ab24 transformer coupled amplifier · ab24 transformer coupled amplifier ... in an analog amplifier...

AB24 Transformer Coupled Amplifier

Operating Manual Ver.1.1

An ISO 9001 : 2000 company

94-101, Electronic Complex Pardesipura, Indore- 452010, India Tel : 91-731- 2570301/02, 4211100 Fax: 91- 731- 2555643 e mail : [email protected] Website : www.scientech.bz Toll free : 1800-103-5050

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Scientech Technologies Pvt. Ltd. 2

AB24


Transformer Coupled Amplifier AB24

Table of Contents

1. Introduction 4

2. Theory 6

3. Experiments

a. Experiment 1 10 Study the frequency response of untuned Transformer coupled

Amplifier. b. Experiment 2 13 Study the frequency response of tuned Transformer coupled

Amplifier.

4. Data Sheet 16 5. Warranty 17

6. List of Accessories 17 7. Results 18

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Introduction AB24 is a compact, ready to use Transformer Coupled Amplifier experiment board. This board is useful for students to understand the working and operation of tuned and untuned Transformer coupled amplifier. 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 characteristics AB09 Rectifier Circuits AB10 Wheatstone bridge AB11 Maxwell’s Bridge AB12 De Sauty’s Bridge AB13 Schering Bridge AB14 Darlington Pair AB15 Common Emitter Amplifier AB16 Common Collector Amplifier AB17 Common Base Amplifier AB18 RC-Coupled Amplifier AB19 Cascode Amplifier AB20 Direct Coupled Amplifier AB21 Class A Amplifier AB22 Class B Amplifier (Push Pull Emitter Follower) AB23 Class C Tuned Amplifier AB25 Phase Locked Loop (FM Demodulator & Frequency Divider /

Multiplier) AB26 FET Amplifier AB27 Voltage Controlled Oscillator AB28 Multivibrator (Monostable / Astable) AB29 F-V and V-F Converter AB30 V-I and I-V Converter AB31 Zener Voltage Regulator AB32 Transistor Series Voltage Regulator AB33 Transistor Shunt Voltage Regulator AB35 DC Ammeter AB37 DC Ammeter (0-2mA) AB39 Instrumentation Amplifier

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AB41 Differential Amplifier (Transistorized) AB42 Operational Amplifier (Inverting / Non-inverting / Differentiator) AB43 Operational Amplifier (Adder/Scalar) AB44 Operational Amplifier (Integrator/ Differentiator) AB45 Schmitt Trigger and Comparator AB49 K Derived Filter AB51 Active filters (Low Pass and High Pass) AB52 Active Band Pass Filter AB54 Tschebyscheff Filter AB56 Fiber Optic Analog Link AB57 Owen’s Bridge AB58 Anderson’s Bridge AB59 Maxwell’s Inductance Bridge AB64 RC – Coupled Amplifier with Feedback AB66 Wien Bridge Oscillators AB67 Colpitt Oscillator AB68 Hartley Oscillator AB80 RLC Series and RLC Parallel Resonance AB82 Thevenin’s and Maximum Power Transfer Theorem AB83 Reciprocity and Superposition Theorem AB84 Tellegen’s Theorem AB85 Norton’s theorem AB88 Diode Clipper AB89 Diode Clampers AB90 Two port network parameter AB91 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 Demodulator AB102 SSB Modulator and Demodulator AB106 FM Modulator and Demodulator

and many more…………

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Theory Fundamentally an amplifier is a device that takes in a low power signal and outputs a magnified (power boosted) version of the input signal. In an analog amplifier using transistor,the signal is applied to the base terminal of the transistor and this causes a proportional output drive current to flow out of the output terminal. The output drive current is obtained from the power supply. The voltage signal at the output is thus a larger version of the input, but has been changed in sign (inverted) by the amplification. If the amplifying element is linear, then the output will be faithful copy of the input, only larger and inverted. In practice, transistors are not linear, and the output will only approximate the input.

Transformer coupled amplifier given here is a type of Class A amplifier. Class A amplifier,amplify over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. Class A amplifiers are the usual means of implementing small-signal amplifiers. In a Class A circuit, the amplifying element is biased such that the device is always conducting to some extent, and is operated over the most linear portion of its characteristic curve (known as its transfer characteristic curve).

Class A Amplifier

Figure 1 Some applications of a class A device is audio amplifier and almost all op-amps.

If the output of one amplifier is connected (coupled) to the input of another element, the element is said to be “coupled”. There are various methods of coupling which are

• Direct coupling

• RC coupling

• LC coupling

• Transformer coupling A Transformer Coupled Amplifier is a type of audio amplifier with an ideal frequency response from 15 Hz to 20 kHz. The frequency response of an amplifier can be shown graphically with a Frequency response curve. The frequency response curve shown in figure2 has two cutoffs at frequency f1 and f2. The cutoff at frequency f1 at 3 db down or at 70.7% of maximum value of voltage gain is called lower cutoff. The cutoff at f2 at 3 db down or at 70.7% of maximum value is called upper cutoff. The f1 and f2 points are known as half power points. Any frequency below f1 or above f2 point is not considered a usable output from the amplifier. The bandwidth of the amplifier is the difference between the f1 and f2 points .Frequency response shown in figure 2 is “ideally flat” from lower cutoff (f1) to upper cutoff (f2). Above upper cutoff or below

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lower cutoff the gain decreases or "drops off" quite rapidly. The Frequency response of an amplifier is determined by the components in the circuit.

The bandwidth of Transformer-Coupled Amplifier is given by, Bandwidth (B) = f2 – f1 =………KHz …. (1)

Figure 2

Transformer coupling is the most common method used to couple audio amplifiers. Transformer coupling has many advantages over RC coupling for audio amplifiers; for example, transformer coupling uses fewer components than capacitive coupling. It can also provide a means of increasing the gain of the stage by using a step-up transformer for voltage gain. If a current gain is required, a step-down transformer can be used.

The untuned Transformer coupled single-stage audio amplifier is shown in figure 3. This is a class A, common-emitter, audio amplifier. The output device (low impedance load) is shown connected to the secondary winding of the transformer. CC is a coupling capacitor which couples the input signal to the base of transistor Q1. Since the impedance of the capacitor is inversely proportional to frequency, the capacitor effectively blocks DC voltage and transmits ac voltage. When the frequency is high enough, the capacitive reactance is much smaller than the résistance. So capacitor used for this purpose is called a coupling capacitor.

In these circuit resistance R1 and R2 are used for voltage divider biasing to drive the transistor BC547. R2 develops the input signal. Re is used to bias the emitter of Q1 and provides temperature stability. R1 is used to bias the base of Q1. The primary of transformer (TR) is the collector load for Q1 and develops the output signal. Transformer couples the output signal to the low impedance load and provides impedance matching between the output impedance of the transistor (medium impedance) and the low impedance load.

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Figure 3

The advantages of transformer coupled amplifier are following : 1. There is complete DC isolation

2. It is relatively simple to match the amplifier and load impedance using a transformer.

3. A transformer-coupled circuit can easily be converted to a tuned amplifier; that is, a circuit that provides a specific value of gain over a specified range of operating frequencies.

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The figure 4 below shows the tuned Transformer coupled amplifier.

Figure 4

The disadvantages of transformer coupled amplifier are following.

• It is bulky due to presence of transformer.

• It is costly.

• At higher frequencies due to saturation of transformer core, output is nonlinear and distorted.

The practical limitation of transistor coupling is output distortion, if the output voltage surpasses the supply voltage; user will get a clipped output because at higher load resistances, amplifier gives high gain which clips off. Therefore input voltage is limited to certain value, so that output voltage does not clip off.

Another coupling method to couple the two stages is RC-coupling. RC Coupling has the advantages of wide frequency response and relatively small cost and size.

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Experiment 1 Objective : Study the frequency response of untuned transformer coupled amplifier Equipments Needed : 1. Analog board, AB24 2. DC power supply +12V,

3. Function Generator, 4. Oscilloscope,

5. 2mm patch cords.

Circuit diagram : Circuit used to study the operation of untuned Transformer-Coupled amplifier is shown below :

Figure 5

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Procedure : 1. Connect +12V variable DC power supply at the indicated position. 2. Switch ON the power supply. 3. Connect maximum 1.4 Vp-p, 1KHz sine wave signal at the signal input of

AB24 board and observe the same on oscilloscope CH I. 4. Connect socket ‘e’ with socket ‘g’ and socket ‘f’ with socket ‘h’. 5. Observe the output waveform between test point1 (TP1) and test point2 (TP2)

on oscilloscope CHI or CH II and note down output voltage (VOUT) peak to peak.

6. Vary the frequency of input signal from function generator with a margin of 1 KHz. After 10 to 12 readings the student can vary the frequency range with 10 KHz or 100 KHz margin.

7. Note down the output voltage corresponding the input frequency in the observation table given below.

8. Vary the input signal frequency up to 500 KHz. 9. Calculate the voltage gain of untuned transformer coupled amplifier at each

frequency by the formula given Voltage gain AV = VOUT (peak to peak) / VIN (peak to peak)

10. Find out the value of gain in db by formula Gain (in db) =20 log (AV)

11. Plot the graph between gain (in db) and frequency (in Hz) on log paper and calculate the bandwidth given by equation :

Bandwidth (B) = f2 – f1 =………KHz 12. Now connect socket ‘e’ with socket ‘i’ and socket ‘f’ with socket ‘h’. 13. Repeat steps from 5 to 11 for the connection in step 12.

14. The output waveform can be observed between test point1 and test point2 on oscilloscope CH I or CH II for the different values of input.

Note :The input voltage should be less than 1.4Vp-p, due to the reason that higher input voltage gives distortion in output.

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Observation Table : For input voltage VIN : ………

S. No.

Input signal

frequency (KHz)

Output voltage (VOUT )

Gain (AV=VOUT

/VIN )

Gain (db) 20 log (AV)

Note : Above input signal frequency of 100 KHz, output signal distorts.

Result : fL (lower 3dB cutoff frequency) = …………………… fH (higher 3dB cutoff frequency) = ……………………

Bandwidth (fH – fL ) = ……………………

Conclusion : The Bandwidth of untuned Transformer Coupled Amplifier is found to be ….. KHz.

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Experiment 2 Objective : Study of the frequency response of tuned transformer coupled amplifier Equipments Needed : 1. Analog board AB24. 2. DC power supply +12V from external source or ST2612 Analog Lab.

3. Function Generator. 4. Oscilloscope.

5. 2mm patch cords.

Circuit diagram : Circuit used to study the frequency response of transformer coupled amplifier is shown below :

Figure 6

Procedure : 1. Connect +12V variable DC power supply at the indicated position 2. Switch ‘On’ the power supply. 3. Connect maximum 1.4 Vp-p, 1KHz sine wave signal at the signal input of

amplifier of AB24 board and observe the same on oscilloscope CH I Once input voltage is set it should not be changed for the whole experiment.

4. Connect socket ‘a’ with socket ‘c’ and socket ‘b’ with socket‘d’. 5. Connect socket ‘e’ with socket ‘g’ and socket ‘f’ with socket ‘h’. 6. Observe the output waveform between test point1 (TP1) and test point2 (TP2)

on oscilloscope CH II and note down output voltage (VOUT) peak to peak.

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7. Vary the frequency of input signal from function generator with a margin of 1 KHz.

8. Note down the output voltage corresponding the input frequency in the observation table given below.

9. Vary the input signal frequency till the output voltage becomes equal to the input voltage.

10. Calculate the voltage gain of tuned transformer coupled amplifier at each frequency by the formula given Voltage gain AV= VOUT (peak to peak) / VIN (peak to peak)

11. Find out the value of gain in db by formula Gain (in db) =20 log (AV)

12. Plot the graph between gain (in db) and frequency (in Hz) on log paper and calculate the bandwidth given by equation : Bandwidth (B) = f2 – f1 =………KHz

13. Now connect socket ‘e’ and ‘i’, and socket ‘f’ and ‘h’. 14. Repeat steps from 5 to 12 for the connection in step 13. 15. The output waveform can be observed between test point 1 and test point 2 on

oscilloscope CH I or CH II for the different values of input. Note : The input voltage should be less than 1.4Vp-p, due to the reason that higher input voltage gives distortion in output.

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Observation Table : For input voltage : …….

S. No.

Input signal

frequency (KHz)

Output voltage (VOUT)

Gain (AV=VOUT

/VIN )

Gain (in db)

20 log (AV)

Result : Tuned Transformer Coupled Amplifier,

fL (lower 3dB cutoff frequency) = …………………… fH (higher 3dB cutoff frequency) = ……………………

Bandwidth (fH – fL) = …………………….

Conclusion : 1. The Bandwidth of tuned Transformer Coupled Amplifier is found to be ………

KHz. 2. Tuned Transformer Coupled Amplifier’s bandwidth is less than untuned

Transformer Coupled Amplifier.

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Data Sheet

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Warranty 1. We guarantee the product against all manufacturing defects for 24 months from

the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.

2. The guarantee will become void, if

a) The product is not operated as per the instruction given in the operating manual.

b) The agreed payment terms and other conditions of sale are not followed.

c) The customer resells the instrument to another party. d) Any attempt is made to service and modify the instrument.

3. The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.

4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.

For any Technical Problem Please Contact us at [email protected]

List of Accessories

1. 2mm Patch Cord (Red) 16”................................................................... 3 Nos.

2. 2mm Patch Cord (Blue) 16”.................................................................. 2 Nos.

3. 2mm Patch Cord (Black) 16” ............................................................... 3 Nos. 4. e-Manual ................................................................................................1 No.

Updated 26-06-2009

mailto:[email protected]

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Results Note : Teachers are requested to take out the result pages from manual and verify the results obtained by students.

Input Output

Case 1

Untuned Transformer

Coupled Amplifier with

load Resistance = 100

ohm.

Keep input signal voltage

maximum at = 1.4 Vpp

and input signal

frequency = 1KHz Vary

the Frequency with

margin of 1KHz

With variation in frequency

output increases initially then

becomes constant (with in

some limit) and then it

decreases.

Output at certain frequency

are :

At 1KHz = 1.6 volts

(sinusoidal)

At 20KHz = 2.2 volts

(sinusoidal)


(distorted)


(distorted)

Case 2

Untuned Transformer


load Resistance = 150

ohm.


maximum at = 1.4 Vpp

and input signal

frequency = 1KHz Vary



becomes constant (with in

some limit) and then it

decreases.


are :

At 1KHz = 2.1 volts

(sinusoidal)

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the Frequency with

margin of 1KHz


(sinusoidal)


(distorted)


(distorted)

Input Output

Case 3

Tuned Transformer


load Resistance = 100 ohm.


maximum at = 1.4 Vpp and

input signal frequency =

1KHz. Vary the Frequency

with margin of 1KHz

Output



becomes constant and then it

decreases.


are :

At 1KHz = 1.7 volts

(sinusoidal)

At 4KHz = 2.0 volts

(sinusoidal)

At 7KHz = 1.7 volts

(sinusoidal)


(sinusoidal)

Case 4

Tuned Transformer


Output



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load Resistance = 150 ohm.


maximum at = 1.4 Vpp and

input signal frequency =

1KHz Vary the Frequency

with margin of 1KHz

becomes constant and then it

decreases.


are :

At 1KHz = 2.2 volts

(sinusoidal)

At 4KHz = 2.8 volts

(sinusoidal)

At 7KHz = 2.2 volts

(sinusoidal)


(sinusoidal)

ab24 transformer coupled amplifier · ab24 transformer coupled amplifier ... in an analog amplifier...

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