PHYS345 PHYS345 Class 5

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Source Substitution

Review of Mesh and Nodal Analysis

Thevenin's Theorem

Thevenin generator Any two-terminal linear circuit can be replaced with a voltage source in series with a resistance which will produce the same effects at the terminals.

VTh is the open-circuit voltage Voc between the two terminals of the circuit that the Thevenin generator is replacing.

RTh is the ratio of Voc to the short-circuit current Isc.
In linear circuits, this is equivalent to "killing" the sources and evaluating the resistance between the terminals. Voltage sources are killed by shorting them; current sources are killed by opening them.

Detailed Example of Thevenin Approach

      Concept Check: Thevenin's Theorem

Norton's Theorem

Norton generator Any two-terminal linear circuit can be replaced with a current source in parallel with a resistance which will produce the same effects at the terminals.

IN is the short-circuit current Isc of the circuit that the Norton generator is replacing.

Again, RN is the ratio of Voc to the short-circuit current Isc.
Note that for a given circuit, RN = RTh.

Detailed Example of Norton Approach

      Concept Check: Norton's Theorem


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Last updated Sept. 15, 1998.
Copyright George Watson, Univ. of Delaware, 1998.