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Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3

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UNIVERSITI MALAYSIA PERLIS

ANALOGUE ELECTRONIC IEMT 249/112

EXPERIMENT # 3

CLASS A POWER AMPLIFIER

MARKS

Pre LabCalculation

DC + ACOperation

Power AmplifierMeasurement

Discussion ConclusionTotalMarks

100%

8 9 7 3 3 30

NAME PROGRAMME

MATRIK # DATE

8/10/2019 EXP3-Class a Power Amplifier - 2013_14

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EXPERIMENT 3CLASS A POWER AMPLIFIER

1. OBJECTIVE

1.1 To observe the effect of the quiescent operating point (Q point) and the input signal level on

the output signal distortion.1.2 To determine the DC input power.1.3 To determine the AC input power.1.4 To determine the amplifier power gain.1.5 To determine the amplifier efficiency.1.6 To determine the transistor power loss.

2. EQUIPMENTS & COMPONENTS

2.1 Oscilloscope2.2 Function generator

2.3 Voltmeter2.4 Breadboard2.5 Resistors: 10k, 4.7k, 1.0k (3), 560 (1), 10 (2)2.6 Capacitors: 2.2F (2), 47F (1)2.7 Transistor 2N3904

3. INTRODUCTION

Power amplifiers are used to deliver a large amount of power to a load. Typically, voltage amplifiers arecascaded together to amplify the input signal and the power amplifier will be the last stage ofamplification.

The class of an amplifier refers to the design of the circuitry within the amplifier. There are manyclasses used for audio amps; Class A, B, AB, C, D and other classes such as G, H, S, etc.

Class A power amplifiers are amplifiers that are biased in the active region. Under normal operation,the transistor will never saturate or cut off. Class A power amplifiers are often used for signal levelcircuit because they maintain low distortion. Distortion for class A power amplifiers increases as thesignal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit.

The ratio load power delivered to power drawn from the dc supply is called the efficiency, _ of anamplifier. In many cases, it is more important to have the highest efficiency possible to deliver the mostpower to the load. The efficiency, can be calculated using the following equations:

average power delivered to load / average power drawn from dc source

where:

PS = VCC IQ

PL

IQ is the quiescent collector current

VL(peak) is the peak value of a sinusoidal load voltage

VL(p-p) is the peak topeak value of a sinusoidal load voltage

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4. PROCEDURE:

TABLE 1

4.1 DC Operation

i) From Figure 1, do a pre-lab calculation for:

Assume DC = 100 VBE(on) = 0.7 V

a) VBBb) RBc) REd) RCe) IBf) ICg) IEh) VCEQ

ii) Connect the amplifier circuit.

iii) Measure and record the values of VCC, VCEQ and ICQ.

iv) Based from the measured values, sketch a DC load line (IC vs VCE). Indicate the major points.

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Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3

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4.2 AC Operation

i) Indicate the major points, superimpose the AC load line and the DC load line in the same graph.

ii) From the previous calculated values, calculatea) RL based on AC load line slopeb) Find the new value of RloadV (RloadV here is not 1k anymore)

4.3 Power Amplifier Measurements (AC & DC Operation)

i) Set the function generator output to 0.2V peak-to-peak at 1 kHz.

ii) Set both oscilloscope channels to ac coupled.

iii) Trigger source can be set to channel 1 which is then used as the input reference.

iv) Set gnd positions on both channels.

v) Set a new value of R loadV

vi) Decrease the input voltage until the channel 2 oscilloscope shows maximum undistorted outputvoltage. The power amplifier operates at maximum undistorted output voltage.

vii) Measure new values (after decreasing the input voltage):a) Vinb) Iinc) Voutd) Iout

viii) Calculate the values of (to calculate power, the values must be in rms)a) Pin,b) Poutc) AP

d) PIN(DC) ; Where VIN(DC)~VCC and IIN(DC)~ICQe) Efficiency

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5. DISCUSSION

i) Define class A operation in terms of transistor conduction.

ii) State class A performance in terms of efficiency & distortion.

iii) When is maximum output voltage obtained?

iv) What is the maximum possible overall class A efficiency?

v) When does transistor maximum power dissipation occur?

6. CONCLUSION

Make your overall conclusion by referring to the objective of this experiment (your answer should be insimple notes).