How does a transistor work and what is its application?

The transistor appeared in order to replace the old electronic valves, which served to regulate the flow of electrons. Thus, the discovery of transistors made it possible to create the most diverse advanced devices that we currently have, such as video games, cell phones, computers and other infinity of electronic equipment. The discovery of transistors changed the way of life in our modern society and the electrical we know. So important is this device that we will show what a transistor is, the types of transistors, the applications for the transistors and the main characteristics of the transistors.

What is a transistor?

In a simple way, transistors are considered as a kind of switch. That’s right, in its most basic configuration the transistor operates as a switch, but it can work in several ways, which will depend on its configuration. These devices are extremely important for electronics, we can highlight the two main and best-known types of signal transistors NPN and PNP.

PNP transistors are those that operate with positive – negative – positive values, they are transistors that carry a positive signal at the output, that is, the transistor is fed with a positive and negative voltage signal for the operation of the internal circuit, and at the output, it emits a positive sign. NPN transistors – Negative – Positive -Negative – works similar to PNP but has a negative sign on its output, there are hundreds of working voltages and applications for transistors, but most of them work in NPN mode.

Symbols of the NPN transistor and PNP transistor.

Transistors are manufactured in different ways, but most of them are manufactured with three different terminals or “legs”, which are:

  • B = Base, main responsible for the activation of the transistor.
  • C = Collector, positive terminal of the transistor.
  • E = Emitter, Negative terminal of the transistor.

The basic principle of operation of a transistor, when it is activated through the supply voltage, is to allow a current to pass through a resistor at its base, in this way the next component of the circuit is fed. For this to happen, the transistor must necessarily receive a voltage at its base, the aforementioned resistor is present to protect the transistor from current and surge voltages.

Transistors are used in electronic circuits and are often used as amplifiers for a voltage signal. There are several types of transistors, each of them varies in application and work characteristics, some are used as a simple switch or amplifier for example.

We can also use the transistor in parallel with the loads that demand a high electrical current, preventing this current from traveling through more sensitive electronic components. In addition there are light sensitive transistors, called photo transistors, they are used in public lighting circuits, making the connection of the luminaires only at night, for example.

Field effect transistor:

The field effect transistor consists of three terminals, a port, a source and a drain. This transistor is controlled by the electrical voltage, this voltage when placed on the door causes an electrical current to flow from the source to the drain of the transistor. This transistor can also be found in NPN or PNP mode.

Field effect transistors have a very high input impedance, since this high input impedance means that they have very little current flowing through them. Thus, these types of transistors seek little current from the power supply in a circuit. This is ideal because they do not disturb the power elements of the original circuit to which they are connected.

Bipolar Junction Transistor:

The bipolar junction transistor (TBJ) has in its constructive form three terminals, being the base, the collector and the emitter. Unlike field effect transistors, TBJs are devices controlled by electrical current, that is, a small current at the base causes a much greater current flow in the emitter. As well as the field effect transistor, bipolar junction transistors in the NPN or PNP type can also be found.

These transistors are the only ones that are activated by the current input in their base. The low impedance (or resistance) allows current to flow through the base of the transistor. Due to this low impedance, these transistors also have the highest amplification of all. Their disadvantage is having low input impedance, and being able to draw significant current from a circuit, thus disturbing the power supply.

Small signal transistors:

Small signal transistors are transistors used primarily to amplify low-level signals, but they can also work well as switches. The small transistors can amplify the input signals. Typical hFE (transistor gain) values ​​for small signal transistors range from 10 to 500, with maximum Ic (collector current) values ​​of around 80 to 600 mA. Can be found under construction NPN and PNP. These transistors are excellent for use as a small signal amplifier.

Switching transistors:

Small switching transistors are transistors used primarily as switches, but which can also be used as amplifiers. Typical hFE values ​​for small switching transistors range from 10 to 200, with maximum Ic values ​​of around 10 to 1000 mA. Because they amplify the signal with less intensity than other models, they are not widely used for signal amplification, because they have low amplification capacity in relation to small signal transistors. They work as switches and switches, in addition to being found as both NPN and PNP.

In the video below we talked in detail what the hFE of the transistor is, what it is for and mainly how to discover the hFE of a transistor in practice.

Force transistors:

Force transistors are widely used in high current circuits, where a lot of energy is being used (current and voltage). The transistor collector is connected to a metal base that acts as a heat sink to dissipate excess energy.

Power transistors can be found in NPN and PNP structures. They are widely used in parallel with more sensitive circuits, in order to allow current to pass through the transistor, relieving the electronic circuit.

Photo transistors:

The photo transistor is sensitive to light, a common type of photo transistor resembles a bipolar transistor with its lead from the base removed and replaced with a light sensitive area. That is why a photo transistor has only two terminals instead of three. When the light-sensitive region is exposed to a luminous intensity it starts to conduct electric current, otherwise it behaves like an open switch.

We finish this article here and we hope to have helped you to clear all doubts about the transistors! If you still have any doubts or curiosity about this matter, leave it in the comments and we will respond.