The world of electronics is built on transistors. In fact, at present there are practically no circuits without these elements, however, their operation can be difficult to understand, especially if we are not familiar with these topics, hence the importance of knowing their characteristics in depth.
The electric transistor is one of the great discoveries of the 20th century, according to the opinions of many technology experts. In today’s information age, this device has a similar relevance to that of the steam engine in the 19th century. This invention was developed in the 1950s by American physicists John Bardeen, William Shockley, and Walter Brattain, who shared the 1956 Nobel Prize in Physics.
At present, integrated circuits are widely used, which are basically made of small transistors, therefore, they are present in the internal structure of the television, the computer, the LED lamp, the mobile, the portable radio with USB , but also In power tools, for example, a drill, a garden trimmer, a tin soldering iron ( you can find some purchase options here ) and any other device that has built-in chips. This is why some of us are interested in knowing how to test a transistor, but first you have to know what it is.
Transistor: Easy definition
If you want to know what a transistor is, it is good to think of it simply as an electronic device made up of semiconductor silicon crystals, which can basically function in two ways: as a switch in all digital electronics and as an amplifier in analog circuits, so that is present in almost all the devices that we use in our daily life. Transistors generally have 3 pins called base (B), emitter (E), and collector (C).
It is worth clarifying that we mean a bipolar transistor, which is the most popular among the types of transistors. In this sense, the base is in charge of controlling the flow of current and the collector has the function of collecting the electrical charges provided by the emitter. These 3 components are made of semiconductor material that can be of type N or P. Hence you can find an NPN transistor, which is used for positive voltages, or a PNP transistor, which is for negative voltages.
Basic operation of a transistor
We could compare the operation of a transistor with that of a tap, only in this case it is not a water current, but electricity. If we take into account its symbol, we can easily understand how a transistor works; The flow of electrical energy flows from C to E, as if it were a pipe that goes from the collector to the emitter, however, the intensity can vary depending on the current that you plug into the base (B). This means that if you turn off the current at B, no energy will flow between C and E, it is as if you turned off the tap. For this reason, the transistor works very well as a switch.
However, the current at B can go up or down as it passes into the CE tubing, so the transistor is a good amplifier too. This means that if we connect a current that constantly changes in size in B, this proportionally affects the intensity we have in the pipe from the collector to the emitter, so it also fluctuates, since the parts of a transistor are related to each other.
What are the operating regions of a transistor?
To understand why transistor circuits are so useful, we must know that they can have different applications, depending on the use of the three operating regions of a transistor. Thus, it can act as a closed or open switch, but also as an amplifier, according to the amount of voltage that we connect in B.
If we think of the transistor as a shower tap, we can say that the cut-off region is that area of slack in which we begin to rotate a few degrees but the water still does not come out, so we can close it again without anything having happened. In this case, when checking a transistor we say that it is in the cut-off region when the voltage that enters through B is less than 0.6 V, so it is not capable of activating the electrical flow between C and E, therefore, the intensity is zero and the transistor becomes an open switch.
Returning to the example of the tap, you may have noticed that there comes a point where the water flow has its maximum capacity, therefore, even if you keep turning the tap, the same amount of water comes out, since no more can come out. In this sense, a transistor in saturation works the opposite of one in cut-off region. If the voltage of B exceeds the capacity set by the manufacturer, the transistor saturates, letting electricity pass freely between C and E, as if it were a wire, therefore it is used as a closed switch.
This is the case where the voltage across B is midway between the cutoff region and the saturation region. In this way, it is possible to use the transistor as an amplifier, in a similar way to when we regulate the flow of water in the shower, if we turn to the left, more water comes out, but if we turn to the right less, therefore, it is a range that allows you to have more control. An example of this could be the power transistors in a sound system.
Configurations of a transistor
For the polarization of transistors it is essential to know that there are three basic configurations. As a common emitter, where the gain of a transistor is high in both voltage and current, but the voltage is reversed at the output. For its part, when used as a common collector, the transistor has no voltage gain and only inverts the current at the output. But there is a third configuration called common base, where the input signal is applied to the emitter, while the output is through the collector. In this case, there is no current gain, but the bandwidth is wider.