Fall 2001 ENGR-201 Example 4.8 1

Example 4.10 Irwin, Page 127Find the Thevenin equivalent circuit at points A-B for the circuit shown.

We need to find two quantities: VTH = Voc and RTH = Voc/ISC

If we use nodal analysis and/or mesh analysis or any other appropriate techniques, we find VTH = 0V and ISC = 0A (because there are no independent sources of power in the circuit)

RTH = Voc / ISC = 0V/0A = ?????

VTH = 0V is equivalent to a short circuit

ISC = 0A is equivalent to an open circuit The Thevenin (Norton) equivalent consists of a single resistor.

Fall 2001 ENGR-201 Example 4.8 2

Example 4.10 – Find RTH

To make our work easier, we will find RTH to the at points C-D first.

THS

1VR =

I

To find RTH apply a known voltage source (1V) and determine the amount of current demanded. .

Fall 2001 ENGR-201 Example 4.8 3

Example 4.10 – Find RTH at C-D

X

X X

S X

TH

1VI = 1mA

1kV =2000I =2V

1V-2VI =I + 1mA-0.5mA =0.5mA

2k1V

R 2k0.5mAC D

We can now replace the circuit to the left of points C-D with its Thevenin equivalent.

Fall 2001 ENGR-201 Example 4.8 4

Example 4.10 – Find RTH

The Thevenin (and Norton) equivalent circuit, then, is

TH A-B

TH A-B

R =2k || 3k 2k

R 1.43k