Download Experiment - University of Guelph Physics

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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 that with the one you
calculated. (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
at the f0.
This resonant circuit (Fig. 3.1) can serve as a “Fourier Analyzer”: the detector-frequency
is fixed (approximately 16 kHz, say, the circuit is a 16 kHz-detector), you can change the
frequency of an input square wave to measure one or another sine wave component of the
square wave.
(Here is a reminder of the Fourier series for a square wave:
Drive the circuit with a square wave at f0, note the amplitude of the sine wave response. Now gradually lower
the driving frequency until you get another peak response --a smaller bump at f0/3, and check the amplitude -should be 1/3 the amplitude of the fundamental response. And so on.)
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Measurements:
Square wave frequency (kHz) | Output amplitude: Vp (
)
------------------------------------------- |---------------------------------------|
|
|
|
|
|
|
4. Discuss your results above, are they what you expect?
* 5. Can you determine pi value () based on your data?




Lab 3-2: Half-wave Rectifier
1. Construct a half-wave rectifier circuit, as shown below (Fig.3.2). Record the measured value of
the resistance. 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. Observe the output on the scope with DC coupling setting. (You may preset the 0 V line at
the middle of the scope’s screen, using the GND position of the coupling switch of the scope.) Is it
what you expect? What is the peak output voltage value measured?
Sketch the waveform above, label the max and min values of the waveform. (Remember to
record the chosen vertical and horizontal sensitivity on the scope.)
Lab 3-3: Full-wave Bridge Rectifier
1.
Construct a full-wave bridge circuit as shown in Fig. 3.3 (a). First of all, adjust the Variac
in connection with the 12.6 V transformer to make the end output = 6.3 V rms, use DMM (set to AC)
to monitor the end output (of the 12.6 V transformer) during the adjustment. Then turn off the
power to connect 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 of the waveform.
(NOTE: 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?
6. Regulator (optional) --- --- We don’t expect you to understand how the components work yet ( we’ll
learn transistors later); we just want you to meet them experimentally.
The regulator circuit is as shown below: it uses a Zener diode as a voltage reference (VZ = 5.5V),
and a single transistor connected as a voltage follower (or Emitter Follower). Double check to be
sure you have not accidentally interchanged any of the transistor leads, also the connections on
the Zener diode. Connect the input of this circuit to the capacitor above, check the output
waveform after the regulator, any “ripple” now?
Write down what you observed.
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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? Why? (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 sine wave from your
function generator, at very large output amplitude, and observe the output of the circuit. (If you
can see that the clamped voltage is not quite flat, then you see the effect of the diode’s non-zero
impedance.)
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. Drive the circuit with
a large sine wave, and examine the peak of the output waveform. Why is it rounded so much?
(Hint: what is the impedance of the “voltage source” provided by the voltage divider? You may
draw a Thevenin model for the circuit)
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. Explain to your satisfaction 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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