Table Of Content

Educational Systems CONCEPTS OF ELECTRONICS Book 2 Copyright © 1981 Thirteenth printing - 1985 Model EB-6140 Heath Company ~EATH COMPANY Not Affiliated with D.C. Heath Inc. All Rights Reserved ENTON HARBOR, MICHIGAN 49022 Printed in the United States of America 595-2585 ISBN0-87119-065-b Unit 3 ACTIVE DEVICES I 3-2 UNIT THREE CONTENTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Unit Objectives ............................................... 3-4 Solid-State Diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6 Transistors ................................................... 3-15 Field-Effect Transistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34 Optoelectronic Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-48 Integrated Circuits ........................................... 3-76 l I 3-3 Active Devices INTRODUCTION Basically, there are two types of components used in electronic circuits, passive and active devices. Passive devices do not alter their resistance, impedance or reactance when constant AC signals are applied to them. Examples of passive devices are resistors, inductors, and capacitors. Active devices, however, change their resistance or impedance when varying voltages are applied to them. As a result of this, active devices can amplify and rectify AC signals. Examples of active devices are vac uum tubes, transistors, and diodes. Let's take a brief look at the development of active devices. In the 1920's, the vacuum tube revolutionized the field of electronics, allowing the invention of many devices including the radio receiver. By 1950, solid state diodes and transistors, which are smaller and more rugged, started to replace vacuum tubes. The early 1960's saw the construction of groups of transistors and diodes on a single chip of silicon, forming an integrated circuit. The result of this development has been more compact and reliable electronic circuits and equipment. You will be studying several of these solid-state devices in this unit. The unit objectives listed on the next page state exactly what you are expected to learn from this unit. Study this list now and refer to it often as you study the text. 3-41 UNIT THREE UNIT OBJECTIVES When you complete this unit, you should be able to: 1. State the difference between P-type and N-type semiconductor materials. 2. Define depletion region. 3. Identify both forward and reverse-biased diodes. 4. Name the two most important solid-state diode ratings and define each one. 5. State the characteristics of zener and varactor diodes. 6. Identify the schematic symbols of a solid-state diode, a zener diode, and a varactor diode. 7. Identify the schematic symbols for NPN and PNP transistors. 8. Name the three sections of a transistor and identify them on a transistor schematic symbol. 9. State the correct bias for the emitter-base and collector-base junc tions of a transistor. 10. Identify and state the characteristics of the common-emitter, common-base, and common-collector amplifier configurations. 11. Define beta, thermal runaway, and maximum power dissipation as applicable to transistors. 12. Identify the schematic symbols of a JFET, a depletion mode MOS FET, and an enhancement mode MOSFET and name the terminals. I 3-5 Active Devices 13. State the difference between depletion and enhancement mode MOSFETs. 14. Name the three basic FET circuit configurations and state the characteristics of each circuit. 15. Define light, infrared rays, ultraviolet rays and photon. 16. State the light spectrum's frequency range. 17. Name four light sensitive devices, state the characteristics of each, and identify their schematic symbols. 18. State the basic operating principles of the light emitting diode (LED) and identify its schematic symbol. 19. Determine the necessary value of bias resistor for correct LED operation. 20. State the operating characteristics and modes of the liquid crystal display. 21. Define integrated circuit and list its advantages and disadvantages. 22. Name the two basic types of integrated circuits. 23. State the basic types and characteristics of digital !Cs. 24. State the basic characteristics of linear !Cs and the operational amplifier. 25. Find amplifier voltage gain when given input and output voltage. I 3-6 UNIT THREE 0~.e-=:-s,B SOLID-STATE DIODES ,,-,,80,\ -',- .\ I ,,, ,,, .... I~ , ' ~ \ Solid-state or semiconductor diodes have been in use since the earliest II If II I 4 + 'II ¢II ,II days of radio. However, recent advances have improved the semiconduc 1\ ~- ,\ I _ I ' \e .' , B' ',--9---,,-,..0" ',, , ,.0' I I tor diode, and specialized diodes such as the zener diode and variable ' ------~ capacitance diode have been developed. In this section, you will learn the SILICON basic principles of semiconductors. You will also study the solid-state diode. Semiconductor Materials In an earlier unit, a semiconductor was described as being neither a good conductor nor a good insulator. This is due to the atomic structure or more importantly, the valence or outer shell electrons. Figure 3-1 shows the atomic structure of the two semiconductors used in most solid-state devices: silicon and germanium. Note that both have 4 valence electrons. Compare this to the best conductors, which have one valence electron, or to the best insulators which have a full valence shell of eight electrons. Figure 3-1 Silicon and germanium, in their pure form, are actually worse conductors than is indicated by their four valence electrons. This is due to their The atomic structure of crystalline structure. A simplified diagram of the germanium crystal silicon and germanium. structure is shown in Figure 3-2. Note that only the valence electrons are shown. In the crystal structure, each of the four valence electrons of any one atom is shared with four neighboring atoms. Thus, each atom appears to have eight electrons in its valence shell. This fills each atom's valence shell and it becomes very difficult to free an electron for current flow. Figure 3-2 Simplified diagram of germanium crystal structure. I a- 7 Active Devices By adding carefully controlled quantities of certain impurities to.the pure semiconductor, its conductivity can be increased. This is called doping. An example of an impurity atom is arsenic, which has 5 valence elec trons. When it is added to a semiconductor crystal, only 4 of its 5 valence electrons can be fitted into the crystal structure. The additional fifth electron becomes free to act as a current carrier. This is shown in Figure 3-3. A crystal doped in this way is known as N-Type semiconductor material, since it contains additional electrons. Another impurity atom used to dope semiconductors is gallium. How ever, it has only three electrons. Therefore, when it is added to a semiconductor crystal a deficiency of electrons occurs. As shown in Figure 3-4, there now exists an area or hole in the crystal structure that lacks an electron. These holes behave as positively charged particles which are free to drift throughout the crystal. Due to the presence of the holes, the doped material is known as a P-Type semiconductor. While a hole is not actually positive, it is an area that a randomly drifting electron can "fall" into, thus completing the crystal structure. However, once an electron "falls" into a hole, another hole is created in the region from which the electron came. The movement of a hole in this way is equivalent to the movement of a positive charge equal to the negative charge carried by one electron. HOLE I" / .-g::G :e. f-=\« I.f ~g=Gef - \-lf t', ,.{»:iG::' . ;-' \~ I ~ \.'.v" -~~\ii)~ "C-:eI=D:::ee:: )fo:~=-C: I;.D::-e:" ~ I1'-1 OR II Ga 11 OR 11 s, ~ •=::a: "- s, ,~ '(•=[-)=e-:- ,t:-®==e,.: .,. ',((IDE I I OR *I I OR II OR I I ~ '«:S:1 :a' «.:S.:i ...' ~ -= S=i: : e.' ~ Figure 3-3 Figure 3-4 Semiconductor material doped with ar Semiconductor material doped with gal senic (N-Type). lium (P-Type). I 3-8 UNIT THREE P-N Junctions JUNCTION When N and P type semiconductor materials are grown together to form a / A single crystal, a solid-state diode results. This is shown in Figure 3-5A. 1N ~:11r, p I The area where the P and N type materials join is called the junction. As soon as the junction is formed, there will be a movement of electrons y DEPLETION across it. Electrons near the junction will move from the N-type material REGION into the P-type and fill the holes. As a result of this, the N-type material near the junction is depleted of electrons, while the P-type material near the junction is depleted of holes. Therefore, this area is called the deple tion region. B Figure 3-5B shows what happens when a battery is connected to the PN FORWARD BIAS junction. In this case, a negative voltage is applied to the N-type material, while a positive voltage is applied to the P-type. In this condition, once the voltage is above 1/2 to 1 volt, the applied voltage forces the electrons to cross the depletion region and continue across the P-type material. In DEPLETION other words, current flows through the diode and the depletion region no REGION ~ longer exists. This condition is called forward bias. Note that resistor R 1 C must be added to limit the current. This is because the voltage drop across the junction is very low. REVERSE BIAS Figure 3-5C shows what happens when the battery connections are re versed. There is no current flow and the depletion region becomes larger. This is because the negative voltage on the P-type material forces elec Figure 3-5 trons into the holes, thus depleting the region of still more holes. The Solid-state diode operation. positive voltage on the N-type material attracts the free electrons, which depletes the region of more electrons. This is called reverse-bias. The PN-junction acts as a one way switch because it conducts only when it is forward biased. It is called a solid-state diode. And, since it has a very low forward voltage drop, it makes an excellent rectifier. You will recall that a rectifier is used to convert alternating current into pulsating direct current. CATHODE ANO DE The schematic symbol for the solid-state diode is shown in Figure 3-6. I◄ The N-type material is called the cathode, while the P-type is the anode. The arrowhead in the schematic symbol points in the direction opposite to current flow. Note that when the solid-state diode is forward biased, • current flows from cathode to anode. CURRENT FLOW Figure 3-6 Schematic symbol for a solid-state diode.