Lab 5 - Thevenin Equivalents

Objective:
To understand and determine the Thevenin Equivalence within a given circuit

Original Circuit Schematic

The schematic above is the circuit that is used for the lab.  The purpose is to determine the Thevenin Voltage and Resistance for the component labeled RL2.

Pre-Lab Calculations:

Before starting the experiment, the values of RTH and VTH are first calculated using the below two schematics.

Given:

RC1 = 100Ω

RC2 = RC3 = 39Ω

RL1 = 680Ω

VS1 = VS2 = 9V

Calculation for node Vx(VTH) needed for RTH

Calculation for RTH 

Thevenin Equivalent Circuit Schematic

Calculation for smallest permissible RL2, Short-circuit current, and Open-circuit voltage

The calculated values:

RTH = 65.96 Ω

VTH = 8.64337 V

RL2 = 820 Ω

ISC = 0.131068 A

VOC = 8.64 V

The Experiment Model:

Thevenin Equivalent Circuit Schematic:

Config:  RL2 = RL2,min

Config: RL2 = ∞ Ω

Component Measurements

Results for Configurations 

The percent error obtained is pretty small meaning that the results can be assumed to be fairly accurate.  This shows that the Thevenin Equivalent Circuit can be used to determine the values of the variable resistor.

Original Circuit Schematic:

Config:  RL2 = RL2,min

Config: RL2 = ∞ Ω

Component Measurements

Results for Configuration

The percent error obtained is fairly small, which allows for the assumption that the data is accurate.  Since the values are similar to the Thevenin Equivalent Circuit, it can be seen that the Thevenin equivalent components are the same as the variable components of the original circuit. 

Maximum Power Effect:

The results show that when RL2 = RTH is when the maximum power is achieved and when RTH is smaller or larger, it does not produce a larger wattage.