Download Tutorial 4: Network Theorems

ECE 240 – Electrical Engineering Fundamentals
PSPICE Tutorial 4
Network Theorems
The examples in this tutorial and the corresponding homework continue to deal with the DC
analysis of circuits, or DC Bias analysis in PSPICE. The focus of this tutorial is to illustrate the
use of PSPICE to verify Norton and Thevenin’s Theorem and the Maximum Transfer of Power
Theorem.
Norton and Thevenin’s Theorem
In class, the Thevenin and Norton equivalents of the circuit to the left of a-b shown in figure 1
were found. These equivalent circuits are shown in figures 2 and 3.
4A
a
61
i
41
24 V
+
-
21
31
b
Figure 1. Complete Circuit
61
24 V
+
-
Figure 2. Thevenin Equivalent
4A
61
Figure 3. Norton Equivalent
By Norton and Thevenin’s Theorems we know that adding the 2 Ω resistor to either of these
equivalent circuits will result in the same current flow, i. This can be verified by simulating the
three circuits in PSPICE and showing that the currents obtained in all three circuits are the same.
Figure 4 show the results of the PSPICE simulation. Note that the current in all three circuits is
3A.
Figure 4. PSPICE Simulation of Norton and Thevenin Equivalent Circuits
Maximum Transfer of Power
In class the maximum transfer of power theorem was used to find the value of R in the circuit
shown in figure 5 that would result in the maximum transfer of power to R.
V1
41
-+
41
41
+
100 V
+
-
V1
41
-
+
-
20V
Figure 5. Maximum Transfer of Power Circuit
R
It was determined that the value of R = 3Ω would result in the maximum transfer of power. This
result can be verified in PSPICE as follows.
1. Use PSPICE to simulate the circuit with a resistance of R = 3Ω. Display the power
delivered to the 3 Ω resistor. Figure 6 shows that 1.2KW are delivered to this 3Ω
resistor.
Figure 6. Simulation of Circuit with R = 3Ω
2. Repeat this simulation with R = 2.5 Ω. As shown in figure 7, the power to the resistor
has dropped to 1.19 KW.
Figure 7. Simulation of Circuit with R = 2.5Ω
3. Repeat step 2 for R = 3.5 Ω. Again the results shown in figure 8 confirm that the power
has dropped.
Figure 8. Simulation of Circuit with R = 3.5Ω