culture+整套课件完整版电子教案最全PPT整本书课件全套教学教程.pptx

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1、Unit 1 Basis of Electric CircuitsElectric circuitsThe elements that comprise the circuit model are called ideal circuit components.An ideal circuit component is a mathematical model of an actual electrical component,like a battery or a light bulb.It is important for the ideal circuit component used

2、in a circuit model to represent the behavior of the actual electrical component to an acceptable degree of accuracy.The tools of circuit analysis,the focus of this unit,are then applied to the circuit.下一页返回Unit 1 Basis of Electric CircuitsCircuit analysis is based on mathematical techniques and is u

3、sed to predict the behavior of the circuit model and its ideal circuit components.A comparison between the desired behavior,from the design specifications,and the predicted behavior,from circuit analysis,may lead to refinements in the circuit model and its ideal circuit elements.Once the desired and

4、 predicted behaviors are in agreement,a physical prototype can be constructed.下一页上一页返回Unit 1 Basis of Electric CircuitsThe physical prototype is an actual electrical system,constructed from actual electrical components.Measurement techniques are used to determine the actual,quantitative behavior of

5、the physical system.This actual behavior is compared with the desired behavior from the design specifications and the predicted behavior from circuit analysis.The comparisons may result in refinements to the physical prototype,the circuit model,or both.Eventually,this iterative process,in which mode

6、ls,components,and systems are continually refined,may produce a design that accurately matches the design specifications and thus meets the need.下一页上一页返回Unit 1 Basis of Electric Circuits From this description,it is clear that circuit analysis plays a very important role in the design process.Because

7、 circuit analysis is applied to circuit models,practicing engineers try to use mature ciruit models so that the resulting designs will meet the design specifications in the first iteration.In this unit,we use models that have been tested for between 20 and 100 years;you can assume that they are matu

8、re.The ability to model actual electrical systems with ideal circuit elements makes circuit theory extremely useful to engineers.下一页上一页返回Unit 1 Basis of Electric CircuitsSaying that the interconnection of ideal circuit elements can be used to quantitatively predict the behavior of a system implies t

9、hat we can describe the interconnection with mathematical equations.For the mathematical equations to be useful,we must write them in terms of measurable quantities.In the case of circuits,these quantities are voltage and current.The study of circuit analysis involves understanding the behavior of e

10、ach ideal circuit element in terms of its voltage and current and understanding the constraints imposed on the voltage and current as a result of interconnecting the ideal elements.下一页上一页返回Unit 1 Basis of Electric CircuitsCircuit analysis is based on the variables of voltage and current.Voltage is t

11、he energy per unit charge created by charge separation and has the SI unit of volt v=dw/dq.Current is the rate of charge flow and has the SI unit of ampere(i=dq/dt).The ideal basic circuit element is a twoterminal component that cannot be subdivided;it can be described mathematically in terms of its

12、 terminal voltage and current.The passive sign convention uses a positive sign in the expression that relates the voltage and current at the terminals of an element when the reference direction for the current through the element is the direction of the reference voltage drop across the element下一页上一

13、页返回Unit 1 Basis of Electric CircuitsPower is energy per unit of time and is equal to the product of the terminal voltage and current;it has the SI unit of watt.The algebraic sign of power is interpreted as follows:If p0,power is being delivered to the circuit or circuit component.If p0,power is bein

14、g extracted from the circuit or circuit component.下一页上一页返回Unit 1 Basis of Electric CircuitsThe circuit elements introduced in this chapter are voltage sources,current sources,and resistors.An ideal voltage source maintains a prescribed voltage regardless of the current in the device.An ideal current

15、 source maintains a prescribed current regardless of the voltage across the device.Voltage and current sources are either independent,that is,not influenced by any other current or voltage in the circuit;or dependent,that is,determined by some other current or voltage in the circuit.下一页上一页返回Unit 1 B

16、asis of Electric CircuitsA resistor constrains its voltage and current to be proportional to each other.The value of the proportional constant relating voltage and current in a resistor is called its resistance and is measured in ohms.Ohms Law establishes the proportionality of voltage and current i

17、n a resistor.Specifically V=IR if the current flow in the resistor is in the direction of the voltage drop across it,orV=-IRif the current flow in the resistor is in the direction of the voltage rise across it.下一页上一页返回Unit 1 Basis of Electric CircuitsBy combining the equation for power,p=vi,with Ohm

18、s Law,we can determine the power absorbed by a resistorCircuits are described by nodes and closed paths.A node is a point where two or more circuit elements join.When just two elements connect to form a node,they are said to be in series.A closed path is a loop traced through connecting elements,sta

19、rting and ending at the same node and encountering intermediate node only once each.下一页上一页返回Unit 1 Basis of Electric CircuitsA circuit is said to be solved when the voltage across and the current in every element have been determined.Ohms Law is an important equation for deriving such solutions.In s

20、imple circuit structures,Ohms Law is sufficient for solving for the voltages across and the current in every element.However,for more complex interconnection we need to use two more important algebraic relationships,known as Kirchhoffs Law,to solve for all the voltage and current.下一页上一页返回Unit 1 Basi

21、s of Electric CircuitsThe Kirchhoffs Current Law is：The algebraic sum of all the currents at any node in a circuit equals zero.The Kirchhoffs Voltage Law is：The algebraic sum of all the voltages across any closed path in a circuit equals zero.下一页上一页返回Unit 1 Basis of Electric CircuitsTechnology of ci

22、rcuit analysisSo far,we have analyzed relatively simple resistive circuits by applying Kirchhoffs laws in combination with Ohms Law.We can use this approach for all circuits,but as they become structurally more complicated and involve more and more elements,this direct method soon becomes cumbersome

23、.In this lesson we introduce two powerful techniques of circuit analysis that aid in the analysis of complex circuit structures：下一页上一页返回Unit 1 Basis of Electric Circuitsthe node voltage method and the mesh current method.These techniques give us two systematic methods of describing circuits with the

24、 minimum number of simultaneous equations.The final topic in this lesson considers the conditions necessary to ensure that the power delivered to a resistive load by a source is maximized.There in equivalent circuits are used in establishing the maximum power transfer conditions.下一页上一页返回Unit 1 Basis

25、 of Electric CircuitsIntroduction to the node voltage methodWe introduce the node voltage method by using the essential nodes of the circuit.The first step is to make a neat layout of the circuit so that no branches cross over and to make clearly the essential nodes on circuit diagram.If the circuit

26、 has N essential nodes,therefore,we need(N-1)node voltage equations to describe the circuit.The next step is to select one of the N essential nodes as a reference node.Although theoretically the choice is arbitrary,practically the choice for the reference node often is obvious.下一页上一页返回Unit 1 Basis o

27、f Electric CircuitsFor example,the node with the most branches is usually a good choice.The optimum choice of the reference node will become apparent after you have gained some experience using this method.After selecting the reference node,we define the node voltage on the node voltages on the circ

28、uit diagram.A node voltage is defined as the voltage rise from the reference node to a nonreference node.下一页上一页返回Unit 1 Basis of Electric CircuitsWhen a voltage source is the only elements between two essential nodes,the node voltage method is simplified.As an example,look at the circuit in Figure 1

29、.1.1.There are four essential nodes in this circuit,which means that three simultaneous equations are needed.From these four essential nodes,a reference node has been chosen and three other nodes have been labeled.下一页上一页返回Unit 1 Basis of Electric CircuitsBut the 36 V source constraints the voltage b

30、etween node 1 and node 2 to 36V.This means that the current that flows from node 1 to node 2 will be added to the equations.We are now ready to generate the node voltage equations.In general,when a voltage source is the only elements between two essential nodes,the node voltage method requires some

31、additional manipulations.下一页上一页返回Unit 1 Basis of Electric CircuitsIntroduction to the mesh current methodAs stated in this lesson,the mesh current method of circuit analysis enables us to describe a circuit.A mesh current is the current that exists only in the perimeter of a mesh.On a circuit diagra

32、m it appears as either a closed solid line or an almost closed solid line that follows the perimeter of the appropriate mesh.An arrowhead on the solid line indicates the reference direction for the mesh current.Note that by definition,mesh currents automatically satisfy Kirchhoffs current law.That i

33、s,at any nodes in the circuit,a given mesh current both enters and leaves the node.下一页上一页返回Unit 1 Basis of Electric CircuitsWhen a branch includes a current source,the mesh current method requires some additional manipulations.The circuit shown in Figure 1.1.2 depicts the nature of the problem.We ar

34、e now ready to generate the mesh current equations.In general,when you use the mesh current method to solve circuits that have a branch including a current source,the number of the equations is reduced.上一页返回Figure 1.1.2 An example of mesh current method返回Figure 1.1.1 An example of node voltage metho

35、d返回Unit 2 Analog CircuitsAnalog circuits operate with currents and voltages that vary continuously with time and have no abrupt transitions between levels.Generally speaking,analog circuits are contrasted with digital circuits that function as though currents or voltages existed only at one of a set

36、 of discrete levels,all transitions between levels being ignored.Since most physical quantities,e.g.,velocity and temperature,vary continuously,as does audio,an analog circuit provides the best means of representing them.下一页返回Unit 2 Analog CircuitsHowever,digital circuits are often preferred because

37、 of the ease with which their outputs can be manipulated by computers,and because digital signals are more robust and less subject to transmission errors.There are special analogto digital and digital to analog circuits to convert from one type of signal to the other.下一页上一页返回Unit 2 Analog CircuitsTh

38、e circuits in this unit make use of IC,or integrated circuit,components.Such components are actually networks of interconnected components manufactured on a single wafer of semiconducting material.Integrated circuits providing a multitude of pre-engineered functions are available at a very low cost,

39、benefiting students,hobbyists and professional circuit designers alike.Most integrated circuits provide the same functionality as“discrete”semiconductor circuits at higher levels of reliability and at a fraction of the cost.Usually,discrete component circuit construction is favored only when power d

40、issipation levels are too high for integrated circuits to handle.下一页上一页返回Unit 2 Analog CircuitsPerhaps the most versatile and important analog integrated circuit for the student to master is the operational amplifier,or op-amp.Essentially nothing more than a differential amplifier with very high vol

41、tage gain,op-amps are the workhorse of the analog design world.By cleverly applying feedback from the output of an op-amp to one or more of its inputs,a wide variety of behaviors may be obtained from this single device.Many different models of op-amps are available at a low cost,but circuits describ

42、ed in this unit will incorporate only commonly available op-amp models.下一页上一页返回Unit 2 Analog CircuitsBasic analog circuitsResistance:Resistance can be defined as the characteristic of a medium that opposes flow of current through itself.As illustrated in Figure 1.2.1,the unit of resistance is ohms w

43、hich is represented by the Greek letter (Omega).The power value associated with resistance is quantified as the amount of power that the resistor can dissipate as heat without overheating itself.下一页上一页返回Unit 2 Analog CircuitsThe current I through the resistor R is defined as:For a 1 Mega ohm resista

44、nce,the current resulting from the application of 10V would be 10 micro-amperes.下一页上一页返回Unit 2 Analog CircuitsOhms Law is the fundamental equation that describes the above relationship between voltage potential,the current flowing in the circuit,and the resistance of the circuit.The power dissipated

45、 in a load resistance R is defined as the product of the current and the voltage.Other relationships for power can be easily derived from this by applying Ohms Law and substituting.下一页上一页返回Unit 2 Analog CircuitsNote:Digital multimeters(DMMs)are the most common measurement devices found in automated

46、test systems.DMMs are usually simple to use and are often low cost instruments.Generally,DMMs have built in conditioning that provides:high resolution(commonly measured in digits);multiple measurements(volts,current,resistance,etc.);isolation and high voltage capabilities.下一页上一页返回Unit 2 Analog Circu

47、itsCapacitors:Capacitors store energy in the form of electrical charge.The amount of charge that the capacitor can hold depends on the area of the two plates in Figure 1.2.2 and the distance between them.Large plates with a small distance between them have a higher capacity to hold charge.The electr

48、ic field between the plates of a capacitor resists changes in applied voltage.Capacitors decrease their resistance with frequency.下一页上一页返回Unit 2 Analog CircuitsReading capacitor values:The unit of capacitance,as shown in Figure 1.2.2,is Farad which is represented by the letter F.The formula to calcu

49、late capacitance is:下一页上一页返回Unit 2 Analog CircuitsInductance:Inductance is defined as the amount of voltage dropped across the inductor for a given rate of change of current flowing through it.Inductors increase their resistance with frequency.The unit of inductance is Henry which is represented by

50、the letter H.下一页上一页返回Unit 2 Analog CircuitsImpedance:Impedance Z is generally defined as the total opposition a device or circuit offers to the flow of an alternating current(AC)at a given frequency.Its value is equal to the ratio between the voltage and the current over an element of a circuit.Ther