The transistor is an electronic component capable of acting as a switch and also as an amplifier all through a small electrical signal
and without moving parts. These characteristics have made the transistor become the main component from virtually any electronic device we can find such as the phones we use every day or computers like the one I used to render this video. In fact, a computer's processor contains millions of transistors and companies like AMD are already producing transistors with a lithographic resolution of 7nm (nanometers) that would be 20,000 smaller than a human hair !! In fact, they are so small that this comparison does not help us visualize anything ... I really just wanted to do this simulation Haha In this video we will see how a transistor works internally, its benefits and a bit of history To understand how a transistor works We must first understand how a diode works. Luckily, I already have a video on the subject so I recommend watching it before but I will try to explain the essentials anyway. If we have a circuit with a lamp and an energy source, the energy will pass freely this, because electrons can move freely between metal atoms and when connected to the power source they are forced to move. By adding a diode to the circuit, depending on its position the current can pass freely or be stopped and the reason why this happens is because of its composition Inside the diode there is a semiconductor material such as silicon more specifically, two types of this material. If we took a piece of pure silicon
and saw its atomic structure we will find that each atom has four valence electrons which are shared with four other silicon atoms around it forming a crystalline structure with covalent bonds that is, they share their electrons and therefore have a total of 8 valence electrons per atom resembling noble gases
the most stable elements known to man. If you don't like chemistry, don't be scared. The important thing here is that you understand that eight electrons per atom is the magic number that keeps everything tightly connected in fact so strongly connected that when a new electron wants to go through silicon , the electrons that compose it cannot move hindering the flow of current But this can be changed through a process known as doping. in which impurities are added to silicon to control its conductivity and convert it into a semiconductor of type N or type P If we add impurities that have five valence electrons instead of four then we will have atoms with a total of nine electrons and since eight was our magic number we could say that one of the electrons will be left over or be freer from others which will allow when we connect it to a power source He can move and act like a driver. This alloy is known as a type N semiconductor because it has surplus electrons, which, remember, have a negative charge On the other hand, if we do the doping with impurities that have three valence electrons we will have atoms with a total of seven electrons that is to say that we would have a gap allowing electrons to move through it and generating a movement of the gaps in the opposite direction Since this alloy would have an electron less than the stable form it would have a positive charge. and it would be called semiconductor type P Moreover, to simplify the visualization we will say that each hole corresponds to a positive charge. In this way, when we connect these two types of semiconductors, since their charges are opposite these will attract just in the union. And by applying a voltage source we will have two possible results in the first case, if the positive pole is connected to the type N semiconductor and the negative pole to the semiconductor type P semiconductor charges will attempt to move in opposite directions preventing the flow of current. This is known as reverse polarization. In the second case, if we reverse the polarity of our source N-type semiconductor free electrons will jump through the P-type semiconductor games allowing the passage of the current. Although there is a small detail since in their resting state the atoms are attracted by their opposite electric charge it is necessary that the applied voltage be tall enough to break that union and continue the movement. This voltage is known as a potential barrier. and for a silicon compound diode corresponds to 0.7 volts while, for other materials such as germanium, its value is 0.3 volts. Now that you understand how semiconductors and diode work We can finally understand how a transistor works since basically a transistor are two fused diodes although with some restrictions that we will see next. If we add a type N semiconductor section to our original diode at the beginning and we reduce the thickness of the semiconductor type P we will have the basic structure of a transistor. As you can see, if we ignore the part of the right what we have left is a diode and if we ignore the left part we will have another diode but inverted Which basically means that regardless of the polarization of the voltage source that is connected, the current will not be able to pass that is, it will act as an open switch. But now comes the interesting if we want a current to pass through our transistor we can add a small voltage difference in the semiconductor type P what will happen is that the section on the right will act as a diode in direct polarization letting the current through but not only that when starting the movement of electrons in the semiconductor type p the electrons in the type N semiconductor on the left they will seize their opportunity and also begin to move Note that this only happens because the p-type semiconductor is extremely thin so don't try to make a transistor with two diodes because it won't work for you This behaviour It is especially useful if the voltage between the connector on the left and on the right is greater than the voltage between the lower connector and the one on the right as this would mean that when sending a signal with a small voltage we would be obtaining as a result a signal with a higher voltage and that is why it is said that a transistor can act as a signal amplifier. Or also as a switch if it completely prevents the flow of current. The transistor we just saw is known as NPN bipolar junction transistor and now that they understand how it works let's talk a little about your connectors. The connector on the left is called a collector and the one on the right emitter and among them there is a high potential difference while the type P semiconductor connector is known as BASE and upon receiving a low voltage signal it is able to control if the current can be transmitted between the collector and the emitter and also in what quantity. Another way to understand a transistor is to compare it with a stopcock in which, the pipe is the collector the base is the key that controls the flow of water and the emitter is the water outlet. By the way I never say it in the middle of the videos but since I have your attention Remember to subscribe and follow me on instagram where I share the progress of the new videos: D Going back to what they came for if we think that a transistor is simply a switch and a signal amplifier it may seem a fairly trivial component but if we start thinking that in order to replicate its functions we would have to have a circuit like this with a potentiometer and a mechanical switch We will realize all your benefits. They work without moving elements which allows them to have millions of cycles of use without greater wear In addition to having a high resistance to other factors such as vibrations or blows. Because they only require a small amount of semiconductors to work they can be really small, which allows to position a lot in a small area besides requiring less materials for its manufacture although to achieve this, machines with great precision are required. And perhaps most importantly, its response speed is virtually instantaneous which allows them to be used to amplify high frequency and low voltage signals like those generated by a microphone or a guitar. And if that doesn't convince them of the importance of the transistor I remind you that John Bardeen, Walter Brattain, and William Shockley who invented the transistor also received the Nobel Prize in Physics in 1956 This being one of the inventions that have most impacted our lives to this day. Returning to our NPN bipolar junction transistor depending on the voltages that are applied to its connectors this will have four possible states or "operational regions" and to understand them conceptually we will rely on our hydraulic model. In the first case, we will be in the cutting region where the base voltage will be lower than the other two connectors Therefore, the reaction that will allow the passage of current between the collector and the emitter will not start. I mean, our valve will remain closed. In the second case we will be in the active and direct region and gradually increase the base voltage which will increase the flow of current from the collector to the emitter in a direct proportion. In other words the collector current will be equal to the base current multiplied by a factor known as gain which is informed by the manufacturer of each transistor. This region and the gain factor are the most important when we want to use a transistor as an amplifier. The third case occurs when the base voltage It is too high and therefore the transistor begins to act as a simple cable letting all the current from the collector to the emitter and losing the amplification quality of the active region. And finally, the fourth case is the inverse active region that acts in the same way as the direct active region but transmitting the current in the other direction. This occurs because a transistor is symmetric, and therefore can be used in both directions. So what is the point of putting names as collector and sender to terminals? Good they are symmetrical in the sense that both semiconductors are of type N but the amount of doping applied to them and the contact area with the semiconductor type P not necessarily symmetric which produces that one of the directions has a greater gain than the other. Returning a bit to the application of transistors it is common to see that these are accompanied by a series resistance The function of this resistance is to limit the voltage generated at the base since remember we only need 0.7 volts to enter the active region and increasing the voltage will also increase the current that will pass through the transistor and depending on the transistor if the current is very high it could burn it. The resistance must be high enough to limit the voltage and current that reaches the base but at the same time not so high to prevent its passage completely. If this part was not very clear, remember that I have another video about resistance. With everything you just saw, they should already be experts in the operation of a NPN bipolar junction diode but I have news for you, there are many types of transistors. For example, a PNP bipolar junction transistor that, as you can imagine, has inverted semiconductors and therefore acts in a slightly different way but there are also high gain, high frequency transistors MOSFET, FINTEF, Phototransistors ... to quantum transistors and transistors that work by repositioning a single atom. I don't know about you but my brain would explode if we keep adding information to this video so that we will leave for a next chapter. I already have my favorites but if you want me to explain a specific transistor, leave it in the comments.
