We explain what a transistor is, how it is composed and its various functions. Also, its general characteristics, classification and more.

What are Transistors?

Transistors are semiconductor electronic devices , responsible for transmitting an outgoing signal (output) in the presence of an incoming (input), as part of an electronic circuit of some kind. The term "transistor" comes from the English transfer resistor ( transfer resistor ), and initially they were designed to modulate electrical current .

Transistors, in this sense, fulfill functions of amplification, oscillation, switching or rectification of the electrical signal within the given circuit, and are used in a large part of the integrated circuits of contemporary electronic devices.

The first operational transistors were developed in 1955 , despite the fact that their composition had been studied since practically the beginning of the century, in search of methods to improve electrical and electronic conduction. The working principle of transistors (the so-called “transistor effect”) was discovered by the Americans John Bardeen, William Shockley and Walter Houser Brattain in 1948 and earned them the Nobel Prize in Physics in 1956.

Transistor components

Transistor components

Transistors are essentially made up of three pins or cables, each one in charge of a different task and which are called:

  • Transmitter. From where the electrical flow enters the encapsulated interior of the transistor.
  • Base. The one that modulates the flow between emitter and collector.
  • Manifold. Where the current flows once it has been modulated by the base.

Operation of transistors

Transistors operate as tolls or alcabalas in the electrical flow , allowing to increase, decrease or modulate its intensity according to three possible positions within a circuit:

  • In active. It allows the passage of more or less current (modulated) towards the collector and, therefore, back to the circuit.
  • Sectional. It prevents the passage of all the current.
  • In saturation. It allows the full passage of the current.

Transistor functions

Transistor functions

The functions of a transistor as part of an electrical circuit can be two fundamentally:

  • As a switch. It cuts off the electrical flow from a small command signal.
  • As an amplifier. It receives a small electrical signal that, as it exits the transistor, will have become a larger one.

However, transistors can also act as an oscillator, switch or rectifier, which allows the electrical flow in the circuit to be conducted in the desired way .

Materials of a transistor

Transistors are made by taking advantage of the semiconductivity of certain materials , such as germanium (Ge) or gallium arsenide (GaAs). At present, the preferred material for this is silicon (Si) , a metalloid abundant in the earth's crust.

Binary code

Binary code

Transistors have a lot to do with the development of computational binary code (composed of ones and zeros), since each number indicates a position of the switch transistor : active or inactive, allowing electricity to pass or not: 0 = no current; 1 = with current.

Using a transistor

In contemporary appliances, equipped with complex integrated circuits, transistors abound by the thousands. From clocks, televisions , radios , computers, cell phones , tomographs, music players and even fluorescent lamps are possible thanks to this electric drive technology .

Types of transistors

Types of transistors

There are several types of transistor, depending on their manufacture and their capabilities:

  • Point contact transistor. The first type of transistor invented and capable of making gain, despite the fact that it was fragile and difficult to manufacture. It consisted of two metal tips on a germanium base, based on surface effects. Today it has disappeared.
  • Bipolar junction transistor. It is manufactured on a base of semiconductor material (intermediate between conductor and insulator) commonly silicon, on which a crystal substrate is located that is polarized through electron donor elements, such as arsenic or phosphorus. These poles constitute the emitter and the collector.
  • Field effect transistor. It consists of a bar of semiconductor material around which an electric field is generated, in order to control the flow of energy through a single pole (that is why they are called unipolar).
  • Phototransistor. They operate like normal transistors, but being sensitive to electromagnetic radiation close to visible light , they can be operated through an illumination mode: when light acts as base current.

Advantages of transistors

The use of transistors represented a leap forward with respect to the usual electrical handling techniques , consisting of thermionic valves. Not only because it allowed to maximize the potential of the devices in sizes much smaller than the initial ones, but it also facilitated the construction of devices capable of withstanding much more voltage, allowing their use in conditions of high electrical power.

Furthermore, transistors are relatively inexpensive, consume little power , provide many hours of use, and can remain in storage for a long time without breaking down.



IGBTs are advanced models of transistors that, grouped around a common circuit, can amplify electrical currents from 1000 amperes to voltages of several thousand volts, thus allowing control of the power of various electronic devices, including the motors of the modern automobiles and medical defibrillators, used for the resuscitation of recently deceased patients.

Transistor activity

Unlike other elements that intervene in electronic circuits, such as resistors, capacitors and inductors, which play a passive role in them, transistors are assigned an active role within the circuit , since they not only ensure stability and preservation of it, but are part of its functional structure

The above content published at Collaborative Research Group is for informational and educational purposes only and has been developed by referring reliable sources and recommendations from technology experts. We do not have any contact with official entities nor do we intend to replace the information that they emit.


Abubakr Conner brings a diverse skill set to our team, and covers everything from analysis to the culture of food and drink. He Believes: "Education is the most powerful weapon that exists to change the world." .

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