enee204Lectures_03_04_modified

enee204Lectures_03_04_modified - Welcome to ENEE 204 Basic...

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1 9/6/2005 1 Welcome to ENEE 204 Welcome to ENEE 204 Basic Circuit Theory Basic Circuit Theory Lecture 3 Lecture 3 TOPICS: 9/6/2005 2 Formulas of the Instantaneous Power Consumption of Various Devices Resistor: iR v = ) ( ) ( ) ( t i t v t p = R v R p 2 2 i = = Capacitor: dt dv C i = = = 2 2 Cv dt d dt dv v C p Always positive: always consumes energy If power > 0 : absorbs energy If power < 0 : gives energy Inductor: dt di L v = = = 2 2 Li dt d dt di i L p If power > 0 : absorbs energy If power < 0 : gives energy
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2 9/6/2005 3 Circuit Analysis Circuit Analysis Goal: to figure out the CURRENTS, I’s and VOLTAGES, V’s in ALL circuit elements. v s =20V i s R 2 =5 i 2 , v 2 i 1 , v 1 R 1 =5 i A =2 A 9/6/2005 4 CHAPTER 2: KCL and KVL CHAPTER 2: KCL and KVL Rules to obtain the voltages and currents in all parts of the circuit I S I 1,, v 1 I 3,, v 3 I 2,, v 2 I 4,, v 4 I 5,, v 5 I 6,, v 6 I 7,, v 7 I 8,, v 8 i k : current through element, k v k : voltage acrosss element, k
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3 9/6/2005 5 Terms Used in Analyzing Circuits Terms Used in Analyzing Circuits 1. Branch – any line with one 2-terminal device 2. Node - point at which branches meet ( ) (a point where two or more elements are connected together) trivial node: only two elements are connected non-trivial node: more than two are joined 3. Loop - set of branches that form a closed path ( ) 4. Mesh - the simplest type of loop ( no element is inside the loop) trivial mesh: contains only 2 elements non-trivial mesh: more than 2 elements 9/6/2005 6 A loop loop is a set of branches that form a closed path. Here are some example loops Each node is encountered only once as the loop is traced.
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4 9/6/2005 7 A mesh mesh is the simplest type of loop loop . * Meshes do not enclose any branches Here are some examples of non-trivial meshes. Here is an example of a trivial mesh. * For a planar circuits only 9/6/2005 8 Example: Identifying nodes and neshes Branches: 14 NODES: Non-trivial (6) and trivial nodes (3) Note: BE CAREFUL OF OVER COUNTING NODES! (connecting lines are assumed to have no resistances) NOT NODES ! MESHES: Non-trivial (4) and trivial meshes (2)
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5 9/6/2005 9 Kirchhoff’s Kirchhoff’s Current Law (KCL) Current Law (KCL) Kirchhoff's Kirchhoff's Voltage Law (KVL) Voltage Law (KVL) i 1 (t) i 2 (t) i 3 (t) i 4 (t) i 5 (t) i k (t) = 0 k KCL: The algebraic algebraic sum of electric currents at any node is equal to zero at every instant of time. + sign: current is going into the node - sign: current is going out of the node 0 5 4 3 2 1 = + i i i i i KVL: The algebraic sum of the voltages at any loop is equal to zero at every instant of time. v 2 (t) v s (t) Loop trace v 6 (t) v 1 (t) v 3 (t) v k (t) = 0 k + sign: tracing direction is going into the + terminal -sign: tracing direction is going into the – terminal Signs of terminal are determined by REF. DIRECTIONS . 0
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enee204Lectures_03_04_modified - Welcome to ENEE 204 Basic...

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