16Chapter1IntroductionPRACTICE1.Assumethatonlythedigitsshown in8.75×2.446×9.15are significant.Deter-PROBLEMS4minetheirproductand show itwith thecorrectnumberof significantdigits.2.ForthenumbersofProblem1,determine8.75 X 2.4469.153.If the numbers in Problems 1 and 2 are exact,what are the answers to eightdigits?4. Three currents are measured as 2.36 A,11.5 A, and 452 mA. Only the digitsshown are significant.What is their sum shown to the correct number of sig-nificant digits?2. 2.34Answers:1.1963.195.83288;2.33907104.14.3 A1.7CircuitDiagramsElectric circuits are constructed using components such as batteries,switches,resistors,capacitors,transistors,interconnectingwires,etc.Torepresentthesecircuits on paper, diagrams are used. In this book, we use three types: blockdiagrams,schematicdiagrams,andpictorialsBlockDiagramsBlock diagrams describe a circuit or system in simplified form.The overallproblemisbrokenintoblocks,eachrepresentingaportion of the systemorcircuit.Blocks are labelled to indicate what they do or what they contain.then interconnected to showtheirrelationship to each other.General signalflowisusuallyfromlefttorightandtoptobottom.Figure1-5,forexample,representsan audio amplifier.Althoughyouhavenot covered anyof its cir-cuits yet,you should be able to follow the general idea quite easily-soundispicked up bythemicrophone,convertedto an electrical signal,amplifiedby apair of amplifiers,then outputtothe speaker,where it is converted backto sound. A power supply energizes the system. The advantage of a blockdiagram is that it gives you the overall picture and helps you understand thegeneral nature of a problem. However, it does not provide detail.SoundSoundPowerAmplifierAmplifierWavesWavest+MicrophonePowerSpeakerSupplyAmplificationSystemFIGURE1-5An exampleblockdiagram.Pictured is a simplified representation of an-audioamplificationsystem
1.7 Circuit Diagrams Electric circuits are constructed using components such as batteries, switches, resistors, capacitors, transistors, interconnecting wires, etc. To represent these circuits on paper, diagrams are used. In this book, we use three types: block diagrams, schematic diagrams, and pictorials. Block Diagrams Block diagrams describe a circuit or system in simplified form. The overall problem is broken into blocks, each representing a portion of the system or circuit. Blocks are labelled to indicate what they do or what they contain, then interconnected to show their relationship to each other. General signal flow is usually from left to right and top to bottom. Figure 1–5, for example, represents an audio amplifier. Although you have not covered any of its circuits yet, you should be able to follow the general idea quite easily—sound is picked up by the microphone, converted to an electrical signal, amplified by a pair of amplifiers, then output to the speaker, where it is converted back to sound. A power supply energizes the system. The advantage of a block diagram is that it gives you the overall picture and helps you understand the general nature of a problem. However, it does not provide detail. 16 Chapter 1 ■ Introduction PRACTICE PROBLEMS 4 1. Assume that only the digits shown in 8.75 2.446 9.15 are significant. Determine their product and show it with the correct number of significant digits. 2. For the numbers of Problem 1, determine 8.75 9 .15 2.446 3. If the numbers in Problems 1 and 2 are exact, what are the answers to eight digits? 4. Three currents are measured as 2.36 A, 11.5 A, and 452 mA. Only the digits shown are significant. What is their sum shown to the correct number of significant digits? Answers: 1. 196 2. 2.34 3. 195.83288; 2.3390710 4. 14.3 A Amplification System Sound Waves Microphone Speaker Sound Waves Power Supply Amplifier Power Amplifier FIGURE 1–5 An example block diagram. Pictured is a simplified representation of an audio amplification system.
17Section1.7CircuitDiagramsCurrentSwitchLamp(load)Interconnecting wireJoltBattery(source)FIGURE1-6A pictorial diagram.The battery is referred to as a source while the lampisreferredtoasaload.(The+and-onthebatteryare discussed in Chapter2.)SwitchPictorial DiagramsPictorial diagrams are one of thetypes of diagrams thatprovide detail.+BatteryLampTheyhelpyou visualize circuits and their operation byshowing componentsastheyactuallyappear.For example,thecircuit ofFigurel-6consists of abattery,aswitch,andanelectriclamp,all interconnectedbywire.Operationis easytovisualizewhen theswitchis closed, thebatterycauses currentin(a) Schematic using lamp symbolthe circuit, which lights the lamp.Thebattery is referred to as the source andthelamp as the load.SwitchSchematicDiagramsWhile pictorial diagrams help you visualize circuits, they are cumbersome todraw.Schematic diagrams get around this by using simplified, standardsymbolstorepresentcomponents;seeTable1-7.(Themeaning oftheseSBatteryResistancesymbolswill bemade clear as youprogressthroughthebook.)InFigureI-7(a),forexample,wehaveused someof thesesymbolstocreateaschematic for the circuit of Figure 1-6. Each component has been replacedby its correspondingcircuit symbol.(b) Schematic using resistance symbolWhen choosing symbols, choose those that are appropriate to the occa-sion.ConsiderthelampofFigure1-7(a).Aswewill showlater,thelampFIGURE1-7Schematicrepresentapossesses a property called resistance that causes it to resist the passage oftion of Figure 1-6.The lamp hasa cir-charge.Whenyouwishtoemphasizethisproperty,usetheresistancesymbolcuit propertycalled resistance (dis-rather than thelamp symbol, as inFigure1-7(b).cussed in Chapter3)
Pictorial Diagrams Pictorial diagrams are one of the types of diagrams that provide detail. They help you visualize circuits and their operation by showing components as they actually appear. For example, the circuit of Figure 1–6 consists of a battery, a switch, and an electric lamp, all interconnected by wire. Operation is easy to visualize—when the switch is closed, the battery causes current in the circuit, which lights the lamp. The battery is referred to as the source and the lamp as the load. Schematic Diagrams While pictorial diagrams help you visualize circuits, they are cumbersome to draw. Schematic diagrams get around this by using simplified, standard symbols to represent components; see Table 1–7. (The meaning of these symbols will be made clear as you progress through the book.) In Figure 1–7(a), for example, we have used some of these symbols to create a schematic for the circuit of Figure 1–6. Each component has been replaced by its corresponding circuit symbol. When choosing symbols, choose those that are appropriate to the occasion. Consider the lamp of Figure 1–7(a). As we will show later, the lamp possesses a property called resistance that causes it to resist the passage of charge. When you wish to emphasize this property, use the resistance symbol rather than the lamp symbol, as in Figure 1–7(b). Section 1.7 ■ Circuit Diagrams 17 Jolt Battery (source) Switch Current Lamp (load) Interconnecting wire FIGURE 1–6 A pictorial diagram. The battery is referred to as a source while the lamp is referred to as a load. (The and on the battery are discussed in Chapter 2.) FIGURE 1–7 Schematic representation of Figure 1–6. The lamp has a circuit property called resistance (discussed in Chapter 3). Switch Switch (b) Schematic using resistance symbol (a) Schematic using lamp symbol Battery Lamp Battery Resistance
18Chapter1IntroductionTABLE1-7Schematic Circuit Symbols1ACSingleMulticellCurrentFixedVariableFixedVariableAirIronFerritecellVoltageSourceCoreCoreCoreSourceBatteriesResistorsCapacitorsInductors+SPSTEarth1TChassisSPDTWiresWiresLampSwitchesMicrophoneSpeakerJoiningCrossingGroundsFusesVoltmeterVAmmeterAirCoreIron CoreFerriteCoreCircuitDependentBreakersTransformersSourceAmmeterWhenyou drawschematicdiagrams,drawthemwithhorizontal andver-tical lines joined at right angles as in Figure 1-7. This is standard practice(Atthispointyou should glancethrough somelater chapters,e.g.,Chapter7.and studyadditional examples.)1.8CircuitAnalysis Using ComputersPersonal computers areused extensivelyfor analysis and design.Softwaretools available for such tasks fall into two broad categories:prepackagedapplicationprograms(applicationpackages)andprogramminglanguages.Application packages solve problems without requiring programming onthe part of the user, while programming languages require the user to writecodeforeachtypeofproblemtobesolved.CircuitSimulation SoftwareSimulation softwareis application software;it solvesproblemsby simulatingthebehavior of electrical and electronic circuits rather than by solving setsofequations.To analyze a circuit,you“buildit on your screen by selectingcomponents(resistors,capacitors,transistors,etc.)fromalibraryofparts,which youthen position and interconnect toform thedesired circuit.You can
When you draw schematic diagrams, draw them with horizontal and vertical lines joined at right angles as in Figure 1–7. This is standard practice. (At this point you should glance through some later chapters, e.g., Chapter 7, and study additional examples.) 1.8 Circuit Analysis Using Computers Personal computers are used extensively for analysis and design. Software tools available for such tasks fall into two broad categories: prepackaged application programs (application packages) and programming languages. Application packages solve problems without requiring programming on the part of the user, while programming languages require the user to write code for each type of problem to be solved. Circuit Simulation Software Simulation software is application software; it solves problems by simulating the behavior of electrical and electronic circuits rather than by solving sets of equations. To analyze a circuit, you “build” it on your screen by selecting components (resistors, capacitors, transistors, etc.) from a library of parts, which you then position and interconnect to form the desired circuit. You can 18 Chapter 1 ■ Introduction Single cell Multicell Batteries AC Voltage Source Current Source Fixed Resistors Capacitors Inductors Grounds Fuses Wires Crossing Wires Lamp Joining SPST SPDT Switches Microphone Voltmeter Ammeter Ammeter Transformers Air Core Iron Core Ferrite Core Circuit Breakers Dependent Source Speaker Chassis Earth Variable Fixed Variable Air Core Iron Core Ferrite Core V I A kV TABLE 1–7 Schematic Circuit Symbols
19Section1.8CircuitAnalysisUsingComputers口区Electronics Workbench Educational EditiorEile Edit Cicut Analyete WindowHelb日国eQ%a？富国M酒Pure2艾蓝艺国2RO100u6.8 km50uA2.0022μ50u-100u12u24u36u48u606.84FIGURE 1-8 Computer screen showing circuit analysis using Electronics Workbench.changecomponentvalues,connections,andanalysisoptionsinstantlywiththe click of a mouse.Figures 1-8 and 1-9 showtwoexamples.Most simulation packages use a software engine called SPICE, an acro-nymfor Simulation Program with Integrated Circuit Emphasis.Popularproducts arePSpice,ElectronicsWorkbench(EWB)and CircuitMakerInthistext,weuseElectronicsWorkbenchandOrCADPSpice,bothofwhichhave eitherevaluation or studentversions (see thePrefaceformoredetails)Both products have their strong points. Electronics Workbench, for instance,morecloselymodelsanactualworkbench(completewithrealisticmeters)thandoesPSpiceandisabiteasiertolearn.Ontheotherhand.PSpicehasa0OiCADCaplure-(SCHEMATIC1:PAGE11axFle Edt Yiew Place Macro Papioe Accessoies Dptions indow Helbe0aS0224TCLOSE=0R1X2WU1AV1C1一国10V2000uFLVU(C1:1T0国10 kemnst selectedScale=200%X-2.30 Y=1.50ReadFIGURE1-9Computer screen showingcircuit analysisusing OrCADPSpice
change component values, connections, and analysis options instantly with the click of a mouse. Figures 1–8 and 1–9 show two examples. Most simulation packages use a software engine called SPICE, an acronym for Simulation Program with Integrated Circuit Emphasis. Popular products are PSpice, Electronics Workbench® (EWB) and Circuit Maker. In this text, we use Electronics Workbench and OrCAD PSpice, both of which have either evaluation or student versions (see the Preface for more details). Both products have their strong points. Electronics Workbench, for instance, more closely models an actual workbench (complete with realistic meters) than does PSpice and is a bit easier to learn. On the other hand, PSpice has a Section 1.8 ■ Circuit Analysis Using Computers 19 FIGURE 1–8 Computer screen showing circuit analysis using Electronics Workbench. FIGURE 1–9 Computer screen showing circuit analysis using OrCAD PSpice
20Chapter1Introductionmore complete analysis capability; for example, it determines and displaysimportant information (such as phase angles in ac analyses and currentwaveforms in transient analysis) that Electronics Workbench, as of this writ-ing, does not.Prepackaged Math SoftwareMath packages also require no programming. A popular product is Mathcadfrom Mathsoft Inc. With Mathcad, you enter equations in standard mathe-matical notation. For example, to find the first root of a quadratic equation,you would use-b+Vb-4.a.cx: =-2 .aMathcad is a great aid for solving simultaneous equations such as thoseencountered during mesh or nodal analysis (Chapters 8 and 19) and for plot-tingwaveforms.(You simplyentertheformula.)Inaddition,Mathcad incor-porates a built-in Electronic Handbook that contains hundreds of useful for-mulas andcircuit diagrams thatcan saveyouagreat deal of time.Programming LanguagesMany problems can also be solved using programming languages such asBASIC, C, or FORTRAN. To solve a problem using a programming lan-guage, you code its solution, step by step.We do not consider programminglanguages in this book.AWord of CautionWith the widespread availability of inexpensive software tools, you maywonderwhyyou are askedto solveproblemsmanuallythroughoutthisbook.The reason is that, as a student, your job is to learn principles and concepts.Getting correct answers using prepackaged software does not necessarilymeanthatyouunderstandthetheoryitmaymean onlythatyouknowhowto enter data. Software tools should always be used wisely.Before you usePSpice,ElectronicsWorkbench,or anyotherapplicationpackage,be surethat you understand the basics of the subject that you are studying.This iswhyyou should solveproblems manuallywith your calculatorfirst.Follow-ingthis,try someoftheapplicationpackagesto exploreideas.Mostchapters(starting with Chapter 4)includea selection of worked-out examples andproblems to get you started
more complete analysis capability; for example, it determines and displays important information (such as phase angles in ac analyses and current waveforms in transient analysis) that Electronics Workbench, as of this writing, does not. Prepackaged Math Software Math packages also require no programming. A popular product is Mathcad from Mathsoft Inc. With Mathcad, you enter equations in standard mathematical notation. For example, to find the first root of a quadratic equation, you would use x: Mathcad is a great aid for solving simultaneous equations such as those encountered during mesh or nodal analysis (Chapters 8 and 19) and for plotting waveforms. (You simply enter the formula.) In addition, Mathcad incorporates a built-in Electronic Handbook that contains hundreds of useful formulas and circuit diagrams that can save you a great deal of time. Programming Languages Many problems can also be solved using programming languages such as BASIC, C, or FORTRAN. To solve a problem using a programming language, you code its solution, step by step. We do not consider programming languages in this book. A Word of Caution With the widespread availability of inexpensive software tools, you may wonder why you are asked to solve problems manually throughout this book. The reason is that, as a student, your job is to learn principles and concepts. Getting correct answers using prepackaged software does not necessarily mean that you understand the theory—it may mean only that you know how to enter data. Software tools should always be used wisely. Before you use PSpice, Electronics Workbench, or any other application package, be sure that you understand the basics of the subject that you are studying. This is why you should solve problems manually with your calculator first. Following this, try some of the application packages to explore ideas. Most chapters (starting with Chapter 4) include a selection of worked-out examples and problems to get you started. b b2 4ac 2 a 20 Chapter 1 ■ Introduction