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Chap. 2 Circuit Elements

Chap. 2 Circuit Elements. C ontents. 2.1 Voltage and Current Sources 2.2 Electrical Resistance (Ohm’s Law) 2.3 Construction of a Circuit Model 2.4 Kirchhoff’s Laws 2.5 Analysis of a Circuit Containing Dependent Sources. Objectives. 1. 了解 理想的基本電路元件的符號與特性 ：獨立電壓與

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Chap. 2 Circuit Elements

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  1. Chap.2Circuit Elements Contents 2.1 Voltage and Current Sources 2.2 Electrical Resistance (Ohm’s Law) 2.3 Construction of a Circuit Model 2.4 Kirchhoff’s Laws 2.5 Analysis of a Circuit Containing Dependent Sources Objectives 1. 了解理想的基本電路元件的符號與特性：獨立電壓與 電流源、相依電壓與電流源、電阻器。 2. 了解歐姆定律、克希荷夫電流定律、克希荷夫電壓 定律，並利用此三種定律來分析簡易電路。 3. 了解如何計算簡易電路中各元件的功率，並且能夠判 斷整個電路是否保持功率守恆。

  2. 2.1 Voltage and Current Sources • 電源(electrical source) ： • 可將非電能轉為電能或將電能轉為非電能的一種裝置。 • 具有提供功率或是吸收功率的特質。 • 通常將理想電壓源及理想電流源當成電路的基本元件。 理想電壓源(ideal voltage source) : 不論流過其端點之電流大小為何，而其兩端電壓維持在規定值的電路元件。 理想電流源(ideal current source) : 不論兩端電壓多大，在其兩端內之電流維持在規定值的電路元件。 獨立電源(independent source) : 會依規定供給電路電壓或電流值，不需仰賴電路中的其他電壓或電流。 獨立電壓源 獨立電流源

  3. 2.1 Contd. 相依電源(dependent source)或 受控電源(controlled sources): 所提供給電路的電壓或電流值，需仰賴電路中的其他電壓或電流。 • 1. 相依電源通常用菱形符號來表示 • 電壓源以極性+-標示，電流源以方向標示。 • 因受電路中其他電壓或電流所控制，共有四種組合，如右圖所示。 VCVS VCCS 主動元件(active element) : 能產生電能的裝置，如電源。 被動元件(passive element) : 不能產生電能的裝置，如電阻器、電感器及電容器。 CCVS CCCS 相依電壓源 相依電流源

  4. EX 2.1 Testing Interconnections of Ideal Sources Connection (a) is valid. Connection (b) is valid. Connection (c) is not permissible. Connection (d) is not permissible. Connection (e) is valid.

  5. EX 2.2 Testing Interconnections of Ideal Independent & Dependent Sources Connection (a) is invalid. Connection (b) is valid. Connection (c) is valid. Connection (d) is invalid.

  6. Assessing Objective 2.2 a) What value of vgis required inorder for the interconnection to bevalid? b) For this value of vg, find the powerassociated with the 8 A source. ANSWER: (a) −2 V; (b) −16 W (16 W delivered).

  7. 電導(conductance): 電阻的倒數，以G表示，單位為S，以往以姆歐為單位( )。  2.2 Electrical Resistance (Ohm’s Law) 電阻(resistance) : 阻礙電流流動的物質特性，以R表示，單位為 。 電阻器(resistor): 具電阻特性之電路元件。 電阻器 理想電阻器的電阻值不隨時間改變，而實際電阻器則會隨時間改變； 若在分析電路時，實際元件偏離值不多時，都可用理想電阻器取代。 Ohm’s Law (歐姆定律) Passive Sign Convention! Power in a Resistor

  8. EX 2.3 Calculating Voltage, Current, and Power

  9. Short circuit Open circuit Switch 2.3 Construction of a Circuit Model EX 2.4 Constructing a Circuit Model of a Flashlight

  10. EX 2.5 Construction of a Circuit Model Based on Terminal Measurements

  11. 2.4 Kirchhoff’s Laws 端點(terminal): 電路元件的兩端; 節點(node): 二個以上電路元件相連的地方 Kirchhoff’s Current Law (KCL) The algebraic sum of all the currents at any node in a circuit equals zero. (電路中任一節點其所有電流代數和為零) 電流需有代表方向的代數符號，若將流出節點的電流定為正號，那麼流入節點就是負號。

  12. 2.4 Contd. (KVL) 封閉路徑或迴路(closed path or loop) : 指從某一節點開始，沿著選定的電路元件回到起點，且其間之節點只許經過一次。 Kirchhoff’s Voltage Law (KVL) The algebraic sum of all the voltages around any closed path or loop in a circuit equals zero. (電路中任一封閉路徑或迴路其所有電壓代數和為零) 若電壓下降為正號，那麼電壓上升就為負號； 若電壓下降為負號，那麼電壓上升就為正號。

  13. EX 2.6 Using KCL

  14. EX 2.7 Using KVL

  15. EX 2.8Applying Ohm’s Law and Kirchhoff’s Laws (KCL) (KVL & Ohm’s law) Also, (power supplied = power absorbed) Power Balanced

  16. EX 2.9Constructing a Circuit Model Based on Terminal Measurements

  17. 2.5 Analysis of a Circuit Containing Dependent Sources ◆ Once we know io, we can calculate vousing Ohm’s law. ◆ Once we know i, we also know the current ofthe dependent source 5i. ◆ The current in the 500 V source is i. (KVL & Ohm’s law) (KCL)

  18. EX 2.10Applying Ohm’s Law and Kirchhoff’s Laws • 2 loops, 2 unknowns io & iS (vo = 3 io) (KVL & Ohm’s law) (KVL & Ohm’s law) Check! OK!

  19. EX 2.11An Amplifier Circuit Amplifier (Controlling variable) (KCL) (KVL & Ohm’s law)

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