Download AB22 Class B Amplifier (Push-Pull Emitter Follower) Analog Lab

AB22
Class B Amplifier
(Push-Pull Emitter Follower)
Analog Lab
Experiment Board
Ver. 1.0
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An ISO 9001: 2000 company
AB22
94-101, Electronic Complex, Pardesipura INDORE-452010, India.
Tel.: 91-731-2570301 Fax: 91-731-2555643
Email: [email protected] Web: www.scientech.bz
Scientech Technologies Pvt. Ltd.
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AB22
Scientech Technologies Pvt. Ltd.
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AB22
Class B Amplifier
Push-Pull Emitter Follower
AB22
Table of Contents
1.Introduction
3
2. Theory
5
3.Experiment
To study the operation of Class B Amplifier.
(Push-Pull Emitter Follower)
11
4.Datasheet
13
5.Warranty
15
6.List of Service Centers
16
7.List of Accessories
17
8. Notes
18
Scientech Technologies Pvt. Ltd.
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Introduction
AB22 is a compact, ready to use Class B Amplifier (Push-Pull Emitter
Follower) experiment board. This is useful for students to understand the
working and operation of various power amplifier categories. It can be used
as stand alone unit with external DC power supply or can be used with
SCIENTECH Analog Lab ST2612 which has built in DC power supply,
AC power supply, function generator, modulation generator, continuity
tester, toggle switches, and potentiometer.
List of Boards :
Model
Name
AB01
AB02
AB03
AB04
AB05
AB06
AB07
AB08
AB09
AB10
AB11
AB12
AB13
AB14
AB15
AB16
AB17
AB18
AB19
AB20
AB21
AB23
AB25
Diode characteristics (Si, Zener, LED)
Transistor characteristics (CB NPN)
Transistor characteristics (CB PNP)
Transistor characteristics (CE NPN)
Transistor characteristics (CE PNP)
Transistor characteristics (CC NPN)
Transistor characteristics (CC PNP)
FET characteristics
Rectifier Circuits
Wheatstone Bridge
Maxwell’s Bridge
De Sauty’s Bridge
Schering Bridge
Darlington Pair
Common Emitter Amplifier
Common Collector Amplifier
Common Base Amplifier
Cascode Amplifier
RC-Coupled Amplifier
Direct Coupled Amplifier
Class A Amplifier
Class C Tuned Amplifier
Phase Locked Loop (FM Demodulator & Frequency
Divider / Multiplier)
Multivibrator (Mono stable / Astable)
F-V and V-F Converter
V-I and I-V Converter
Zener Voltage Regulator
Transistor Series Voltage Regulator
AB28
AB29
AB30
AB31
AB32
Scientech Technologies Pvt. Ltd.
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AB22
AB33
AB35
AB39
AB41
AB42
AB43
AB44
AB45
AB49
AB51
AB52
AB54
AB56
AB57
AB58
AB59
AB64
AB65
AB66
AB67
AB68
AB80
AB82
AB83
AB84
AB85
AB88
AB89
AB90
AB91
AB92
AB93
AB96
AB97
AB101
AB102
AB106
Transistor Shunt Voltage Regulator
DC Ammeter
Instrumentation Amplifier
Differential Amplifier (Transistorized)
Operational Amplifier (Inverting / Non-inverting /
Differentiator)
Operational Amplifier (Adder/Scalar)
Operational Amplifier (Integrator/ Differentiator)
Schmitt Trigger and Comparator
K Derived Filter
Active filters (Low Pass and High Pass)
Active Band Pass Filter
Tschebyscheff Filter
Fiber Optic Analog Link
Owen’s Bridge
Anderson’s Bridge
Maxwell’s Inductance Bridge
RC – Coupled Amplifier with Feedback
Phase Shift Oscillator
Wien Bridge Oscillators
Colpitt Oscillator
Hartley Oscillator
RLC Series and RLC Parallel Resonance
Thevenin’s and Maximum power Transfer Theorem
Reciprocity and Superposition Theorem
Tellegen’s Theorem
Norton’s theorem
Diode Clipper
Diode Clampers
Two port network parameter
Optical Transducer (Photovoltaic cell)
Optical Transducer (Photoconductive cell/LDR)
Optical Transducer (Phototransistor)
Temperature Transducer (RTD & IC335)
Temperature Transducer (Thermocouple)
DSB Modulator and Demodulator
SSB Modulator and Demodulator
FM Modulator and Demodulator
………… and many more
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Theory
The power amplifiers are the amplifiers which deliver maximum
undistorted symmetrical output voltage swing to the low impedance load.
Generally any system (like a stereo, radio or television) consists of several
stages of amplification. When the signal passes through these stages, the
power level of signal rises so much that the later stages require high power
handling circuit elements such as power transistors. Also as the load
impedance of these later stages is very small (of the order of 8 ohm for
stereo amplifier speakers), heavy collector current flows. To handle this,
transistors heaving power rating of 1W or more are used in power
amplifiers.
Power amplifiers are broadly classified as :
1.
Class A (Voltage Amplifier)
2.
Class B (Push-Pull Emitter Follower)
3.
Class C
Class B Amplifier :
Class B amplifier is a circuit in which transistor conducts (collector current
flows) for only 180° of input AC signal. When a signal is applied, one half
cycle will forward bias the base-emitter junction and IC will flow. The other
half cycle will reverse bias the base-emitter junction and IC will be cut off.
Fig. 1
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For class B amplifiers the Q point is located near the cutoff point of the AC
load line. Thus, to amplify entire input AC signal a combination of two
Class - B amplifiers are used. One of which amplifies positive half cycle of
input AC signal and the other amplifies negative half cycle of input AC
signal. This amplifier configuration is known as push-pull or
complementary symmetry. In the push-pull configuration it is important to
match the two transistors carefully for the proper amplification of both the
halves.
While the input signal being amplified through class B amplifier the input
signal has to rise to about 0.7V to overcome the barrier potential of
amplifying transistor. During this period no current flows through the
circuit and output is zero. The action is similar for both the transistors.
Thus, following characteristic is obtained for input and output voltages:
Fig. 2
The output signal no longer remains sine wave and gets distorted. Since the
clipping occurs between the time one transistor cuts off and the time the
other one comes on we call it crossover distortion.
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Input and output waveforms illustrating the deed-zone/crossover distortion
Fig. 3
To remove the crossover distortion a slight forward bias is applied to each
emitter diode i.e. we locate the Q point of both the transistors slightly above
the cutoff. Thus collector current in both the transistors flows for more than
180° but less than 360°. Sometimes we call such an amplifier as Class AB
amplifier.
Fig. 4
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Operating parameters of Class B Amplifier :
Voltage Gain :
It is the ratio of output voltage (Vout) obtained to input voltage (Vin).
Av = Vout / Vin
Fig. 5
Input Impedance :
It is the ratio of Input voltage (Vin) to Input Current (Ii).
Zin = Vin / Ii
To measure the input impedance a known resistor (Rs) is placed in series
before the input coupling capacitor and the impedance could be calculated
using the equation.
Zin = RS / [AV / (AV'-I)]
Where,
AV = voltage gain without the resistor (RS)
AV' = voltage gain with the resistor (RS)
Output Impedance :
It is the ratio of Output voltage (Vout) to Output Current (IO).
Zout = Vout / Io
To measure the output impedance a known resistor (RS) is placed from
output to ground and the output impedance could be calculated using the
equation.
Zout = [AV / (AV'-I)] * RS
Where,
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AV = voltage gain without the resistor (RS)
AV' = voltage gain with the resistor (RS)
Current gain :
It is the ratio of output current (Io) to Input current (Ii).
Ai = Io / Ii
The Current gain could be calculated using the equation
Ai = -AV * Zin / RL
Power Gain :
It is the ratio of output AC power (Po) to input AC power (Pi).
PO = Vo(P-P)2 / (8 * RL) = Vrms2 / RL
Pi = Vin (p-p)2 / (8 * Zin) = Vin(rms)2 / Zin
The Power Gain can be calculated using the equation
Ap = Po / Pi
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Experiment
Objective :
To study the operation of Class B Amplifier.
Apparatus required :
1.
Analog board of AB22
2.
Variable DC power supplies +5V and -5V from external source or
ST2612 Analog Lab
3.
Function Generator
4.
Oscilloscope.
Circuit diagram :
Circuit used to show the Class B Amplifier operation is as shown below :
Fig. 6
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Procedure :
•
•
Connect +5V and -5V DC power supplies at their indicated position
from external source or ST2612 Analog Lab.
Connect 2Vp-p AC signal (1 KHz) at the Vin input of the AB22.
1.
Put the pot P1 to its minimum position i.e. rotate it fully
anticlockwise. (This is the condition when no bias voltage is applied
to the emitter diodes of both the transistors.)
2.
Connect Oscilloscope at the output terminals of AB22 and observe
the output waveform. The crossover distortion can be clearly
observed on the oscilloscope.
3.
Gradually increase the bias voltage by increasing bias resistance (i.e.
rotate the pot in clockwise direction) up to the value when the
crossover distortion is completely removed and maximum
amplification of the input signal is obtained.
4.
Connect the input AC signal to the Class B amplifier through 100
ohms series resistance.
5.
Measure the input and output voltage amplitude and also input and
output impedance as describe earlier.
6.
Measure the power gain of class B amplifier using the operating
parameters as described in class B theory.
Results :
Input AC voltage amplitude (Vin) : ...........................Vp-p
Input Impedance (Zin) : ..........................................Ohms
Input Current (Ii) : ........................................................A
Output AC voltage amplitude (Vout) : .......................Vp-p
Output impedance (RL) : .........................................ohms
Output current (Io) : ......................................................A
Power gain (Ap) : .............................................................
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Datasheet
Scientech Technologies Pvt. Ltd.
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Scientech Technologies Pvt. Ltd.
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Warranty
1) We guarantee the instrument against all manufacturing defects during
24 months from the date of sale by us or through our dealers.
2) The guarantee covers manufacturing defects in respect of indigenous
components and material limited to the warranty extended to us by the
original manufacturer, and defect will be rectified as far as lies within
our control.
3) The guarantee will become INVALID.
a) If the instrument is not operated as per instruction given in the
instruction manual.
b) If the agreed payment terms and other conditions of sale are not
followed.
c) If the customer resells the instrument to another party.
d) Provided no attempt have been made to service and modify the
instrument.
4) The non-working of the instrument is to be communicated to us
immediately giving full details of the complaints and defects noticed
specifically mentioning the type and sr. no. of the instrument, date of
purchase etc.
5) The repair work will be carried out, provided the instrument is
dispatched securely packed and insured with the railways. To and fro
charges will be to the account of the customer.
DESPATCH PROCEDURE FOR SERVICE
Should it become necessary to send back the instrument to factory please
observe the following procedure:
1) Before dispatching the instrument please write to us giving full details
of the fault noticed.
2) After receipt of your letter our repairs dept. will advise you whether it
is necessary to send the instrument back to us for repairs or the
adjustment is possible in your premises.
Dispatch the instrument (only on the receipt of our advice) securely packed
in original packing duly insured and freight paid along with accessories and
a copy of the details noticed to us at our factory address.
Scientech Technologies Pvt. Ltd.
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List of Service Centers
1. Scientech Technologies Pvt. Ltd.
90, Electronic Complex
Pardesipura,
INDORE – 452010
2. Scientech Technologies Pvt. Ltd.
First Floor, C-19,
F.I.E., Patparganj Industrial Area,
DELHI – 110092
3. Scientech Technologies Pvt. Ltd.
1st floor No 1 Karpagam Gardens
Main Road Adyar
CHENNAI – 600020
4. Scientech Technologies Pvt. Ltd.
202/19, 4th main street
Ganganagar,
BANGALORE- 560032
5. Scientech Technologies Pvt. Ltd.
8,1st floor, 123-Hariram Mansion,
Dada Saheb Phalke road,
Dadar (East),
MUMBAI –400014
6. Scientech Technologies Pvt. Ltd.
988, Sadashiv Peth,
Gyan Prabodhini Lane,
PUNE – 411030
7. Scientech Technologies Pvt. Ltd
SPS Apartment, 1st Floor
2, Ahmed Mamoji Street,
Behind Jaiswal Hospital,
Liluah, HOWRAH-711204 W.B.
8. Scientech Technologies Pvt. Ltd
Flat No. 205, 2nd Floor,
Lakshminarayana Apartments
‘C’ wing, Street No. 17,
Himaytnagar,
HYDERABAD- 500029
Scientech Technologies Pvt. Ltd.
Ph : (0731) 2570301
Email : [email protected]
Ph : (011) 22157370, 22157371
Fax : (011) 22157369
Email : [email protected]
Ph : (044) 42187548, 42187549
Fax : (044) 42187549
Email : [email protected]
Ph : (080) 51285011
Fax : (080) 51285022
Email : [email protected]
Ph : (022) 56299457
Fax : (022) 24168767
Email : [email protected]
Ph : (020) 24461673
Fax : (020) 24482403
Email : [email protected]
Ph : +913355266800
Email : [email protected]
Ph : (040) 55465643
Email : [email protected]
17
AB22
List of Accessories
1.
2mm Patch cord (red) .........................................................1 Nos.
2.
2mm Patch cord (black) ......................................................3 Nos.
3.
2mm Patch cord (blue) ........................................................3 Nos.
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Notes
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Notes
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Notes
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