Introductory Electrical Engineering With Math Explained in Accessible Language

29Transistor Amplifiers: The Magic Component

29.1 Introduction

In this chapter, we will examine the usage of transistors as amplifiers.

We will show how transistors are able to “amplify”¹ signals and will briefly introduce the reader to how they work.

29.2 Transistor as Amplifiers

Nothing is farther from the truth than thinking transistors are magical devices that can amplify the signals they receive, like a magical portal that receives the signal and amplifies it.

In fact, transistors are like switches that can manipulate and modulate the voltage coming from the power supply to generate a huge copy of the input signal, creating the illusion of amplification.

The output signal is not the input signal amplified but rather the power supply voltage modulated to look like the input signal.

29.3 The Water Storage Tank

Imagine a huge water store tank with a large output pipe. At the bottom of the tank, a tiny water valve is connected electronically to a huge water valve that opens or closes the main pipe. Therefore, if you rotate this tiny valve to one direction, it will make the huge water valve open and let a gigantic amount of water exit from the tank. If you rotate the tiny water valve to the other direction, the huge valve will close.

Thus, small rotations of the tiny valve will produce huge rotations of the largest valve.

This can be interpreted as an amplification: a small rotation producing a large rotation.

This is what roughly happens with transistors: a tiny current ...