PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

Direct Current and Transient Analysis 169

Example 2.21

Assuming that the load is RL, determine the Thevenin’s equivalent circuit of the electri-

cal network shown in Figure 2.66 by

a. Hand calculations.

b. Creating the script fi le Thevenin that simulates Thevenin’s theorem consisting in

varying RL over the range 1 ≤ RL ≤ 50 Ω, in steps of 1 Ω, and computing the respec-

tive powers for each value of RL. Recall that the resistance dissipates maximum

power when RL = RTH and its VTH = 2 VRTH.

FIGURE 2.66

Network of Example 2.21.

Vs = 100 V

−

+

I

RL

RL = 1: 1 : 50

a

a′

R 1 = 20 Ω

R 2 = 60 Ω

FIGURE 2.67

Calculated Thevenin’s equivalent circuit of Example 2.21.

−

+

I

VTH = 75 V RL

a

a′

RTH = 15 Ω

ANALYTICAL Solution

Part a

The VTH and RTH are evaluated by hand.

VTH
 V







60 100

20 60

6000

80

* 75

and

RRRTH





12 

20 60

20 60

1200

80

|| * 15 

The calculated Thevenin’s equivalent circuit, as seen through the terminals aa’, is shown

in Figure 2.67.