电路理论第一章

1、1董维杰董维杰 电子科学与技术学院电子科学与技术学院Email: Phone:qq：576491634 Office: B405Circuit Theory电路理论电路理论2 Faculty of Electronic Information and Electrical Engineering? What is the basic quantities to represent electronic information? voltage and current What is the carrier of voltage and current ?3Introd

2、uctionIntroduction Circuit? Circuit examples Functions of Circuits Why study Circuit Theory？(目的目的) Content of the course （内容）（内容） How to study Circuit Theory？（方法）？（方法） Plan and demand to the course Reference books and websites41 Circuit and Examples1 Circuit and ExamplesAn electric circuit is an int

3、erconnection of electrical elements.Electrical system/电力系统电力系统Electronic circuit/电子电路电子电路5发电站电力网水库河流大坝进水口发电机水轮机水利发电厂水利发电厂6三峡工程首台机组三峡工程首台机组2号机转子吊装到位。号机转子吊装到位。 其最大直其最大直径径18.4米，高米，高3.4米，重米，重1694.5吨，单机容量吨，单机容量70万千瓦。万千瓦。 2号机组是首台发电机组，已于号机组是首台发电机组，已于2003年年7月投产发电，月投产发电，7 家用电器家用电器 电磁炉电磁炉微波炉微波炉热水器热水器8 办公与消费类设

4、备办公与消费类设备 传真机传真机 计算机计算机 复印机复印机 9 仪器仪表仪器仪表 电子体温计电子体温计电子量匙电子量匙辐射测量仪辐射测量仪出租车计价器出租车计价器跑步机面板跑步机面板10Electronic Electronic productsproductsCircuit boardCircuit boardCircuit elementsn分立件分立件individual devicesn集成电路集成电路 IC11Integrated circuit/Integrated circuit/集成电路集成电路12Circuit elements/Circuit elements/电路元件电

5、路元件电阻电阻电容电容电感电感二极管二极管电池电池三三极极管管电阻电阻电容电容13Real circuits/Real circuits/实际电路实际电路电源电源收音机收音机142 2、Functions of Functions of CircuitsCircuits Generate Transform Consume (1)energy(1)energy Produce Processing Measure Display Store (2)information(2)information15专业课专业课电类通识课电类通识课3 3 Why study Circuit Theory?计算

6、机原理计算机原理通信原理通信原理信号信号与系与系统统数字数字电路电路模拟模拟电路电路电路电路理论理论电路理论：学习电路的电路理论：学习电路的基本概念基本概念、基本定律基本定律及及基本电基本电路分析的方法；路分析的方法；电路理论是学习模拟电路、数字电路、通信电路、微机原理的基础课电路理论是学习模拟电路、数字电路、通信电路、微机原理的基础课数字集成电路设计数字集成电路设计电力拖动电力拖动16电路理论电路理论 (Circuit Theory, Electrical Network Theory) “电路理论电路理论” 是研究电与磁系统的理论，该理论用是研究电与磁系统的理论，该理论用积分量描述电与磁现

7、象。积分量描述电与磁现象。 电磁场相关的积分量例如有：电磁场相关的积分量例如有：电压、电流、电荷、电压、电流、电荷、磁通、磁压、磁链。磁通、磁压、磁链。电路理论包括：电路理论包括：电路分析：已知电路结构、参数，分析电路特性。电路分析：已知电路结构、参数，分析电路特性。电路综合：已知电路特性，确定电路结构和参数。电路综合：已知电路特性，确定电路结构和参数。故障诊断：已知正常和故障情况下的特性，确定故障故障诊断：已知正常和故障情况下的特性，确定故障 类型、故障位置和故障参数。类型、故障位置和故障参数。174 4 Content of the courseConstitutePhasor Analy

8、sisAlternative Circuit-Direct Circuit-Transient CircuitOhms law;Element laws;Kirchhoffs law:KCL;KVL;Theorems:Superposition; Thevenin;Substitute;Components:R; L; C; Vs; Is3 Types of Circuit Follow Analysis methods:Equivalent transform;Nodal analysis;Mesh analysis;Directly applied to analysisFollow Fo

9、llow 185 5 How to study Circuit Theory？ Concept: get the idea in the lectures Compute: do homework, practise more Compare: work in labs to see Communicate: work in groups, discuss Conclude/ summarize196 Plan and demand(1) Assessment quiz and homework: 10% midterm test (chapter 15): 20% final test (c

10、hapter 111): 70%(2)答答 疑：疑： 课外：创新园大厦课外：创新园大厦 B405； 课内（研讨课）：教室或实验室课内（研讨课）：教室或实验室(3)考勤考勤： 课前完成各种请假课前完成各种请假( (提供证明提供证明) )，否则无效；，否则无效； 课上课上1 1道测验题道测验题20陈希有，电路分析基础，陈希有，电路分析基础，2004，高等教育出版社，高等教育出版社燕庆明，电路分析教程，燕庆明，电路分析教程，2003，高等教育出版社，高等教育出版社Fundamentals of Electric Circuits, Charles K. Alexander, 清华大学出版社，清华大学

11、出版社，2000Fundamentals of Electric Circuit Analysis，Clayton Paul, 2001, (73.76 P324A#)Introductory Circuit Analysis, R L Boylestad, 1997，(73.112 B792-8#), 另有影印版，高等教育出版社，另有影印版，高等教育出版社，2002Electric Circuits, 6th Ed, James W. Nilsson, 2003, 科科学出版社，另有译本电路，电子工业出版社，学出版社，另有译本电路，电子工业出版社，20027 Reference Books

12、and Web21 本课程网址本课程网址 http:/ 辽宁省精品课辽宁省精品课电路理论电路理论n 麻省理工公开课：电路和电子学麻省理工公开课：电路和电子学n http:/ 上海交通大学国家级精品课程网站上海交通大学国家级精品课程网站 http:/ 基础电路理论基础电路理论 西安交通大学国家级精品课程网站西安交通大学国家级精品课程网站 http:/ 中国开放教育资源中国开放教育资源 http:/ Voltage and current reference directions 电压、电流的参考方向电压、电流的参考方向2. Voltage-Current Characteristics of C

13、ircuit elements 电路元件特性电路元件特性3. Kirchhoffs Laws 基尔霍夫定律基尔霍夫定律Chapter1 Circuit Elements and Circuit Laws 电路元件和电路定律电路元件和电路定律231.1 Circuit and Circuit Model24Real circuit elementsIdeal voltage sourceIdeal current sourceIdeal circuit elements理想化理想化抽象化抽象化集总集总3A+-5VIdeal independent source25Ideal load eleme

14、nts (1) resistor(R) (2) capacitor(C) (3) conductor(L)电阻电阻电容电容电感电感26 Ideal coupling elements Dependent source Coupling inductor Ideal transformer+u2* *+u1i1i2N:1VCCS27Course task需需求求 电电路路分分析析 设设 计计 要要 求求 洞洞察察 根根据据分分析析改改进进 根根据据测测量量改改进进 实实验验室室测测量量 实实 际际 电电 路路 电电路路模模型型 概概念念 Analysis basis?Analysis Metho

15、ds?Variables?281. Current and Reference Direction 电流及其参考方向电流及其参考方向Current, i, is the time rate of change of charge past a given point. Unit: ampere, A 1.2 Circuit Variables29v Current is seen as a flow of positive charge. v Current is specified by a value (positive or negative) and a direction (indi

16、cated by an arrow).v Assign reference directions to all the currents arbitrarily. WHY?I1 = 2A(flows in that direction)10V5 I1I1 = - -2A (flows oppositely)10V5 I130 It is difficult to determine the real direction. The real direction is always changing. A B C Z Z Zl Zl Zl A B C + + + - - - UA UB UC Z

17、N 31Example 1：Determine the current I10 1.5A8 10VIExample 2：Point out the actual direction of u and i at t=0.6s,1.8s.+ u5sin(t) V i 3cos(t)mAReference direction is used in circuit analysis, not an actual direction ! I =0.5AThe actual direction is: .322. Voltage and Reference Direction 电压及其参考方向电压及其参考

18、方向Voltage ,( u) is the work required to move a unit positive charge through an element.Unit: volt, V (1 V = 1 J/C)v Voltage is conventionally taken as the potential drop. v 电压的实际方向是电位降低。电压的实际方向是电位降低。+ uab a bU1 = 1V1V5 U1U2 = 1V U2v The direction is indicated by polarity (+,) or an arrow going from

19、a to b.v Voltage uab is a potential difference between a and b. uab = ua ub 332 A-2 Aba+7 V-7 VdcdcReview: Positive versus negativeOnly by a positive or negative value + reference direction can have real meaning.battttdirect currentalternative current (ac)iiidirect current (dc) versus time-varying c

20、urrent2-2itime-varying current34Passive sign convention3. Passive sign convention 关联方向关联方向Non passive sign convention+ UI + UI The current is assumed to enter the assumed positive terminal of an element.对于一元件，其电流参考方向从电压参考方向的对于一元件，其电流参考方向从电压参考方向的“”端流入端流入。Are the following U & I passive convention

21、 or non passive convention? + U= 5VI =-20mA3V10 UI354. Power and EnergyPower, p is the rate of change of energy w.Unit: watt(瓦特，瓦瓦特，瓦), W; 1 W = 1 J/sExample1: u = 5V，i =- -1A, Find the power absorbed by AExample2: u =3V，i =4 4mA, find the power absorbed by B+iup = u i is the power absorbed by the e

22、lement AA+iup = u i is the power supplied by the element BB3V10 UI36Example3: 已知已知U1U410V，U212V，I11A，I2I31.5A。计算各个元件的功率，并验证能量守恒定律。计算各个元件的功率，并验证能量守恒定律。U4+ +- -+ +- -4123U1+ +- -U3+ +- -U2I4I1I2I337Example 4：The electron beam in a TV picture tube caries 1015 electrons per second. As a design engineer,

23、 determine the voltage U0 needed to accelerate the electron beam to achieve 4W.Solution：IQU0I=1.6 10-19 1015 = 1.6 10-4A, U0=p/I=25000V38 Gustav Robert Kirchhoff (1824-1887)，基尔霍夫基尔霍夫, a German physicist, announced his first outstanding research contribution in 1845 concerning the relationship betwee

24、n the current and voltage in an electric network.39An example of a complete circuit to validate KCL and KVL + 25V 6 8 2 8 + 5I I=4A 2.5A 2A 1.5A 2A 0.5A 401.3 Kirchhoffs Laws 基尔霍夫定律基尔霍夫定律1. Concepts of Interconnectionv 支路支路Branch: One or more elements flows the same currentv 节点节点Node: Any point wher

25、e two or more branches are joined. v 回路回路Loop： A closed path .v 网孔网孔Mesh： A loop that does not contain branches within it. 内部不含支路。内部不含支路。5V+ +2A412. Kirchhoffs Current Law (KCL)The algebraic sum of currents entering a node is zero. (current leaving a node is +, entering is -)i1+ i2 i3+ i4= 0 i1i4i2i

26、3 0)(tioutinii Apply KCL to 4 nodes: node a node b . node c node d .i1+ i3= i2+ i4The sum of the currents entering a node is equal to the sum of the currents leaving the node.42 Analogy of water and traffic Think of a node as being similar to an intersection on a roadway. The number of cars entering

27、 the intersection must be equal to the number of cars leaving the intersection or else cars will accumulate in the intersection.One of the fundamental conservation principles in electrical engineering: Physical LawNODENODE43 i2=2t(A) b a c i1=10sint(A) i3=? i3=i2-i1=2t-10sint (A)The algebraic sum of

28、 currents entering a closed boundary is zero.i1+i210(12)=0 i2=1A 47i1= 0 i1= 3A Example:7A4Ai110A- -12Ai2ABiABi2i1ABi3i2i1443. Kirchhoffs Voltage Law (KVL)The algebraic sum of all voltages around a closed path (or loop) is zero.loop 2: .Path a bd c m a: . 0u loop 1: u1u3u40 m 6 2 1 3 4 5 a b c d u1

29、u3 u4 u5 u6 7 u7 risedropuu45A positive charge gains Electrical energy as it moves to a point with higher voltage and releases Electrical energy if it moves to a point with lower voltage. The sum of all the electrical energy changes around any loop must be zero. Physical Law46AB l1l2UAB (沿沿l1)=UAB (

30、沿沿l2）电位的单值性电位的单值性推论推论：电路中任意两点间的电压等于两点间任一条路径上各电路中任意两点间的电压等于两点间任一条路径上各元件电压的代数和。元件电压的代数和。 The voltage between two points is independent of the path linking these two points.32UUUAB 4411UUUUUSSAB I1+US1R1I4_+US4R4I3R3R2I2_U3U1U2U4AB47 图示电路，求电流图示电路，求电流I 和和6V电压源发出的功率。电压源发出的功率。 48求电路中的电压U1、U2和U3。 2V+ + 6V

31、U3+ + U1 + U2 12V+ 491.4 电阻元件电阻元件 Resistors A resistor is a circuit element that dissipates electrical energy (usually as heat). Real-world devices: incandescent light bulb, heating elements (stoves, irons,heaters, etc.), loudspeaker,long wires.RR=tan u/iUnit: , Ohm i u R is the slope of the characteristic and is call resistance.The reciprocal of resistance is conductance. Unit: S, simens,西门子50Ohms Law states that the voltage across a resistor is directly proportional to the current flowing through the resistor. Example 1: u1 =2+4e-3t