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EXP3-Class a Power Amplifier - 2013_14

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   Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3 1   UNIVERSITI MALAYSIA PERLIS ANALOGUE ELECTRONIC I EMT 249/112 EXPERIMENT # 3 CLASS A POWER AMPLIFIER MARKS Pre Lab Calculation DC + AC Operation Power Amplifier Measurement Discussion Conclusion Total Marks 100% 8 9 7 3 3 30 NAME PROGRAMME MATRIK # DATE   Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3 2   EXPERIMENT 3   CLASS 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 Oscilloscope 2.2 Function generator 2.3 Voltmeter 2.4 Breadboard 2.5 Resistors: 10kΩ, 4.7kΩ, 1.0kΩ (3), 560Ω (1), 10Ω (2) 2.6 Capacitors: 2.2µF (2), 47µF (1) 2.7 Transistor 2N3904 3. INTRODUCTION Power amplifiers are used to deliver a large amount of power to a load. Typically, voltage amplifiers are cascaded together to amplify the input signal and the power amplifier will be the last stage of amplification. The class of an amplifier refers to the design of the circuitry within the amplifier. There are many classes 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” level circuit because they maintain low distortion. Distortion for class A power amplifiers increases as the signal 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 an amplifier. In many cases, it is more important to have the highest efficiency possible to deliver the most power to the load. The efficiency, η can be calculated using the following equations: η 󰀽 󰁐 󰁌 󰀯 󰁐 󰁓 󰀽 average power delivered to load / average power drawn from dc source   where: P S = V CC I Q P L   󰀽 󰁖 󰀲 󰀨󰁰󰁥󰁡󰁫󰀩 󰀯 󰀲󰁒 󰁌 󰀽 󰁖 󰀲󰁌󰀨󰁰󰁰󰀩 󰀯 󰀸󰁒 󰁌 I Q is the quiescent collector current V L(peak) is the peak value of a sinusoidal load voltage V L (p-p) is the peak –to–peak value of a sinusoidal load voltage     Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3 3   4. PROCEDURE : TABLE 1 4.1 DC Operation i) From Figure 1, do a pre-lab calculation for:  Assume β DC = 100 V BE(on) = 0.7 V a) V BB b) R B c) R E d) R C e) I B f) I C g) I E h) V CEQ ii) Connect the amplifier circuit. iii) Measure and record the values of V CC , V CEQ and I CQ . iv) Based from the measured values, sketch a DC load line (I C vs V CE ) . Indicate the major points.   Analogue Electronic I (EMT 249/112) Semester II 2013/2014 Exp . 3 4   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, calculate a) R L based on AC load line slope b) Find the new value of R loadV (Rl oadV 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 output voltage. The power amplifier operates at maximum undistorted output voltage. vii) Measure new values (after decreasing the input voltage): a) V in b) I in c) V out d) I out viii) Calculate the values of (to calculate power, the values must be in rms) a) P in , b) P out c) A P d) P IN(DC) ; Where V IN(DC)~ V CC and I IN(DC)~ I CQ e) Efficiency  
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