Name ______________
Partner______________
Date ______________
Laboratory
3
Diode & Rectifier
Preparation
/ Reading:
Text: 6.8 (or reference [1]: 5.9)
Lecture notes
Questions marked (*) in this lab script.
OBJECTIVE
LC Resonant circuit; Half-wave rectifier; Full-wave Bridge Rectifier;
Ripple; Rectified differentiator; Diode Clamp; Diode Limiter .
EQUIPMENT REQUIRED
Oscilloscope (Tektronix TDS210, dual channel, 60 MHz)
Function generator (BK Precision 4011A, sine, triangle, square, logic
level; to 5 MHz)
Breadboard (PB-503, powered, with a built-in function generator)
Digital multimeter (DMM, FLUKE 187)
Variac (transformer)
12.6 V transformer
560 pF capacitor (1)
0.01 uF capacitor (1)
15 uF capacitor (1)
10 mH inductor (1)
1N914 Si diode (5)
1 k resistor (1)
2.2 k resistor (2)
100 k resistor (1)
270 Ω resistor (1)
1N4734A Zener Diode -5.5V (1)
2N5785 or 2N3053 Transistor
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Lab 3-1: LC Resonant Circuit --- To study LC circuit and to use it to detect Fourier
components of a square wave
* 1. Consider the parallel resonant circuit shown below. Calculate the resonant frequency f0 at
which Vout/Vin reaches the maximum, give your derivations.
Fig. 3.1
f0 (calculated) = _______
2. Determine the resonant frequency experimentally.
Drive above circuit with a sine wave, varying the frequency through a range around the
resonant frequency. Measure the resonant frequency, and compare with the one you calculated
above. (The circuit attenuates the signal considerably, even at its resonance frequency.)
3. Verify the amplitudes and frequencies of the first 3 terms of the Fourier series of a square
wave.
This resonant circuit (Fig. 3.1) can serve as a “Fourier Analyzer”: The resonant frequency
of the circuit is fixed at approximately f0=16 kHz (ie. the circuit is a 16 kHz-detector). If the input
signal has a component sine wave which matches this frequency, a resonance will be observed
at the circuit output.
(Here is a reminder of the Fourier series for a square wave:
A square wave of frequency ‘f’ will have component sine waves at higher frequencies of
3f, 5f, 7f, etc. Drive the circuit with a square wave at the circuit resonant frequency f 0 and note
the amplitude of the sine wave response at the circuit output. Now gradually lower the driving
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frequency ‘f’ until you observe another resonance (this occurs when the second Fourier
component at frequency 3f matches the circuit resonant frequency f 0). Record the driving
frequency and amplitude of the output sine wave when this occurs. Repeat this measurement for
the third Fourier component.
Measurements:
Square wave frequency (kHz) | Output amplitude: Vp (
)
------------------------------------------- |---------------------------------------|
|
|
|
|
|
|
4. Discuss your results above. Are the measured frequencies and amplitudes what you expect?
* 5. Now drive the circuit with a sine wave at the resonant frequency f 0 of the circuit and measure
the amplitude of the output. Can you estimate the value of pi () based on this amplitude, and
those measured above?


Lab 3-2: Half-wave Rectifier
1. Construct a half-wave rectifier circuit, as shown below (Fig.3.2). Set the function generator to a
1 kHz sine wave with 8 Vp-p with the scope.
Fig. 3.2
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* 2. Sketch the input and output of the circuit below (ensure that the scope is set to DC coupling).
What is the peak output voltage value measured? Is it what you expect?
(Remember to number the horizontal and vertical gridlines, or indicate their respective scales .)
Lab 3-3: Full-wave Bridge Rectifier
1.
Construct a full-wave bridge circuit as shown in Fig. 3.3 (a). Before connecting the
transformer to your circuit, adjust the Variac until the transformer output is 6.3Vrms (use the DMM,
set to AC, to measure this voltage). Then turn off the power before connecting other
components.
Be sure that the diodes are inserted correctly and that grounding is as shown (Otherwise
you may burn out diodes, and in this circuit diodes usually fail in pairs! ). Fig. 3.3 (b) gives you
practical hints on the connections.
(a)
(b)
Fig. 3.3
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2. Use the scope (DC coupling) to observe the output waveform. Record the waveform, and label
the max and min values.
Warning: Don’t attempt to look at the input 6.3Vac with the scope’s other channel at the
same time; this would require connecting the second “ground” lead of the scope to one
side of the secondary, that may cause a disaster.
3. What is the peak amplitude? Is it what you expect?
* 4. Look at the region of the output waveform that is near zero volts. Why are there flat regions?
Measure their duration, and explain.
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* 5. Ripple --- Connect a 15 uF filter capacitor across the output (be careful about the polarity).
Does the output make sense? Measure the amplitude of the peak-to-peak “ripple”. Is it what you
expect?
Lab 3-4 Rectified differentiator
1. Construct a circuit shown in Fig. 3.4. Drive it with a square wave at 10 kHz or so, at the
function generator’s maximum output amplitude. Look at input and output, using both scope
channels.
Sketch the output waveform you observe, does it make sense?
Fig. 3.4
2. What does the 2.2 k load resistor do? Try to remove it (to make the load infinite). Can you see
the difference in output waveform? Explain. (Hint: compare the RC discharge curves.)
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Lab 3-5 Diode Clamp
1. Construct the simple diode clamp circuit shown in Fig. 3.5. Drive it with a large amplitude sine
wave from your function generator, and observe the output of the circuit.
Sketch the waveform, and label the maximum and minimum. Discuss the results.
Fig. 3.5
* 2. Try using a voltage divider as the clamping voltage, as shown in Fig.3.6 (ignore the capacitor
drawn in dotted lines for now). Drive the circuit with a large sine wave, and examine the peak of
the output waveform. Why is it rounded so much? (Hint: what happens to the reference voltage
when a current flows through the diode? You may draw a Thevenin model for the voltage divider
if that helps.)
Fig. 3.6
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* 3. As a remedy, try adding a 15 uF capacitor, as shown with dotted lines (note polarity) in
Fig.3.6. Record your observations and explain why it works. This case illustrates well the concept
of a bypass capacitor (or decoupling capacitor).
Lab 3-6 Diode Limiter
Build the simple diode limiter shown in Fig.3.7. Drive it with sine, triangle, and square waves of
various amplitudes. Describe what it does based on your observation, and explain why. Can you
think of a use for it?
Fig.3.7
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