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Unformatted text preview: 10/11/10 Dr. Bruce McCann 1 Mesh Current Analysis 1 Mesh Current Circuit Analysis In these lectures, you will learn: How to apply Mesh Current Analysis: • Learn to identify and assign mesh currents. • Learn to write the set of simultaneous algebraic equations. • Learn to express the quantities to calculate in terms of the mesh currents in the circuit. To identify and analyze circuits requiring a “Supermesh” approach. 2 Definitions Branch : a path that connects two nodes. Extraordinary branch : a branch that connects two extraordinary nodes. Loop : any closed connection of branches. Mesh : a loop that does not contain other loops. 3 Example 1 A R3 R1 R2 2 V + - R4 Mesh 1 Mesh 2 Mesh 3 Outer Loop is not a Mesh Why? 4 Mesh Current Analysis How many extraordinary nodes (n e )? 4 How many extraordinary branches (b e )? 6 Number of mesh currents? 3 In general, number mesh currents = b e- (n e-1) In our case, number mesh currents = 6 - (4 - 1) = 3 5 Mesh Current Method Mesh current method provides another systematic tool to solve circuit problems. Only applicable to planar circuits. • Not an issue in EE302. Use mesh currents as the independent variables and write KVL equations around each mesh. 6 10/11/10 Dr. Bruce McCann 2 More on Mesh Current Method Because of the passive sign convention, the direction of the mesh current flow automatically defines the polarity of the branch voltages . Mesh currents are not necessarily the same as branch currents. Mesh currents automatically satisfy KCL since each mesh current both enters and leaves each node it encounters. 7 Mesh Current Analysis Methodology 1. Identify all of the meshes in the circuit. 2. Define the current in each mesh as flowing clockwise. 3. Assign each mesh current a name: (I 1 , I 2 , I 3 ) or (I A , I B , I C ) 4. Using KVL, sum the voltage drops around the mesh and set them = 0. Passive sign convention is used for all voltages, which are determined in relation to the mesh current value In some branches, the current you will use is the difference of two mesh currents. 5. Current sources imply constraints on the mesh currents. More on this later. 8 Example Assume the mesh currents flow clockwise . Apply KVL around the mesh Mesh equation becomes: -V + IR 1 + IR 2 = 0 Same sign convention as KVL approach studied earlier. R 1 R 2 V I 9 A More Complex Example Define two mesh currents I 1 and I 2 . Let’s look at mesh 1. Current in R 1 is I 1 . Sign convention follows I 1 . What is the current in R 3 ? • Net current in R 3 is (I 1- I 2 ). KVL around mesh 1: -V 1 + I 1 R 1 + (I 1-I 2 )R 3 = 0 R 1 R 3 V 1 R 2 V 2 I 1 I 2 10 A More Complex Example Now, let’s look at mesh 2....
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This note was uploaded on 11/01/2010 for the course EE 302 taught by Professor Mccann during the Fall '06 term at University of Texas.
- Fall '06