ENGR338 Lab 2022 Fall
Lab 1 Review of Superposition, Thevenin's Equivalent Circuit, and LTSpice
Mason Brady
Email: mrbrady1@fortlewis.edu

Review of Superposition, Thevenin's Equivalent Circuit, and LTSpice

Introduction: This lab serves mainly to review circuit 1 material including resistance and voltage calculation as well as simplifying circuits using Thevenin's Equivalent Circuit theorum. Everything was checked using LTSpice
specifically using SPICE code which allows us to program the circuit into LTSpice without the need for symbols making it slightly more universal than using the symbols in LTSpice.

Materials: LTSpice

Methods: First, the superposition theory was used to seperate the first circuit into two individual circuits where the voltage drops could be calculated. These voltages were then added together to get the corresponding component values at each point in the circuit, the work can be seen below in Figure 1 of results. Then SPICE code was created for the circuit and the voltages were monitored at each node which allowed me to verify my answers.

For task 2, Thevenin's equivalent circuit thereom was used. Step one of this process is to remove the load, CL. The circuit was then simplified down to a single resistor and voltage source. This was done by first calculating R by finding the total overall resistance of the circuit. Next, V was calculated using our new R value times Vin. This can be seen below in Figure 3. Again, SPICE code was used to verify results.


Figure 1. Hand calculations for task1

Figure 2. SPICE Code for task 1

Task1 Voltage
Figure 3. LTSpice simulation result, Voltages at each node (Green - 1, Blue - 2, Red - 3)

Task1 Current
Fiugre 4.
LTSpice simulation result, Current at each node (Blue -1, Red -2 , Green - 3)

Fiugre 5.
Hand calculations for Task 2

Task2SPICE Code
Figure 6. SPICE Code for task 2

Figure 7. LTSpice verifying time delay of 5.4us until half charge

Discussion: I found this lab extremely difficult. Prior to this lab, I was unable to add parrallel resistors and had no concept of SPICE code. Because of these deficiencies, this lab was a nightmare to complete but with some help and working through the tutorials I was eventually able to complete it and for the most part understand the underlying concepts.