The Audio Amplifier

# The Audio Amplifier - Page 1 of 11 ELCT 301 Lab Report #4...

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Page 1 of 11 ELCT 301 Lab Report #4 Class B and Class AB Audio Amplifier ___________________ Jared Tucker Department of Electrical Engineering University of South Carolina Columbia, SC 29208

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Page 2 of 11 Laboratory Grade: Pre-lab computation ____ of 10 Technical Content ____ of 60 Format/Presentation Clarity ____ of 20 Other ____ of 10 Late Deductions ____ ____ of 100 Student Comments: Grader Comments:
Page 3 of 11 Class B and Class AB Audio Amplifier I. Introduction The primary focus of this lab was to observe operating characteristics of several different amplifiers. The lab required me to construct an A, B and AB amplifier. After constructing the amplifiers, I am to measure how the different configurations of the amplifiers affect an AC signal. It will be proved analytically and by experiment the affects of closed and open loop gain play a major role in affecting the output of the amplifiers. II. Theory Amplifiers increase the power level of an ac input by transferring the power from the dc power supply to the input signal. The transistors are taking the parallel rail voltages and combining them at the center line, increasing the gain. Each type of amplifier configuration has its advantages and drawbacks. The two major factors that should be considered in design are efficiency and distortion. Our main concern will be the distortion properties. Class A amplifiers are typically the most common configuration used in the electronics field . 1 Therefore, class A amplifier analysis is a good place to start. Class A amplifiers contain a transistor that conducts during the entire cycle of the input. They have an output that contains little or no distortion and have a maximum theoretical efficiency of 25%. Because of their relatively poor efficiency ratings, class A amplifiers are generally used as small-signal (low-power) amplifiers. Small-signal amplifiers are primarily used to drive higher-power stages. The class B amplifier typically contains two transistors that are connected as shown in Figure (1). Figure 1. Class B amplifier. Each transistor in this type of amplifier conducts during one alternation of the ac input cycle and is in cutoff during the other alternation. One transistor conducts during the negative alternation of the ac input and the other conducts during the positive alternation. A complete 360° output waveform is produced. The class B amplifier contains two transistors that are biased at cutoff (each conducting during one alternation of the ac input cycle). However, the B amplifier is classic for having a specific type of distortion Figure (2).

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Page 4 of 11 I ( RE_ N) I ( RE_ P) - 200mA 0A 200mA SEL>> Fr equency 0Hz 10KHz 20KHz 30KHz 40KHz 50KHz 60KHz 70KHz V( 12) 0V 0. 5V 1. 0V (a) Class B Outpu, V vs. Time (b)Class B Fourier analysis Figure 2. Class B Transient and Frequency Characteristics.
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## This note was uploaded on 04/28/2008 for the course EE ELCT 301 taught by Professor Santi during the Spring '08 term at University of South Carolina Beaufort.

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The Audio Amplifier - Page 1 of 11 ELCT 301 Lab Report #4...

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