Thevenin Equivalents Lab

In this experiment we studied a complex circuit which was transformed into a Thevenin equivalent circuit. Given the fact that the following circuit is linear,

we can simplify it to its Thevenin equivalent,

to find values of Resistance in R2, as well as the voltage and current flow through Load 2.

Problem:

We can start analyzing the circuit by obtaining Thevenin Resistance, Rth. In order to do so, the voltage sources must be turned off:

• Step 1A:

Use nodal analysis to obtain Vx or Vopen circuit by opening the circuit and disregarding RL2:

• Step 1B:

Next we use nodal analysis again to get the voltage Vy when short-circuiting the current:

• Step 1C:

If we look at the Thevenin equivalent circuit, we can determine:

1. Smallest permissible RL2 with voltage division technique
2. Short circuit current (Isc) through Ohm's Law (found above already)
3. Open-circuit voltage by inspection

Step 2: Lab equipment 
Stage 1: Build Thevenin equivalent circuit on breadboard

• Variable resistance boxes for Rth and RL2
• Power supply channel V1 set to Vth
• RL2 = RL2min and measure VLoad2
• Replace RL2 by open circuit and measure VLoad2

Thevenin Circuit Equivalent

Stage 2: Build original circuit on breadboard

• Variable reisistance box for RL2 and fixed resistors for Rc1, Rc2, Rc3, RL1
• Power supply channels V1 and V2 to implement Vs1 and Vs2
• RL2 = RL2min and measure VLoad2
• Replace RL2 by open circuit and measure VLoad2

Original circuit with fixed resistors

Step 3A: Measuring components before assembly of circuit

Component	Nominal Value	Measured Value	Power/Current Rating
Rth	66 ohms	65.9+/-0.1 ohms	1 W
RL2min	819.9 ohms	820 +/-0.1 ohms	1 W
Vth	8.64 V	8.66+/-0.1 V	10 mA

Step 4A: Thevenin Equivalent Circuit

RL2 = Infinite resistance (absence of black variable resistance box)

Step 5A: Performing the experiment

Config	Theoretical Value	Measured Value	Percent Error
RL2 = RL2min	Vload2 = 8V	7.77+/-.01	2.88%
RL2 = Infinite R	Vload2 = 8.64V	8.70+/-.01	0.69%

Step 3B: Measure components of original circuit before assembly

Component	Nominal Value	Measured Value	Power/Current Rating
Rc1	100 ohms	98+/-.1 ohms	1/8 W
Rc2	39 ohms	38+/-.1 ohms	1/8 W
Rc3	39 ohms	39+/-.1 ohms	1/8 W
RL1	680 ohms	667 +/-1 ohm	1 W
Vs1	9 V	9.10+/-.01 V	10 mA
Vs2	9 V	9.18+/-.1 V	11 mA

Step 4B: Building Original Circuit on breadboard

Step 5B: Performing the experiment

Config	Theoretical Value	Measured Value	Percent Error
RL2 = RL2min	Vload2 = 8V	6.90+/-.01	13.75%
RL2 = Infinite R	Vload2 = 8.64V	7.94+/-.01	8.10%