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ECE 3144 Lecture 8

ECE 3144 Lecture 8. Dr. Rose Q. Hu Electrical and Computer Engineering Department Mississippi State University. a. a. R a. R 1. R 2. R c. R 3. R b. b. c. c. b. Reminder for Lecture 7. Wye-Delta or Delta-Wye transformation Circuits with dependent sources

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ECE 3144 Lecture 8

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  1. ECE 3144 Lecture 8 Dr. Rose Q. Hu Electrical and Computer Engineering Department Mississippi State University

  2. a a Ra R1 R2 Rc R3 Rb b c c b Reminder for Lecture 7 • Wye-Delta or Delta-Wye transformation • Circuits with dependent sources • treat the dependent source as though it were an independent source. • write the equations that specifies the relationship of the dependent source to the controlling

  3. Problem solving strategy: Delta-Wye transform (HW 2.73)

  4. Problem solving strategy: Delta-Wye transform • if possible, simplify the circuits first by using series-parallel combination techniques • Repeat step 1 until no series or parallel combination existing in the network. • Re-draw the shape of the circuit to the one you are more familiar with if necessary • Identify the Delta shape components or Wye shape components in the simplified circuit. • Determine where and how to do Wye-Delta or Delta-to-Wye transforms. • Perform Wye-to-Delta (or Delta-to-Wye) transformations so that the circuit seen is represented as a series-parallel interconnection of resistors.

  5. It’s your turn: how to solve the problem? HW 2.72: Given the network, find I I • First if there are resistors in series or in parallel in the circuit network given? • If there are, how to do the simplification; • If there are not, do you feel comfortable or familiar with the shape of the circuit given? • If not, redraw the circuit network. • Identify the Delta-shape or the Wye-shape which you can do the transformations.

  6. Problem solving strategy: Circuit with dependent sources (HW Problem 2.85 in the textbook: for the network shown, choose the values of and such that is maximized. What is the resulting ratio , Vo /Vs ? (voltage divider for resistors in series) (voltage divider for resistors in series)

  7. Problem solving strategy: HW 2.69

  8. Summary for Chapter 2 • Resistor, Resistance, Resistivity • Ohms’law V = I*R: only linear resistors satisfy Ohm’s law. • Power P = V*I= V2/R = I2R • Kirchoff’s current law (KCL): The algebraic sum of the currents leaving (entering) a node is zero. • Kirchoff’s voltage law: The algebraic sum of the voltages around any loop path is zero. • Single loop circuit: resistors in series and voltage divider • Single node circuit: resistors in parallel and current divider • Circuits containing a single source and a series-parallel interconnection of resistors • Wye-delta or Delta-to-Wye transformations • Circuits containing dependent sources

  9. Exam 1: Feb 6 • Exam 1 covers Chapter 1 and Chapter 2. • Chapter 1: Basic concepts • Charge (q), current (i), and their relationship • Voltage (v), work/energy (w), power (p), and their relationships. • Passive sign convention • The positive reference of voltage v(t) is at the same terminal the the current variable i(t) is entering. • How to determine absorbing or supplying energy? • Active elements and passive elements • Active elements • Independent sources • Dependent sources. • Chapter 2: See slide 7

  10. Homework for Lecture 8 • Problems 2.79,2.80, 2.81, 2.83, 2.87

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