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

QUALITY POLICY

To be a Global Leader of Innovative, Competitive and

Eco friendly Electronic Equipment, Software Products and Turn-key Solutions for Industry and Technology

Training. We will achieve this by enhancing Costumer

Satisfaction based on Research, Modern manufacturing techniques and continuous improvement in Quality of the products and the Services. The key drivers to growth will be focus on Employees and Customers, Use of latest

Technology, Intense Marketing, Service Support and High

Ethical Practices.

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

Class B Amplifier

Push-Pull Emitter Follower

AB22

Table of Contents

1.Introduction

2.

Theory

3.

Experiment

To study the operation of Class B Amplifier.

(Push-Pull Emitter Follower)

4.

Datasheet

5.

Warranty

6.

List of Service Centers

7.

List of Accessories

8. Notes

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17

18

11

13

15

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5


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AB13

AB14

AB15

AB16

AB17

AB18

AB19

AB20

AB21

AB23

AB25

AB01

AB02

AB03

AB04

AB05

AB06

AB07

AB08

AB09

AB10

AB11

AB12

AB28

AB29

AB30

AB31

AB32

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

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


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AB33

AB35

AB39

AB41

AB42

AB59

AB64

AB65

AB66

AB67

AB68

AB80

AB82

AB83

AB84

AB85

AB88

AB89

AB90

AB91

AB43

AB44

AB45

AB49

AB51

AB52

AB54

AB56

AB57

AB58

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 I

C

will flow. The other half cycle will reverse bias the base-emitter junction and I

C

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 (V out

) obtained to input voltage (V in

).

Av = V out

/ V in

Fig. 5

Input Impedance :

It is the ratio of Input voltage (V in

) to Input Current (I i

).

Z in

= V in

/ I i

To measure the input impedance a known resistor (R s

) is placed in series before the input coupling capacitor and the impedance could be calculated using the equation.

Where,

A

V

= voltage gain without the resistor (R

S

A

V'

= voltage gain with the resistor (R

S

)

)

Output Impedance :

Z in

= R

S

/ [A

V

/ (A

V'

-I)]

It is the ratio of Output voltage (V out

) to Output Current (I

O

).

Z out

= V out

/ I o

To measure the output impedance a known resistor (R

S

) is placed from output to ground and the output impedance could be calculated using the equation.

Z out

= [A

V

/ (A

V'

-I)] * R

S

Where,


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A

V

= voltage gain without the resistor (R

S

)

A

V'

= voltage gain with the resistor (R

S

)

Current gain :

It is the ratio of output current (I o

) to Input current (I i

).

A i

= I o

/ I i

The Current gain could be calculated using the equation

A i

= -A

V

* Z in

/ R

L

Power Gain :

It is the ratio of output AC power (P o

) to input AC power (P i

).

P

O

= V o(P-P)

2 / (8 * R

L

) = V rms

2 / R

L

P i

= V in (p-p)

2 / (8 * Z in

) = V in(rms)

2 / Z in

The Power Gain can be calculated using the equation

A p

= P o

/ P i


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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 2V p-p

AC signal (1 KHz) at the V in

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 (V in

) : ...........................V

p-p

Input Impedance (Z in

) : ..........................................Ohms

Input Current (I i

) : ........................................................A

Output AC voltage amplitude (V out

) : .......................V

p-p

Output impedance (R

L

) : .........................................ohms

Output current (I o

) : ......................................................A

Power gain (A p

) : .............................................................


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Datasheet


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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.


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List of Service Centers

1. Scientech Technologies Pvt. Ltd.

90, Electronic Complex

Pardesipura,

INDORE – 452010


First Floor, C-19,

F.I.E., Patparganj Industrial Area,

DELHI – 110092


1 st floor No 1 Karpagam Gardens

Main Road Adyar

CHENNAI – 600020


202/19, 4 th main street

Ganganagar,

BANGALORE- 560032


8,1st floor, 123-Hariram Mansion,

Dada Saheb Phalke road,

Dadar (East),

MUMBAI –400014


988, Sadashiv Peth,

Gyan Prabodhini Lane,

PUNE – 411030

7. Scientech Technologies Pvt. Ltd

SPS Apartment, 1 st Floor

2, Ahmed Mamoji Street,

Behind Jaiswal Hospital,

Liluah, HOWRAH-711204 W.B.

8. Scientech Technologies Pvt. Ltd

Flat No. 205, 2 nd Floor,

Lakshminarayana Apartments

‘C’ wing, Street No. 17,

Himaytnagar,

HYDERABAD- 500029

Ph : (0731) 2570301

Email : [email protected]

Ph : (011) 22157370, 22157371

Fax : (011) 22157369


Ph : (044) 42187548, 42187549

Fax : (044) 42187549


Ph : (080) 51285011

Fax : (080) 51285022


Ph : (022) 56299457

Fax : (022) 24168767


Ph : (020) 24461673

Fax : (020) 24482403


Ph : +913355266800


Ph : (040) 55465643



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

•

•

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