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Unformatted text preview: G. Rizzoni, Principles and Applications of Electrical Engineering Problem solutions, Chapter 12 12.1 Chapter 12 Instructor Notes Chapter 12 introduces the subject of power electronics. The importance of power electronics cannot be overemphasized, considering the widespread industrial application of electric machines, and other high current loads in practical engineering applications. The chapter discusses the basic characteristics and limitations of power amplifiers, practical voltage regulators, inductive loads (such as electric motors), and SCRs. The aim is to give the student sufficient understanding of the device characteristics to be able to complete simple "order of magnitude" calculations to be able to size a device for a given application. This chapter is much more practically oriented than some of the others in the text, and may be used to accompany a course in electric power and machines based on Chapters 7, 16, 17 and 18. After Sections 12.1 and 12.2 present a classification of power electronic devices (Figure 12.1, p. 578) and circuits (Table 12.1, p. 579), the discussion is divided into the topics of Voltage Regulators (Section 12.3), Power Amplifiers and Transistor Switches (Section 12.4), Rectifiers and Controlled Rectifiers (Section 12.5), and Electric Motor Drives (Section 12.6) Homework problems are divided into three major sections. The first, on voltage regulators, includes problems two different voltage regulator circuits (12.2, 12.3) The second, on rectifiers and controlled , illustrates a battery charging circuit (12.7) and two simple motor speed control problems (12.9, 12.10). The last section, on drives, introduces choppers, and more advanced problems on DC motor supplies based on controlled rectifiers (12.23 and 12.24). Learning Objectives 1. Learn the classification of power electronic devices and circuits. Sections 1 and 2. 2. Analyze the operation of practical voltage regulators. Section 3 . 3. Understand the principal limitations of transistor power amplifiers. Section 4 . 4. Analyze the operation of single and threephase controlled rectifier circuits. Section 5 . 5. Understand the operation of power converters used in electric motor control, and perform simplified analysis on DCDC converters. Section 6 . G. Rizzoni, Principles and Applications of Electrical Engineering Problem solutions, Chapter 12 12.2 Section 12.3: Voltage Regulators Problem 12.1 Solution: Find: Repeat Example 12.1 for a 7V Zener diode. Analysis: Calculating the collector and base currents according to: mA 8 . 51 11 A 57 . 10 3 . 1 7 = = = = E B E I I I We find: V 6 . V 3 . 14 7 . 5 20 20 A 225 . A 277 . 47 7 20 > = = = = = = = L CE B R Z R V V I I I I Thus, the transistor is in the active region. The Zener power is: W 576 . 1 = Z Z V I ....
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This note was uploaded on 04/08/2009 for the course ELE ELE1403 taught by Professor Khaled during the Spring '09 term at NYU Poly.
 Spring '09
 Khaled

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