The transistors are one of the most used components in circuits of electronic components. They are present in most devices, from old radios, through your mobile and even in space rockets.
Creating this component is a bit confusingsince the first record dates from the year 1925, but it was not until 1947 when he found a true use and was given a name.
The term transistor derives from the combination of the components, thermistor and varistor. This investigation was worth Nobel 1956. If you want to know more about this topic, continue reading.
What is a transistor and what is it used for in an electronic system?
A transistor is a device that regulates the flow of current or voltage 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 in this way carry out one or another action.
- It works as a signal amplifier element. When a small current signal reaches it, it converts 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 executed?
To understand these three states we are going to do it through a hydraulic scheme, which is easier to understand. Imagine that the transistor is a faucet, like the one in the figure. (We will talk about water to understand how it works, but you only have to change the water for electric current and the water key for the transistor). In the image we see the faucet in three different states.
So that the key goes up and can pass water from the pipe “AND” towards the pipe “C” it is necessary that some water enters through the small pipe (B) and push the key upwards, so that the square of lines rises 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 next:
cutting operation
If there is no pressure at B does not pass water through your pipe and leaves the valve closed, so it does not open and does not produce a passage of fluid from the emitter (E) to the collector (C). The valve is at rest and does nothing.
active operation
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”.
Saturation operation
If enough pressure comes through “B”, the valve will open fully and all the water will be able to pass from the emitter (E) to the collector (C). It is the maximum amount possible, no matter how much we increase the water pressure per “B” the amount of water that passes from “E” to “C” is always the same, the maximum possible that the pipe will allow. As you can see, a small amount of water per “B” allows much more water to pass between “E” and “C”.
General operation
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 flow of current between the emitter and the collector, in cut it works like an open switch between the emitter and the collector and finally, when the base current is at maximum (in saturation) it works like a closed switch letting pass current between emitter and collector. Also, pass the maximum current allowed by the transistor between “E” and “C”.
- The third case is that a more current reaches the base of the transistor. small amount of 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. that 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 larger current between the emitter and collector.
Types of transistors What are all that exist and how are they different?
being transistors one of the most used components in all kinds of circuits and devices it is normal that there is a great variety of them. This lies in the specific function that it will be given, whether as a switch or an amplifier. Although they are generally made of the same semiconductor materials, the factors mentioned above can vary the size, position, name, and even the number of terminals of a transistor.
Despite the great variety, we are going to describe the most common:
- Unijunction 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 type P material is embedded, which acts as an emitter.
- Bipolar Transistors (BJT). Of the most commonly used, they can in turn be divided into PNP and NPN transistors. The first ones are used for positive voltages and the other ones for negative ones. In analog circuits they are often 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 like resistors and capacitors, allowing you to create entire circuits using only these components.
Construction of a Transistor What materials are used and in what proportions?
The transistors are built according to the need of the application to which they are going to be subjected. However, we can say that they are composed in a similar way. We will use as an example a bipolar transistor or BJT. This transistor has as its main component a single crystal, usually germanium, silicon, or gallium arsenide, which function as a semiconductor (an intermediate between conductor and insulator).
On this element, three sectors are sectioned in a discriminated way, in such a way that it remains 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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