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Subido el 20 de junio de 2019 por Isabel L.

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Well, in second official, we have already studied some important electronic components such as a light-dependent resistor, potentiometer, and so on. 00:00:01
So, we will use these components in this year, but we will also study one very important 00:00:16
component that is new for you, which is transistor. 00:00:29
So in this lesson we are going to review semiconductors, the diodes and its way of work. 00:00:33
sister which is new and that are basically the component more characteristic in 00:00:46
analogical electronic. Firstly, well, we know that the materials can be 00:00:56
divided into insulators and conductors but there are also some materials and 00:01:09
also some components that sometimes can be conductors and sometimes can be 00:01:18
insulators. It depends of the quantity of energy. One of these is silicon. Silicon 00:01:23
as you can see in this slide, is solid at a temperature, at our temperature. So what 00:01:34
happens if you, for example, give silicon sun energy such as light or heat, the links 00:01:51
between two atoms of silicon in the net can be broken. 00:02:03
So if one of these links is broken, what happens? 00:02:09
Well you have an electron that can move in the net of silicon, so the silicon changes 00:02:17
from insulator to conductor but you also have a hole in the net of silicon so a silicon can 00:02:25
be a conductor because it has electron free electrons and also free holes electrons are 00:02:35
negative charge, negative loads, and holes are positive loads. 00:02:43
Can also improve if you change one atom of silicon, one atom of silicon in the net is 00:02:52
changing to other kind of atoms, for example, if you change one silicon and 00:03:04
exchange the silicon with a boron, we have one less electron, what you have is 00:03:15
is a hole, so this is a conductor because it has positive chairs that can move on the net. 00:03:25
If you have instead of silicon, phosphorous, phosphorous has an extra electron, 00:03:36
So you have a semiconductor type negative because you have a free electron in the net of silicon. 00:03:44
So, what happened? Well, usually we have one part of silicon with excess of holes or positive charge and another part with excess of electrons or negative charge. 00:03:56
In this case what you have is a diode. So it's the first component with this solid. What happened? That obviously in the joint zone the electrons and holes tend to culminate so you have an electric current because of this. 00:04:22
If you have electric current, you also have a voltage, so you can draw what happens, what is the relationship or the ratio between the voltage in the diode and the current in the diode, which is something intrinsic of the diode. 00:04:50
it just only depends on the numbers of church holes and electrodes, so it just only depends on 00:05:15
how the makers have made this diodes. It's not something extrinsic, it's something external 00:05:29
of the diode is something that depends just only the material. 00:05:41
So this is the characteristic of the diode. 00:05:46
Other thing is when connect the diode to a power supply, for example battery. 00:05:51
What happens? 00:06:04
You can connect the diode in two ways. 00:06:05
which is the way in the directed polarization in this case what you are doing with the external 00:06:08
churches is push internal shakers but you can also connect the yodo against the internal 00:06:18
current in this case is inverse polarization if you do pushing the 00:06:27
internal current obviously you have this case is in this part of the 00:06:39
characteristic cure but in the you do against what usually happen is that you 00:06:45
need to overcome voltage and sometimes it can burn the diodes, just only thinner diodes 00:06:54
can work in these conditions. 00:07:07
So in this case, what you have is that, depending on the external parameters, the warp point 00:07:12
is different. 00:07:24
So you can have the characteristic of the diodes and also the warp line. 00:07:26
And between two lines there is an international point, which is the warp point. 00:07:38
And in this point there are the gases still constant that you do. 00:07:47
Logically, you usually use a point which is also always in saturation. 00:07:52
So although it is true that the work point in a diodo is not always the same, it does 00:08:02
not always have the same voltage and the same current, we can consider that the voltage 00:08:13
in a diodo is always 0.7 volts. 00:08:20
And you can also have other solid components, in this case is transistor. 00:08:33
Transistor can be bipolar or unipolar, it depends of how you make this transistor. 00:08:46
Well in a bipolar transistor what you have, you have three parts, base, emitter and collector. 00:08:58
The parts depending of the external dopage. 00:09:09
So you can have a PNP transistor or NPN transistor. 00:09:15
In any case, the current in emitter is the addition of the current of base and collector. 00:09:25
But the sense of the current are different in any case. 00:09:38
So the way you have to connect the transistor to the battery depends on the type of transistor. 00:09:43
You must take into consideration the polarity. 00:09:58
Well, as you have in the diodo, in this case you have a characteristic of transistor. 00:10:04
A characteristic curve of transistor is in this slide in blue. 00:10:14
So in this characteristic you can distinguish three zones. 00:10:20
a zone in which you have the transistor cut, so it works as an open interrupter, 00:10:26
there is another zone which is the saturation region in which the transistor 00:10:40
always is like a closed interrupter and the voltage is 0.2 volts below and between these 00:10:48
zones the voltage between collector and emitter and connector depends of the current that are 00:11:02
through the base so is the active zone and as the same happened in the in the 00:11:16
diodo in this case you can have difference a good point one point it 00:11:28
depends the external a external condition it depends of the voltage of 00:11:39
battery and the pencil the current that the battery makes that are in through the 00:11:48
the the transistor we will do a problem in which you can understand all of this another important 00:11:57
thing is the relationship between the current that you have through the base and the current 00:12:09
that you have in the emitter. Transistor is a small amplification, so the relationship between 00:12:17
the current in the collector and in the base is what usually called transistor gain. Well, 00:12:32
very often is 100 more or less. Well in this case for example you have an example or in which you 00:12:42
can calculate all the parameters we have in this case how you can calculate for example the current 00:12:58
in the collector, the current in the base and so on. So the only thing that you have to do is 00:13:10
have an application of Ohm's law. But we will do another example that can clarify you all of this. 00:13:19
Apart from the transistor, you can also have, for example, other types of transistors, which 00:13:30
are usually called unipolar, but what happens nowadays is that, for example, in transistor, 00:13:45
we come to states current cutoff and saturation. So you can associate this state with O and 1. 00:13:54
So you can transform analogic electronic into digital. And nowadays we usually do, 00:14:07
because digital electronic is very easy and it's very useful and it's what we are doing nowadays. 00:14:16
Idioma/s:
en
Autor/es:
Isabel Lafuente
Subido por:
Isabel L.
Licencia:
Reconocimiento - No comercial
Visualizaciones:
23
Fecha:
20 de junio de 2019 - 18:55
Visibilidad:
Público
Centro:
IES JAIME FERRAN
Duración:
14′ 36″
Relación de aspecto:
1.78:1
Resolución:
1920x1080 píxeles
Tamaño:
192.62 MBytes

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