Bangladesh University of Engineering and Technology
Department of Electrical and Electronic Engineering
Dhaka-1205, Bangladesh
EEE 106 : Electrical Circuits-II Laboratory (Hardware)
Experiment Number - 4
Name of the Experiment:
Frequency Response of Passive Circuit Elements L and C, and
A Practical LC low pass Filter
Prepared By:
Ramit Dutta, Asikur Rahman Jowel, Dr. Orchi Hassan & Dr. Md. Ziaur Rahman Khan,
Dept of EEE, BUET on June 2022
Evaluation Form:
IMPORTANT! You must complete this experiment during your scheduled lab period. All
work for this experiment must be demonstrated to and verified by your lab instructor before
the end of your scheduled lab period. This lab will not be graded
STEP
DESCRIPTION
MAX
1
Prelab Task
5
2
Frequency Response of L and C
10
3
Low Pass LC Filter Characteristic
10
TOTAL
25
SCORE
Signature of Evaluator:
Academic Honesty Statement:
IMPORTANT! Please carefully read and sign the Academic Honesty Statement, below. You
will not receive credit for this lab experiment unless this statement is signed in the presence of
your lab instructor.
“In signing this statement, I hereby certify that the work on this experiment is my own andthat I have not copied
the work of any other student (past or present) while completing this experiment. I understand that if I fail to honor
this agreement, I will receive a score of ZEROfor this experiment and be subject to possible disciplinary action.”
Name:
E-mail:
Lab Group:
Date:
@eee.buet.ac.bd Signature:
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Contents
Evaluation Form: .......................................................................................................................... 2
Academic Honesty Statement: ..................................................................................................... 2
Prelab Exercise: ............................................................................................................................ 4
Objective ........................................................................................................................................ 5
Frequency Response of L and C .................................................................................................. 5
Low Pass LC Filter Characteristic:............................................................................................. 9
Figures
Figure 1: A Passive Crossove Circuit ........................................................................................................ 5
Figure 2: Frequency Response of L and C ............................................................................................... 6
Figure 3: Circuit for Unfiltered Output .................................................................................................... 9
Figure 4: Circuit for Filtered Output ...................................................................................................... 10
Tables
Table 1: Data for Crossover Frequency .................................................................................................... 7
Table 2 : Output voltage V1 across R1...................................................................................................... 7
Table 3 : Output voltage V2 across R2...................................................................................................... 8
Table 4: Low Pass LC Filter Characteristic ........................................................................................... 10
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Prelab Exercise:
(1) Find out the resonant frequency of the circuit shown above.
(2) Show that the circuit is a low pass filter.
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Objective
The frequency response of a simple two-way L and C passive crossover is investigated. One
output should attenuate signals above the crossover frequency while the other output should
attenuate signals below the crossover frequency.
Frequency Response of L and C
Overview:
Figure 1: A Passive Crossover Circuit
A crossover circuit is one which splits the frequency that passes through it. It is designed to meet
the operating range of frequency of speaker. As inductors and capacitors exhibit a reactance that
is a function of frequency, they are ideal candidates for passive crossovers. In this experiment, a
simple two-way crossover is examined. It has one output for the high frequency transducer (i.e.,
tweeter) and for the low frequency transducer (i.e., woofer) as shown in Fig 1. When you put a
capacitor in series with a speaker, the lower frequencies are filtered. When you put an inductor in
series with a speaker, the higher frequencies are filtered. In place of the transducers, two resistive
loads are used. This has the added advantage of not producing any sound in the laboratory. While
real-world crossovers tend to be more complex than the one in this exercise, it will suffice to
show the basic operation.
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Figure 2: Frequency Response of L and C
Procedure:
1. The circuit of Figure 2 can be thought of as a pair of frequency dependent voltage dividers.
XL increases with frequency, thus attenuating high frequency signals reaching R2.
Similarly, XC increases with a decrease in frequency, thus attenuating low frequency
signals reaching R1.
2. The crossover frequency is the frequency where R1 = XC and R2 = XL (normally the same
frequency for both. Using C=260nF, L=2.6mH, and R1 = R2 = 100Ω, determine the
crossover frequencies and record in Table 1.
3. Using the voltage divider rule and Ein = 2 V p-p, determine and record the theoretical
voltage at output one (V1) for each frequency listed in Table 2. Be sure to include both
magnitude and phase.
4. Now, build the circuit of Figure 1 using R1 = R2 = 100Ω, L=2.6mH, and C = 260nF. Place
one probe of the oscilloscope across the generator and another across output one (R1). Set
the generator to a 2 V p-p sine wave at 100 Hz.
5. Measure and magnitude and phase shift of the output with respect to the input and record
in Table 2. Repeat the measurements for the remaining frequencies in the Table 2.
6. Repeat Steps 3 through 5 for the second output (V2) and record in Table 3.
7. On a single graph plot the magnitude response of both outputs with respect to frequency.
On a separate graph plot the phase response of both outputs with respect to frequency.
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Table 1: Data for Crossover Frequency
Components
Crossover Frequency
Using R1 = XC
R1 = R2 = 100Ω
C=260nF
L=2.6mH
Show Calculation
Using R2 = XL
Show Calculation
Table 2 : Output voltage V1 across R1
Frequency
(Hz)
100
|V1| (V)
(Theoretical)
∠V1 (Deg)
(Theoretical)
|V1| (V)
(Experimental)
∠V1 (Deg)
(Experimental)
200
500
1k
2k
5k
10k
20k
25k
30k
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Table 3 : Output voltage V2 across R2
Frequency
(Hz)
100
|V2| (V)
(Theoretical)
∠V2 (Deg)
(Theoretical)
|V2| (V)
(Experimental)
∠V2 (Deg)
(Experimental)
200
500
1k
2k
5k
10k
20k
25k
30k
Questions for report:
1. Find cross over frequency from your plots and compare it with theoretical ones.
2. Do the plots resemble like filters? If yes, comment on types and validate it theoretical calculation
also.
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Overview:
This part of the experiment shows the application of passive LC low pass filter to obtain dc output
from a pulsating rectified output (dc or zero frequency + may high frequency multiple of supply
50 Hz. supply frequency).
Procedure:
1. Construct the following circuit (Fig 3) with the
components provided in the laboratory. You will be
using the following diode as shown on the right.
Connect the function generator (12Vp-p and 50
Hz) across A & B.
1
2
Full-Wave Rectifier
Oscilloscope channel 1
A
S
B
S
100
0
230/12
2. Here, the input AC signal will be rectified by a diode bridge. The output of the bridge
rectifier without filtering a pulsating dc consists of dc+ac (of many frequencies of 100 and
above Hz.) Draw (or Record) the waveform observed with the oscilloscope in Table 4.
3. Now, Construct the circuit shown in Fig 4. The value of the inductor is 2.6mH. The filtered
dc output (rectified pulsating dc) may be observed at the output resistance with a low pass
LC filter between rectifier and the load. Draw (or Record) the waveform observed with the
oscilloscope in Table 4.
Transformer
1-ph 50 Hz AC
230VAC
Low Pass LC Filter Characteristic:
Oscilloscope Reference
Figure 3: Circuit for Unfiltered Output
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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Full-Wave Rectifier
Oscilloscope channel 1
C
+
-
100
B
S
2
220u
A
S
1
L
2
230/12
1
Transformer
1-ph 50 Hz AC
230VAC
0
Oscilloscope Reference
Figure 4: Circuit for Filtered Output
Table 4: Low Pass LC Filter Characteristic
Waveform of Unfiltered Output
Waveform of Filtered Output
Note: In power applications, passive filters are used composed of L and C only to avoid loss in R.
However, in low power (signal processing) applications RC filters with active elements like OP
Amps can be used where resistances of high values are used practically drawing no current and
hence causing insignificant loss.
Questions For Report:
1. Draw a conclusion from filtered and unfiltered outputs.
2. Calculate cut off frequency of the filter theoretically.
3. Comment on phase response of the filter.
EEE 106 – Electrical Circuits-II Laboratory (Hardware)– Experiment 3
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