The transistors are one of the most used components in electronic components circuits. They are present in most devices, from old radios, through your mobile and even in space rockets.
Creating this component is a bit confusing, since the first record dates from the year 1925, but it wasn’t until 1947 when he found a true use and was given name.
The term transistor is derived from the combination of the components, thermistor and varistor. This investigation was worth the Nobel 1956. If you want to know more about this topic, keep reading.
What is a transistor and what is it used for in an electronic system?
A transistor is a device that regulates current or voltage flow acting like a switch or amplifier for electronic or electrical signals.
It basically has two functions:
- Pass or cut electrical signals from a small command signal like a switch. It opens or closes to cut or let the current pass through the circuit and thus carry out one or another action.
- It works as a signal amplifier element. When a small current signal hits it, it turns it into a large one and returns it to the circuit. However, the transistor can also serve as an oscillator, a computer, and a rectifier.
Operation of a transistor What are its main functions and how are they performed?
To understand these three states we are going to do it through a hydraulic scheme, which is easier to understand. Let’s imagine that the transistor is a water tap, like the one in the figure. (We will talk about water to intuit how it works, but you only have to change the water for electric current and the water tap for the transistor). In the image we see the water tap in three different states.
So that the faucet rises and water can pass from the pipe “AND” towards the pipe “C” it is necessary that some water enters through the small pipe (B) and push the faucet up so that the square of lines goes up and allows the passage of water. If we want to place the real names, we will notice in the image that “B” is equal to base, “E” is equal to emitter and “C” is equal to collector.
Let’s see below:
Operation in court
If there is no pressure at B no water passes through its pipe and leaves the valve closed, so it does not open and there is no flow of fluid from emitter (E) to collector (C). The valve is at rest and does nothing.
If we send some water pressure through the base (B) the valve will open depending on the pressure that arrives, beginning to pass water from “E” to “C”.
If enough pressure comes through “B”, the valve will open fully and all the water will be able to pass from emitter (E) to collector (C). It is the maximum amount possible, no matter how much we increase the water pressure by “B” the amount of water that passes from “E” to “C” it is always the same, the maximum possible that the pipe allows. As you can see, a small amount of water per “B” allows much more water to pass between “E” and “C”.
Now let’s replace the water with electric current and the faucet with the transistor:
- In a transistor when no current reaches the base there is no current flow between the emitter and the collector, in cutoff it works as an open switch between the emitter and the collector and finally, when the base current is at maximum (in saturation) its operation is like a closed switch letting pass the current between the emitter and the collector. Also, the maximum current allowed by the transistor passes between “E” and “C”.
- The third case is that the base of the transistor reaches a current more small of the maximum base current for the transistor to open. Then between emitter and collector an intermediate current would pass that will not reach the maximum.
As you can see, the operation of the transistor can be considered as a switch which is electrically actuated by means of current in “B” instead of manually. But it can also be considered a current amplifier because with a small current in the base we get a greater current between the emitter and collector.
Types of transistors What are all those that exist and how do they differ?
Being transistors are one of the most used components in all types of circuits and devices it is normal that there is a great variety of them. This lies in the specific function that will be given to it, either as a switch or an amplifier. Although they are generally made with the same semiconductor materials, the factors mentioned above can vary the size, position, name and even the number of terminals on a transistor.
Despite the great variety, we are going to describe the most common:
- Single junction transistors (UJT). The interior structure is made up of two semiconductor materials. The first of type N in the form of a block that in turn has two bases, between which a material type P is embedded, which acts as an emitter.
- Bipolar Transistors (BJT). Of the most widely used in general, they can in turn be divided into PNP and NPN transistors. The former are used for positive voltages and the others for negative voltages. In analog circuits they are usually found as amplifiers, while in digital structures they are used as switches.
- Field effect transistors (FETs). They are named this way because they generate an electro-field that controls the behavior of the device. One of the advantages of this type of transistors is that they can be controlled as resistors and capacitors, allowing to create entire circuits using only these components.
Construction of a Transistor What materials are used and in what proportions?
Transistors are built according to the need of the application to which they are to be subjected. However, we can say that they are composed in a similar way. We will use a bipolar transistor or BJT as an example. This transistor has as its main component a single crystal, usually made of germanium, silicon, or gallium arsenide, which function as a semiconductor (an intermediate between conductor and insulator).
On this element, three sectors are divided in a discriminate manner, in such a way that NPN or PNP. The second letter always corresponds to the base and the rest to the collector and the emitter. It is important to clarify that, although they are of the same type, they have a different degree of contamination.
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