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Download AB22 Class B Amplifier (Push-Pull Emitter Follower) Analog Lab
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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. 2 AB22 Scientech Technologies Pvt. Ltd. 3 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. 4 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 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. 5 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 Scientech Technologies Pvt. Ltd. 6 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 Scientech Technologies Pvt. Ltd. 7 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. Scientech Technologies Pvt. Ltd. 8 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 Scientech Technologies Pvt. Ltd. 9 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. 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, Scientech Technologies Pvt. Ltd. 10 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) = 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 Scientech Technologies Pvt. Ltd. 11 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 Scientech Technologies Pvt. Ltd. 12 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) : ............................................................. Scientech Technologies Pvt. Ltd. 13 AB22 Datasheet Scientech Technologies Pvt. Ltd. 14 AB22 Scientech Technologies Pvt. Ltd. 15 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. Scientech Technologies Pvt. Ltd. 16 AB22 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. Scientech Technologies Pvt. Ltd. 18 AB22 Notes Scientech Technologies Pvt. Ltd. 19 AB22 Notes Scientech Technologies Pvt. Ltd. 20 AB22 Notes Scientech Technologies Pvt. Ltd. 21