
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3. Measure the input and output voltage waveforms simultaneously on the
oscilloscope by using different channels on the oscilloscope. For this
measurement, attach the ground clips of the oscilloscope to “ground” (the bottom
node) and the probe to the + nodes associated with the input and output voltages.
Sketch the input and output waveforms. Press Default setup to erase any previous
settings. Make sure the coupling mode is set to DC, probe ratios set to 10:1 and
BW limit is set to ON.
Q1: How do the input and output waveforms differ? Why do they differ?
(Assume the diodes are ideal.)
4. Assuming that the diodes behave ideally, use circuit analysis to predict the
theoretical output voltage waveform for the given input waveform.
Q2: How does the theoretical output waveform compare to the measured
output waveform?
5. Next, replace the wire jumpers in the circuit with 300Ω resistors to obtain the
circuit shown below. Keep the oscilloscope probes attached, and do not change
the function generator settings.
1kΩ
+
Vs
(function
generator)
+V
s
-
+
300 Ω
-
6 .5 V
6.5 V
Circuit Schematic #2 - Clipping Circuit 2
2
Vo
300Ω
-
6. Measure the input and output voltage waveforms simultaneously on the
oscilloscope. Sketch the input and output waveforms.
Q3: How have these resistors altered the output waveform? What kind of
familiar waveform is the output waveform?
7. Construct the circuit shown below on a breadboard. Set the function generator for
a 20 V peak to peak square wave at a frequency of 1 KHz.
C = .15 µF
Vs
+
+1 0 V
t
-1 0 V
V
s
+
-
Vo
(function
generator)
-
Circuit Schematic #3 - Clamping Circuit
8. Measure the input and output voltage waveforms simultaneously on the
oscilloscope. Sketch the input and output waveforms, taking care to note the 0 V
levels on each waveform.
Q4: How do the input and output waveforms differ?
9. The key to understanding how this circuit works is to apply Kirchhoff’s Voltage
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Law (KVL). The output voltage is the sum of the source voltage and the
capacitor voltage. When the function generator starts, the diode allows current to
flow in the counterclockwise direction, but not clockwise. Over several cycles of
the input square wave, the capacitor voltage builds up to equal the negative peak
value of the signal source.
10. There are load resistance limitations to be considered when using clamping
circuits in practice. Place a 10kΩ resistor in parallel using the decade resistance
box with the output terminals and sketch the output. Repeat this for a 1kΩ resistor.
Remember that the diode is essentially “off” (an open-circuit) when the source
voltage is +10, during which the capacitor discharges through the load resistor.
The diode is “on” (i.e., nearly a short circuit) when the source voltage is -10 V,
during which the capacitor charges through the very small resistance of the diode.
Q5: Explain the effects of the load resistance in terms of the
charge/discharge time constant (τ = RC) of a series resistor/capacitor
circuit.
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