Lecture 8 Review: Mesh Analysis Related educational materials: Nodal analysis Supernodes Additional nodal analysis examples Mesh Analysis Related educational materials: Chapter 3.2, 3.3

Review: Nodal Analysis Choose reference node Identify independent nodes Label “constrained” voltages Apply KCL at independent nodes Write the KCL equations in terms of node voltages Solve equations to determine the node voltages Determine desired circuit parameters from node voltages

Supernodes In example 3 of lecture 7, we applied KCL at a supernode

Supernodes – continued Example: A node is defined as having a single, unique voltage We can, however, apply KCL at supernodes which contain multiple nodes

Supernodes in nodal analysis Supernodes are especially useful in nodal analysis when dependent nodes (voltage sources) are present Define a supernode containing the dependent nodes The supernode contains the voltage source and the nodes to which it is connected Apply KCL at the supernode

Supernodes are useful, but not required Supernodes are not essential for nodal analysis, as long as you account for all currents Need to explicitly include currents through voltage sources Lecture 7, Example 3:

Lecture 7, Example 3 – alternate approach

Example 1 Determine the voltage across the 6 resistor

Example 1 – alternate approach

Example 2 Use nodal analysis to write a set of equations from which you can determine the current through the 6 resistor.

Mesh analysis – review Identify mesh loops The currents around these loops are the mesh currents Use Ohm’s Law to write KVL around each loop in terms of the mesh currents Solve these equations to determine the mesh currents Any desired circuit parameter can be determined from the mesh currents

Nodal and mesh analysis – comparison Nodal analysis: Define independent nodes Apply KCL at independent nodes Use Ohm’s Law to write KCL in terms of node voltages Mesh analysis: Define “mesh loops” Apply KVL around the mesh loops Use Ohm’s Law to write KVL in terms of mesh currents

Mesh Analysis We will illustrate the mesh analysis technique in the context of an example circuit:

Mesh Analysis Step 1: Choose mesh loops and identify mesh currents Kill sources (short voltage sources, open-circuit current sources) Recommendation: mesh loops should not have other loops in their interior

Mesh Analysis Step 2: Replace sources and write constrained loops Constrained loops go through current sources Constrained loops are somewhat arbitrary, but their direction and magnitude must be consistent with the source through which they pass

Mesh Analysis Step 3: Apply KVL around the mesh loops Use Ohm’s Law to write voltage drops in terms of mesh currents Voltage polarities in KVL must be consistent with that loop’s mesh current

Mesh Analysis Step 3: continued

Mesh Analysis Step 4: Solve the equations for mesh currents Use mesh currents to determine the circuit parameters of interest Note: The total current in an element is the sum of the mesh currents in the element