Class B Push Pull

AB22Class B Amplifier

(Push-Pull Emitter Follower)

Analog LabExperiment Board

Ver. 1.0

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AB22

94-101, Electronic Complex, Pardesipura INDORE-452010, India.Tel.: 91-731-2570301 Fax: 91-731-2555643Email: [email protected] Web: www.scientech.bz

Scientech Technologies Pvt. Ltd. 2

http://www.scientech.bz/

mailto:[email protected]

AB22


AB22

Class B AmplifierPush-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


AB22

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 Diode characteristics (Si, Zener, LED)AB02 Transistor characteristics (CB NPN)AB03 Transistor characteristics (CB PNP)AB04 Transistor characteristics (CE NPN)AB05 Transistor characteristics (CE PNP)AB06 Transistor characteristics (CC NPN)AB07 Transistor characteristics (CC PNP)AB08 FET characteristicsAB09 Rectifier CircuitsAB10 Wheatstone Bridge AB11 Maxwell’s BridgeAB12 De Sauty’s BridgeAB13 Schering BridgeAB14 Darlington PairAB15 Common Emitter AmplifierAB16 Common Collector AmplifierAB17 Common Base AmplifierAB18 Cascode AmplifierAB19 RC-Coupled AmplifierAB20 Direct Coupled AmplifierAB21 Class A AmplifierAB23 Class C Tuned AmplifierAB25 Phase Locked Loop (FM Demodulator & Frequency

Divider / Multiplier)AB28 Multivibrator (Mono stable / Astable)AB29 F-V and V-F ConverterAB30 V-I and I-V ConverterAB31 Zener Voltage Regulator AB32 Transistor Series Voltage Regulator


AB22

AB33 Transistor Shunt Voltage RegulatorAB35 DC AmmeterAB39 Instrumentation AmplifierAB41 Differential Amplifier (Transistorized)AB42 Operational Amplifier (Inverting / Non-inverting /

Differentiator)AB43 Operational Amplifier (Adder/Scalar)AB44 Operational Amplifier (Integrator/ Differentiator)AB45 Schmitt Trigger and ComparatorAB49 K Derived FilterAB51 Active filters (Low Pass and High Pass)AB52 Active Band Pass Filter AB54 Tschebyscheff Filter AB56 Fiber Optic Analog LinkAB57 Owen’s BridgeAB58 Anderson’s BridgeAB59 Maxwell’s Inductance BridgeAB64 RC – Coupled Amplifier with FeedbackAB65 Phase Shift OscillatorAB66 Wien Bridge OscillatorsAB67 Colpitt OscillatorAB68 Hartley OscillatorAB80 RLC Series and RLC Parallel Resonance AB82 Thevenin’s and Maximum power Transfer TheoremAB83 Reciprocity and Superposition TheoremAB84 Tellegen’s TheoremAB85 Norton’s theoremAB88 Diode ClipperAB89 Diode ClampersAB90 Two port network parameterAB91 Optical Transducer (Photovoltaic cell)AB92 Optical Transducer (Photoconductive cell/LDR)AB93 Optical Transducer (Phototransistor)AB96 Temperature Transducer (RTD & IC335)AB97 Temperature Transducer (Thermocouple)AB101 DSB Modulator and DemodulatorAB102 SSB Modulator and DemodulatorAB106 FM Modulator and Demodulator

………… and many more


AB22

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


AB22

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.


AB22

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


AB22

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. 5Input 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,


AB22

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) = Vrms

2 / RL

Pi = Vin (p-p)2 / (8 * Zin) = Vin(rms)

2 / Zin

The Power Gain can be calculated using the equation

Ap = Po / Pi


AB22

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


AB22

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


AB22

Datasheet


AB22


AB22

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.


AB22

List of Service Centers

1. Scientech Technologies Pvt. Ltd.90, Electronic Complex Ph : (0731) 2570301Pardesipura, Email : [email protected] INDORE – 452010

2. Scientech Technologies Pvt. Ltd.First Floor, C-19, Ph : (011) 22157370, 22157371F.I.E., Patparganj Industrial Area, Fax : (011) 22157369DELHI – 110092 Email : [email protected]

3. Scientech Technologies Pvt. Ltd.1st floor No 1 Karpagam Gardens Ph : (044) 42187548, 42187549Main Road Adyar Fax : (044) 42187549CHENNAI – 600020 Email : [email protected]

4. Scientech Technologies Pvt. Ltd.202/19, 4th main street Ph : (080) 51285011Ganganagar, Fax : (080) 51285022BANGALORE- 560032 Email : [email protected]

5. Scientech Technologies Pvt. Ltd.8,1st floor, 123-Hariram Mansion, Ph : (022) 56299457Dada Saheb Phalke road, Fax : (022) 24168767Dadar (East), Email : [email protected] –400014

6. Scientech Technologies Pvt. Ltd.988, Sadashiv Peth, Ph : (020) 24461673Gyan Prabodhini Lane, Fax : (020) 24482403PUNE – 411030 Email : [email protected]

7. Scientech Technologies Pvt. LtdSPS Apartment, 1st Floor Ph : +9133552668002, Ahmed Mamoji Street, Email : [email protected] Jaiswal Hospital, Liluah, HOWRAH-711204 W.B.

8. Scientech Technologies Pvt. LtdFlat No. 205, 2nd Floor, Ph : (040) 55465643Lakshminarayana Apartments Email : [email protected]‘C’ wing, Street No. 17,Himaytnagar, HYDERABAD- 500029


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.


AB22

Notes


AB22

Notes


AB22

Notes


Documents

Class B Push Pull