Thevenin and Norton Equivalent Circuits

Jack Ou

Department of Electrical and Computer Engineering

Sec. 5.4-Sec. 5.5

Basic Idea

Note that voc = iscRt .

Open Circuit Voltage (voc)

1. Remove the load

2. Determine the open circuit voltage

Example

Determine voc .

Short Circuit Current

1. Remove the load

2. Short a and b

3. Calculate isc

Example

Determine isc .

Thevenin Resistance

Steps:

1. Replace all independent voltage sources with shorts

2. Replace all independent current sources with opens

3. Two possibilitiesI Only resistors are left: find the Thevenin resistance by merging

the resistors.I Else, apply either a test voltage or a test current to find the

Thevenin resistance.

Note: In step 1 and 2, dependent current and voltage sources arenot replaced with open circuits or short circuits.

Example 1

Example 2: Find Rt by Merging Resistors

Example 3: Use a test source to find Rt