Introductory Electrical Engineering With Math Explained in Accessible Language

21Thévenin’s Theorem: Circuit Analysis

21.1 Introduction

In this chapter, we will examine the Thévenin’s theorem, also known as equivalent circuit theorem, created by Léon Charles Thévenin, a French telegraph engineer who extended Ohm's law to the analysis of complex electrical circuits.

This theorem makes it possible to convert complex circuits into simpler ones that are electrically equivalent and behave in the same way.

21.2 The Theorem

Unlike the source transformation theorem, which aims to replace parts of circuits to convert everything into a voltage or current source with resistors, the Thévenin Theorem's objective is to replace the whole circuit with a voltage source in series with a resistor.

Figure 21.1 shows the goal of the Thévenin's theorem to replace a complete circuit with a voltage source, called the equivalent Thévenin voltage source, or V_Th in series with a resistor, called the equivalent Thévenin resistor, or R_Th.

Figure 21.1 Thévenin equivalent circuit.

21.2.1 The Equivalent Thévenin Circuit

The Thévenin circuit always represents the equivalent seen through two terminals of the original circuit that can be the input, the output, or any other points.

Figure 21.2 shows a black box representing a circuit and points A and B representing the input.

Figure ...