Transistor Introduction

Transistor Introduction and Beginning History

The discovery of the first transistor in 1948 by a team of physicists at the Bell Telephone Laboratories sparked an interest in solid-state research that spread rapidly. The transistor, which began as a simple laboratory oddity, was rapidly developed into a semiconductor device of major importance.

The transistor demonstrated for the first time in history that amplification in solids was possible. Before the transistor, amplification was achieved only with electron tubes. Transistors now perform numerous electronic tasks with new and improved transistor designs being continually put on the market.

In many cases, transistors are more desirable than tubes because they are small, rugged, require no filament power, and operate at low voltages with comparatively high efficiency.

The development of a family of transistors has even made possible the miniaturization of electronic circuits. The illustration shows a sample of the many different types of transistors you may encounter when working with electronic equipment.

Assortment of different transistor types.

Transistors have infiltrated virtually every area of science and industry, from the family car to satellites. Even the military depends heavily on transistors.

The ever increasing uses for transistors have created anurgent need for sound and basic information regarding their operation.

From your study of the diode, you now have the basic knowledge to grasp the principles of transistor operation. In this tutorial you will first become acquainted with the basic types of transistors, their construction, and their theory of operation. You will also find out just how and why transistors amplify.

Once this basic information is understood, transistor terminology, capabilities, limitations, and identification will be discussed. Last, we will talk about transistor maintenance, integrated circuits, circuit boards, and modular circuitry.


The first solid-state device discussed was the two-element semiconductor diode. The next device on our list is even more unique. It not only has one more element than the diode but it can amplify as well.

Semiconductor devices that have-three or more elements are called TRANSISTORS. The term transistor was derived from the words TRANSfer and resISTOR. This term was adopted because it best describes the operation of the transistor - the transfer of an input signal current from a low-resistance circuit to a high-resistance circuit.

Basically, the transistor is a solid-state device that amplifies by controlling the flow of current carriers through its semiconductor materials.

There are many different types of transistors, but their basic theory of operation is all the same. As a matter of fact, the theory we will be using to explain the operation of a transistor is the same theory used earlier with the diode except that now instead of just two junctions there are now three elements that make up the transistor.

The three elements of the two-junction transistor are (1) the EMITTER, which gives off, or emits," current carriers (electrons or holes); (2) the BASE, which controls the flow of current carriers; and (3) the COLLECTOR, which collects the current carriers.

Below is a short video tutorial on the basic function of a transistor.

We will cover the construction, applications, and function of the transistor in subsequent tutorials.

Transistor Classifications

Transistor construction

Transistor-Theory, the NPN forward biased transistor and the NPN forward biased transistor junction.

Reverse-bias junction in the NPN transistor and the NPN interaction.

The-PNP-Transistor and the PNP forward biased junction.

The PNP Reverse Bias Junction

The Basic Transistor Amplifier

Types of Bias

Transistor-configurations and the common emitter

The Common Base Transistor

The Common Collector transistor configuration

Transistor maintenance, specifications, and identification

Testing transistors

Transistor lead identification

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