Understanding Transistors

Chapter Understanding Transistors

Complete Electronics Self Teaching Guide with Projects
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Summary of Contents

Complete Electronics Self Teaching Guide with Projects

  • CHAPTER 3 INTRODUCTION TO THE TRANSISTOR92“The Transistor Switch,” and Chapter 8, “Transistor Amplifiers”) illustrates how BJTs and JFETs function and how they are used in electronic circuits. Because JFETs and MOSFETs function in similar fashion, MOSFETs are not covered here.Projects in this chapter can help you to build a simple one-transistor circuit. You can easily set up this circuit on a home workbench. You should take the time to obtain the few components required, and actually build and operate the circuit.In Chapter 4, you continue to study transistor circuits and the operation of the tran-sistor as a switch. In Chapter 8, you learn how a transistor can be made to operate as an amplifier. In this mode, the transistor produces an output that is a magnified version of an input signal, which is useful because many electronic signals require amplification. These chapters taken together present an easy introduction to how transistors function, and how they are used in basic electronic circuits.When you complete this chapter, you can do the following: ■ Describe the basic construction of a BJT. ■ Describe the basic construction of a JFET. ■ Specify the relationship between base and collector current in a BJT. ■ Specify the relationship between gate voltage and drain current in a JFET. ■ Calculate the current gain for a BJT. ■ Compare the transistor to a simple mechanical switch.UNDERSTANDING TRANSISTORS1  The diagrams in Figure 3.1 show some common transistor cases (also called packages). The cases protect the semiconductor chip on which the transistor is built and provide leads that can be used to connect it to other components. For each transistor, the dia-grams show the lead designations and how to identify them based on the package design. Transistors can be soldered directly into a circuit, inserted into sockets, or inserted into breadboards. When soldering, you must take great care because transistors can be destroyed if overheated. A heat sink clipped to the transistor leads between the solder joint and the transistor case can reduce the possibility of overheating. If you use a socket, you can avoid exposing the transistor to heat by soldering the connections to the socket before inserting the transistor.Book Authorc03V107/04/2012 2:56 PM c03.indd 927/4/2012 3:04:23 PM