Hello and welcome! Fifth chapter of the basic electronics tutorial, let's talk about ... the diodes A diode is an electronic component that lets the electric current flow in one direction and blocks it in the opposite direction This has similarity with other techniques, for example, in compressed air, the valve of the wheel of a vehicle ... Let the air pass into the wheel but not out Well, the diode does the same except that, instead of air, it does with electricity. That is its main characteristic: to let the current pass only in one direction, but this is not its only characteristic We will see that there are many types of diodes, and they do many more things Currently, a diode is made of a material called "semiconductor" Which has allowed the electronic revolution by the miniaturization of circuits I'll talk about semiconductors at the end of this video, in the "corner of theory" Before semiconductors were used, the diodes and other electronic devices were based on vacuum valves or thermionic valves They were quite large, they generated a lot of heat, they had a high consumption of electricity ... And all that derived in the present: Semiconductors We are going to dedicate a chapter to the vacuum valves Although they seem obsolete, are still used. For example, in a microwave oven, the element that generates such microwaves is the magnetron, which is a vacuum valve On a TV with cathode ray tube, that tube is a vacuum valve Are also used in broadcasting, for radio-frequency amplifiers. Some of these valves are huge, high power In addition, I think knowing the operation of a vacuum valve (even if they are used little) will help to better understand other concepts of electronics Well, as I said, the diode is based on semiconductor materials, let's see a drawing ... This is the symbol normally used in electronic diagrams to represent a diode Basically, it is always the same, although depending on the type of diode, some detail can change A triangle and a dash The dash is the cathode, and the other side, the anode Here, a drawing representing a diode, and here, a real diode Here above we have the representation of how a diode is made internally With two semiconductor crystals, one of type N and another of type P Both crystals are made of silicon, germanium ... And to each of these crystals are added a small amount of materials Such as boron, indium, arsenic, antimony, sulfur ... And with these materials crystals of type N and of type P are created When two crystals are joined (N and P), in the zone of union occur phenomena at the atomic level that make it conductor of the electricity in only one direction. I want to make clear what is the symbol for a diode: It is always a triangle and a dash As I said, this may vary slightly depending on the type of diode At the end of the dash we have the cathode, negative terminal. At the other end, the anode (positive) Here we have the drawing of a typical diode, not all have the same shape, we will see some exception In this type of diode there is always a narrow strip with a color different from the rest of the diode. This strip represents the cathode. Thus, we can match a real diode with the symbol of a diode in a schematic and we will know in which position it is necessary to put it A paradoxical fact in the diodes is that the electric current actually flows backwards from the arrows That is, the current will flow here, but not the other way round We must forget old conventions that say that electricity travels from the positive to the negative. That is not like that The electricity circulates from the negative to the positive, because what circulates in an electric current are electrons, not protons ... We are going to see an exception in the form of the diode, for example an LED There you have one Here the terminals are recognized because the cathode is always the shortest terminal But what if someone has trimmed the terminals? This advice no longer serves us ... The LEDs are almost always transparent or at least translucent In this drawing of an enlarged led We see that the electrodes inside have a very different shape and size. The cathode is always the large electrode. Yes, a diode has polarity, but it has the special quality that it can be connected in both ways, according to the application that will be given. Of course, in a given application we can not change the diode as we like. You have to respect its polarity, its position. I mean that it can be connected in both ways according to the application that will have that diode The first way to connect it is: Match the positive terminal (anode) to the positive voltage. And connect to the cathode (negative) the negative voltage Here, the current will circulate. Remember that the current will be reversed as indicated by the diode symbol arrow. Here I have written an imaginary current And here, a limiting resistance because if an LED is connected to more than 3 volts can be destroyed This would be the FORWARD polarization To use REVERSE polarization, we can invert the power polarity or invert the diode position. I have done the second Now the current will not circulate (the diode points in that direction) The current will be zero, or almost zero How does a diode behave? The response curve tells us a lot. Let's go to see her... In the characteristic curve of a diode we have two axes: One horizontal for the voltage, and one vertical for the current Here we have the zero, towards the right is growing the positive voltage (forward polarization) and to the left of zero, there are negative voltages (reverse polarization) As regards the axis of the current, upwards are positive currents, and downwards they are negative currents. The "positive" and "negative" refers to the direction of the current Starting from zero volts applied to the diode We are raising the voltage and the diode does not conduct the current until it exceeds a value known as threshold voltage From which the diode begins to conducts That threshold voltage is small, typically 0.7 volts for silicon diodes, 0.3 for germanium and even less for schottky diodes Once the diode starts to conducts, we have another parameter that is the maximum current That is, the maximum current that can withstand without being destroyed Now, let's deal with the reverse voltage We apply reverse voltage, but the diode conducts very little This reverse current is very small and is another parameter of the diode when reverse polarized If we increase more the voltage we arrive at the breakdown voltage (another parameter of the diode) When the voltage reaches that threshold, the current grows abruptly and usually involves the destruction of the diode So we have four parameters in the curve Threshold voltage, maximum forward current, reverse current and breakdown voltage About breakdown voltage, is not always an unwanted phenomenon Although most diodes are destroyed by reaching the breakdown voltage There are other diodes, such as zener, where the breakdown voltage is used to our advantage without the diode being destroyed As long as we do not exceed a certain value of inverse voltage. Next we will see the zener diodes The avalanche breakdown is caused by the heat generated by the weak reverse current That heat causes more conduction in the semiconductor material, which in turn generates more heat ... each factor increases to the other factor, so that reaches a point where the current rises explosively and the diode is destroyed This can be compared with the fact of mechanically compressing a glass vessel And we will see that as we increase the force, the vessel does not flex nor show signs of weakness. The glass does not warn But at an applied force level, with no prior signals, it breaks Well, the diode does exactly the same thing A diode that has undergone the avalanche breakdown becomes unusable And if we measure it with the tester, it will give us continuity in both directions, that is, zero ohms. Internally short-circuited. That diode is no good anymore There will be times when you will be interested in knowing a data, a parameter of a diode ... Perhaps its maximum current value, or its breakdown avalanche voltage ... or any other data If you are repairing a device, this issue is not going to worry you much because in this case the concern is to replace the component with an EQUAL, and there is no more But if you are designing, creating a circuit, if you may need to know, for example: This diode is a 1N4148. Can handle this diode half ampere? Well, the way to know this and much more is to consult the "spec sheet", datasheet in English For that we are going to go to the Internet, and in a search engine we type the code (1N4148 in this case) and as a result we'll get a good number of pages In some pages they ask us to register, others, I have seemed to see that they are for payment. But there are many free pages I typed "1N4148" and entered this page. Ahead! we'll see a lot of data on this diode ... There is information about the package, ie the physical form Their dimensions, electrical characteristics, voltages, currents ... even ... More advanced data such as parasitic capacity, working temperatures, what they are used for ... And also the equivalences, which is an important concept in semiconductors Two equivalent components are components with different code but that can be used interchangeably since they have similar characteristics These are the symbols normally used for the diodes in the diagrams The first, the diode rectifier, the most common, the most frequent The zener diode, of these three drawings I most often see is this central And then two diodes that we will see on few occasions because they are very specific: The varicap diode that is usually inside the tuners ... ...to search for stations, tuning The tunnel diode is used for high frequency applications Other widely used diodes are the well-known LED light emitting diode The photodiode, which does the opposite of the LED, depending on the light it receives, will conducts more or less And finally, the Schottky diode, widely used in power supplies, is very fast and has very little voltage drop. So, the main feature of a diode is that it lets the current pass in one direction but not in the other, however ... Due to the large number of diode types that exist, depending on the manufacturing process ... In fact, I just showed you a drawing and there were seven types of diode, well ... Some of these types of diodes, it happens that the main feature is in the background Because they exhibit some special quality, for example, in the case of LEDs what interests us is that they emit light And the fact that they conduct in one direction or another is less relevant Let's take a look at the different types of diode To continue with the same order, we start with the rectifiers diodes The symbol, appearance, and two real diodes These two are type BY127 and 1N4148 These diodes have many applications, many uses But its main task is to rectify, that is, to convert the alternating current in direct It can be rectified with a diode, with two and four, this is one of my favorites, it is full wave, it does not lose any current There is an alternative to this set of four diodes, it is the bridge rectifier Their connection is simpler, since they only have four terminals. AC input, these two nd positive and negative output, and we avoid to solder eight terminals of four diodes I recommend this option, it is more compact Another application for the diodes rectifiers is in the circuits of maneuver to govern electric motors Make them spin in one direction or another, activate electromagnets ... The diodes, thanks to its unidirectional characteristic, allows us to provide logic to these circuits Another, quite common, use that can be given to a rectifier diode is as protection If a diode is placed in parallel with the power supply of the circuit to be protected ... ... if inverted polarity is applied, the diode (and fuse) is destroyed but the equipment is saved The destruction of the diode is a lesser evil, since a diode costs a few cents Another type of diode is the detector diode In broadcasting, whether radio, tv, satellite, any communication system ... We have to transmit two signals: The signal that carries the information, the useful signal ... ... and the carrier signal, which is the one that carries the useful signal, the information Let us focus, for example, on the radio. Sound is transmitted, at a low frequency, from a few HZ to several thousand HZ However, radio frequencies are typically in the range of megahertz That high frequency is the carrier signal, it is the signal that transports the sound In the transmitter, both signals (carrier and audio) are mixed Well, the job the receiver has to do is the reverse Once the signal is received, the low frequency (sound) and the carrier must be separated. This work is precisely what makes a detector diode Another type of diode is the zener diode A while ago we talked about the avalanche breakdown. This diode exploits this phenomenon If this diode is directly polarized, it conducts as a rectifier diode, but that is not its application This diode must be reverse polarized, and will not conduct until it reaches its zener voltage In this example the zener voltage is 24 volts, so it will not conduct as long as it does not match / exceed that value By matching that 24-volt zener voltage, the diode will suddenly start to conduct This behavior can serve to mark a value reference for a voltage in the circuits Of course, the zener is not destroyed when it starts to conduct, as long as we do not exceed its maximum inverse voltage This is 24 volts, but are manufactured for many different voltages, there are many normalized values So, look for the value you are looking for, you will find it, perhaps with differences of tenths of volt Other type of diode is the LED, the light-emitting diode At first they were simple indicator lights, to signal processes in an instrument panel They were also used in the first electronic calculators, to form the digits by means of 7 segments, (each segment is a diode) But the issue has been derived to this day, in that an LED is not only for signaling but for generating authentic lighting Thus, in the home, in the office, the led lamp already competes with advantage with the fluorescent and the lamp of low consumption because they consume very little and they last a lot A led can emit at many wavelengths We have, for the moment, visible light Here, three visible light led: Red, green and blue, and there are also yellow, orange, white ... there are a lot of colors available. Another widely used wavelength in the led is the infrared. We can not see the infrared, but it's still basically light and the most well-known application is in the remote controls With these remote controls we control the TV, the audio equipment, the air conditioning ... The first remote controls worked with ultrasound, but now they all do with infrared In these remote controls the led is usually visible from the outside By the way, there is a trick to know if a remote control works Is to direct the remote control to a camera (photos, video or mobile) And if we press a key, we will see the light Is perceived perfectly However, directly I do not see anything, but the cameras perceive this infrared This makes the LED a valid component for using in a night surveillance system If in an enclosure not illuminated we put a spotlight with infrared led There is still no light ... visible light But there will be infrared light Any camera will capture everything perfectly even though no one sees anything there Thanks to the feature that ALL cameras are able to detect the infrared Another type of diode that also emits light is the laser diode And here we all remember the most common application that is ... ...read from a mass storage medium like a CD, a DVD or a blue ray Here you have a CD reading unit where you can see ... the lens The laser diode is inside, it is the size of a chickpea and cylindrical shape The LED diode industry, the truth is that it has an assured future Well ... let's finish this part of the led with a test, I'll make it shine... This green led ... With 3.2 volts that I bring from an adjustable power supply, and we will see which light emits negative... to cathode This light is worth as signaling, not a great thing, but it is worth to signal Now we will see a Led of the so-called "high-brightness" which, with the same size and the same voltage, emit much more light, look at the difference ... This is already light "really" Other type of diode: The photodiode. If it is forward polarized it conducts like a normal diode But this is not how this diode is used. It must polarize reversely. In this case it no longer conducts As more light strikes the photodiode, it will conduct more and more This resembles the type LDR resistor but with advantage for the photodiode that has a much higher response rate Photodiodes have many uses, for example, in the industry to automate processes Are used in alarms, toys, communications, in the remote controls that we have seen before ... The equipment governed by this remote control has a photodiode to receive the infrared that comes from here Photodiodes are also used in military applications ... I know that this model of photodiode, BPW34 is mounted by some smart bombs (assuming that a bomb can be called "smart") Make a matrix with four diodes like this one. The laser beam sent to the target, when reflected, according to alignment, will hit one or other of those four Led. And this generates a signal that, amplified, drives an aileron or other, in one direction or another, causing the weapon to be directed with full precision to the target That is, they have many applications I have a machine that I want to put into operation so that you can see the potential of photodiodes This is a montage ... not very practical But, as I say, it will serve to see a photodiode in action There are plants that if a fly lands on them, they close. They are called venus flytrap I wanted to do something similar, mechanically The truth is that the machine works perfectly, but I have not uploaded the video because the flies don't "collaborate" I mean, the supposed chemical attractant ... does not attract them So, here is the machine inactive, I'll show it to see how a photodiode works This is the venus flytrap mechanic. It's based... ... on the case of a CD, mechanized, as a jaw There is an LED that is now emitting. And this photodiode receives that light, this piece here Really is a phototransistor, but basically it's the same ... The difference is that the phototransistor amplifies When a fly is attracted by pheromones here ... The only way they have to try to access is by standing here in the middle, and by interrupting the beam of light ... ... and the photodiode (or phototransistor) sends that variation of current to the circuit ... ... and the circuit using a thyristor triggers the process The electricity stored in these capacitors is sent to this electromagnet which when retracted, drives the "door" down And hit the fly. It does not kill it but it does stun it The fly falls, for example, into a vessel with water Ok, let's try this, the power is Ok, the diode emitting ... And the capacitors will be well charged, it takes a minute to charge ... We put in the middle of the trap a small object ... Let's see if we trip the trap Another type of diode is the varicap diode Is a diode that, normally, we are not going to find "loose" because usually it is part of the tuners This is a TV tuner, here is the antenna input ... And here it has a series of auxiliary input and output terminals such as power supply ... Intermediate frequency output, voltage for varicap ... and more functions Well, here is the varicap diode, which is in charge of doing the search, the tuning This diode we have already seen briefly in the previous chapter "capacitors" because it behaves like a capacitor when applied a reverse voltage This diode barely conducts, but between its terminals there is a capacity and behaves like capacitor The best of all is that this capacity is not fixed, but depends on the applied voltage, so the varicap behaves as a variable capacitor Like those capacitors based on two metal plates that overlap each other, varying their capacity, and served to "search for stations" The varicap diode has an advantage over that classical mechanical capacitor. First, it is not based on mechanics and is more reliable. And, second (very important) is that the tuning in a varicap is done by sending a variable voltage because its capacity varies according to the voltage This allows computerizing or digitizing the station search process For example, on a TV, when we look for stations with a modern tuner like this ... Sometimes a progress bar appears on the TV screen. In those moments what is being done is to send to the varicap a growing tension ... And when the varicap diode reaches a capacity value for which the tuner finds a TV station ... ... the search process stops and gives us the option to memorize that TV station And, what does it mean to memorize a TV station? Is that the voltage value that the varicap diode was receiving upon finding the TV station is converted to a digital numeric format and stored in a memory and then... We can continue searching for more stations and optionally, memorize them At the end of the search process we will have in a memory a table with a series of numerical values corresponding to a specific voltage Later, to see a station that we have saved in that memory ... The TV circuit sends that voltage stored in memory to the varicap diode ... and immediately it will appear on the scene, whether it be radio or TV As you can see, this search system is much more agile and useful than the classic manual with plate capacitor where you have to search the stations again and again Thanks to the varicap diode, the searches can be stored in a memory, as we have seen Another diode is the tunnel effect diode, or simply diode tunnel This is not a diode that we will meet every day, and has quite specific applications Such as high frequency What differentiates the tunnel diode from the rest of the diodes is its strange response curve This is the characteristic curve of a normal diode, where we see that an increase in the direct voltage corresponds to a very high current increase In a tunnel diode things are different. We see that, upon reaching a voltage called "crest", the current decreases rather than increases. It is as if the diode had "negative resistance" All this until arriving at another voltage called "trough" And from this point the tunnel diode again exhibits normal behavior Well, this area, called "negative resistance" ... And makes it useful for working in amplification, especially for high frequencies And we go with the last type of diode: The schottky diode This diode is also very suitable for working with high frequencies This makes it ideal to be used in switched power supplies, you know that in those power supplies... There is an input of 220/125 volts of alternating current and is rectified to direct current This direct current is converted back to alternating current, but this time at a frequency much higher than that of the mains, not at 50-60 Hz but at kilohertz or even megahertz This allows to use much smaller transformers While in a conventional (non-switched) power supply such large transformers were used ... However, these switched sources create a new problem: Some components do not perform well at high frequencies, eg many types of diodes Well, the schottky diode works well at high frequencies By the way, in this channel I have a video dedicated to the repair of a PC monitor and the cause of the fault was a schottky diode There you will see as I locate that diode and replace it. If you want to have a look, here is the link to that video There is something to be said about diode types, although it may be appropriate to say "format" rather than "type" Is the format "SMD", since in this format we have all types of diodes: rectifiers, led, tunnel ... A "SMD" component, in this case a diode, is mounted directly on the printed circuit On the side of the solderings The SMDs do not have wire terminals, but their ends are metallized And are soldered directly. It is best to look at these SMD components This printed circuit board has a good collection of SMD components We identified here a pair of diodes ... This tubular component is a diode This one here is also a diode There are also SMD capacitors and resistors... Also integrated circuits, transistors with its three terminals ... This can be power transistors or mosphets That is, there are all kinds of SMD components You can appreciate the great miniaturization that these components allow It's time to practice, let's see a couple of applications for diodes, although of course there are many more ... But I can not make a video 87 hours long, I have selected the ones that I think are more representative ... Every amateur, sooner or later (rather early) will have to face one of the following techniques ... And I mean, first of all, rectification Rectify is to convert an alternating current into direct current, and we will see two variants First the simplest, medium wave rectifier, somewhat limited And then the full-wave rectifier, a little more elaborate, is the one that is used most of the times And secondly, we will see an artifice or assembly to protect a circuit against reverse polarity We started with the rectification This is the half wave rectifier circuit, the simplest. It consists of a single diode Here is a 220 volt to 12 volt transformer... At its output the 12 volts are also alternating current Here we are going to have negative and positive polarity or vice versa: positive and negative, as the alternating cycle changes We are going to assume that the first half-cycle, (which is positive), the tension here is negative and here is positive We know that the electric current flows from negative to positive The current comes here, goes through the load resistance that prevents an excessive current that would destroy the diode The current comes here, and remember that mnemonic: This diode is going to conduct since its arrow is in the opposite direction The circuit allows to pass to this positive half-cycle and is transmitted integrally to the output through the diode Then the polarity is reversed (this is alternating current) and the negative will be here, above Now the diode will not conduct and this negative half-cycle is not transmitted to the output, here we see as an "electric silence", no electricity is transmitted And again the cycle is repeated, and only the positive half-cycles are transmitted We have managed to rectify the current, but at a price: We have ignored half of the energy although this can be an advantage... ... in case we want to reduce the output voltage This is not direct current like that of a battery, it is pulsating current The task of converting this pulsating current into a straight line, rests with this capacitor, which acts as a filter At the time of the high voltage cycle the capacitor absorbs that voltage, and when the cycle is at zero, the capacitor returns it. The capacitor acts as an electric shock absorber And this way you get this direct current Here are the oscillograms with the three points: The "A", AC input Point "B", the output of the diode, this is its oscillogram And the point "C" which is actually the same point as the "B", but taking into account the damping action of the capacitor This is fine on paper, but let's see a practical circuit, and with the oscilloscope we'll see the oscillograms Well, oscilloscope on, and here materials for the half wave rectifier A 220 - 12 volt transformer We will connect the anode from the diode to the transformer... The cathode looks to the right, well, we connect with alligator clips ... The other terminal of the transformer we take to the load resistor, 560 ohms ... This resistance will avoid an excessive current so that the diode does not break From the resistor, a wire to the cathode of the diode For the moment I will not put the capacitor, although I will have it ready From the diode onwards it is direct current, and before the diode it's alternating current, so we will respect the polarity The negative is the lower cable. We connect the negative of the capacitor to the load resistor ... And the positive of the capacitor to the cathode of the diode But for now, as I say, I will not connect, I just leave it ready I will not put this clamp on now. Then connect it to the cathode of the diode I'm going to connect the oscilloscope to see this oscillogram ... This oscillogram, at the input of the power supply, the alternating current Electrically speaking, the diode's anode It's the same point as this, so what I've connected to the diode's anode And the negative of the oscilloscope I put it to negative, I will connect already the 220 volts ... I'm going to direct the camera to the oscilloscope, and I'm going to put something insulated here to avoid a short circuit in these cables at 220V ... I direct the camera to the oscilloscope, I plug 220V ... Well, we see that the typical oscillogram of alternating current appears If I now place the oscilloscope probe here, to the right (cathode) of the diode ... Only the positive half-cycles should appear. Let's see if this is true ... I simply have to move the probe from the oscilloscope to the diode's cathode and see the oscilloscope now And this is it: We have removed the negative half-cycles, only the positive ones have passed. We have rectified the alternating current as we have seen the oscillogram And now we are going to do the third operation. We want this waveform to flatten out, to become a straight line And that we will do it by connecting the capacitor that I left disconnected ... Its positive terminal to the diode's cathode And you will see how, just connect it, that waveform becomes a straight line That's. Now, in addition to being direct current, it is filtered One thing about this... Here is a voltage scale that causes this straight line to come out, but if the voltage scale is lowered ... We will see a small component of alternating current, there you see ... This alternating component is called "ripple tension" You must ensure that this ripple tension is as small as possible because it can interfere with the equipment you feed. For example in audio, you can generate buzzing in the speakers All this, as for the half-wave rectifier This is the complete wave rectifier circuit Its main part are these four diodes, there are also full-wave rectifiers with two diodes, but this is the most common This configuration is known as "Graetz bridge" it's four diodes connected as you see And we can also resort to the compact equivalent of bridge rectifier, simpler option Here there are 8 terminals to be soldered, but in the compact bridge we have only 4 ... We have two alternating current inputs ... Here the output of positive in direct current, and the output of negative, also direct current. I recommend using this component better than mounting with the four diodes How does this rectifier work ?: As before, we have a negative and a positive in a positive half-cycle The electrons (the negative) enter here, and can not pass through this diode (it's polarized reverse), but can pass through this other diode Over here they can not go so start down the road Comes here, crosses the load resistance, just like before, comes back ... And now the electrons could pass through either of these two diodes, but by this it will not do because they would go to the same pole of departure of the transformer So the electrons will pass through this diode to return to the other terminal of the transformer, closing the circuit We repeat: electrons travel on this cable ... Down through this cable, ... pass through the load resistor ... By this diode do not circulate, since in the other side of the diode is the point from where they initiated their march the electrons So they will do it here Now comes the negative half-cycle and polarity reverses. The negative will be in the upper terminal of the transformer By this diode can not circulate, will do by this By this diode can not circulate, and will circulate through this cable. Despite the inverted polarity (negative half cycle), the current will flow exactly as it was when it was the positive half-cycle And now the current returns through this diode to the other terminal of the transformer (positive now) Therefore, all semicycles are used. There are no "hollows" This has two advantages: One, energy is not lost since all the semicycles (positive and negative) are converted into direct current And second, very important, the ripple tension will be less since it is easier to smooth a tension like this where all the half-cycles are present... ...than before, in which half of the half-cycles were missing therefore, now this direct tension will be of better quality, will be better filtered, the graph will be more straight And these are the oscillograms. Let's try this rectifier with the oscilloscope All prepared, here the materials ... We connect everything according to the scheme ... The two 12-volt transformer terminals go to the rectifier bridge alternating inputs (I'll use a rectifier bridge, it's simpler) So I connect the transformer to the bridge on its AC terminals There is no polarity because it is alternating current. I can put it that way, or vice versa. And we have here the outputs of positive and negative that, according to the scheme, we take them to the load resistor Is the same resistor as before, of 560 ohms And connect one terminal to the positive, and one to the negative With the capacitor I will do the same as before, I will leave it ready but without connecting it at the moment to test first without filtering the voltage The capacitor has polarity, so the negative of the capacitor which is this side ... I connect it to the negative... ... that is any of these points, I connect it, for example ... here And to the positive of the capacitor I will put its cable but for the moment I will leave it to the air disconnected Because we want to see how this works without filtering. Later, I will connect this positive terminal of the capacitor to the positive, but not now We check everything, there are no cables touching each other, everything is fine ... Before connecting the 220 volt power supply I will connect the oscilloscope... No need to connect here because we already know there will be alternating current I'm going to connect it here, at this point ... And that point is the positive output of the bridge rectifier ok And the negative probe of the oscilloscope, to any part of the negative line in the diagram I'm going to put it on the negative output of the bridge, here ... I connect 220v, and let's see what the oscilloscope says Connecting ... Wow, the cable has broken ... We can connect now I put something insulating so it will not short-circuit ... now the other cable has been broken ... The cables were a little crushed ... Do not forget to separate the cables with an insulator, let's see the oscilloscope ... And we clearly see that there are no longer negative half-cycles canceled ... Now all the semicicles intervene, as we see in this drawing All the semicicles are used ... We have succeeded in inverting the negative half-cycle and turning it into a positive one. As I said before, this has two advantages: The first ... ... is that we take full advantage of the energy, and the second is that the ripple voltage will be lower Now we connect the capacitor to check if this pulsating voltage ... ... in direct current without pulsations. We connect the positive terminal of the capacitor to the positive output of the bridge rectifier, as the diagram says The oscilloscope now marks a straight line ... Do you see it? Filtered direct current If you remove the capacitor, the current is again pulsating Again filtered ... Another application for a diode is to protect a circuit against reverse polarity Here we have a device powered by direct current And this is the protection diode As the diagram is, the diode will not conduct. It's as if the diode was not The NEGATIVE goes through the fuse in the circuit, and returns to the positive, but this diode will not conduct If we reverse the polarity and put it backwards, here the negative and here the positive, now this diode will conduct, as if it were a short circuit ... so that the current can not enter the circuit In this fact lies the protection Here two things can happen in this inverted polarity condition If the power supply is small power and has no protection, after a while in this condition, it is likely that the power supply will break But if the power supply is powerful, what is going to destroy is the fuse and probably the diode, interrupting the current, leaving the circuit protected Of course, there are more advanced means to protect against reverse polarity ... For example, circuits based on semiconductors, which cut the current if they detect that the polarity has been inverted There are also seemingly more rudimentary but very effective methods such as equipping the equipment with an asymmetric connector that precludes such inversion of polarity ... but there is always the possibility of error, so this simple wit I think is quite interesting A task that is often presented in the electronics lab is to check if a diode is in good condition. We are going to do it the following way. Checking a diode with the tester is quite simple. We select the scale of ohms (electrical resistance) And we are going to subject the diode to .. this is a 1N4148, a fairly normal diode ... We are going to submit the diode to two tests. One in each direction No matter where we start, but we have to get the following values. In this direction we have ... 40 megohms, which in this tester equivalent to "infinite" resistance. At the moment, this diode is OK (not short-circuited) We now invert the probes of the tester (or invert the position of the diode) And we should read in the tester a value of thousands of ohms Careful not to touch the probes because we can falsify the tester reading ... in effect, we have 650K (650,000 ohms) This is a typical resistance value for a diode that is in good condition We are going to test with another type of diode, similar, a BY127 We do the same, we put the probes ... We should not touch them And read a value of ... infinite (40 megaohm), look what happens if I touch the probes Now it is measuring my resistance, not the diode, so we should not touch the probes ... now remeasure 40 megohms Now we revert (diode or probes) and we should read a value of several thousands of ohms This diode is also OK. 720 K ohms approximately We have seen diodes that were good, now we are going to see diodes in bad condition One of the most common faults: shortcircuited diode A diode will be short-circuited if the tester measures a resistance zero or near zero ohms This same diode that I used before, I will submit to the avalanche breakdown phenomenon Connecting it to 220 volts but with the precaution of putting an 8 amp fuse in series so as not to trip the breaker We put the fuse with a pair of alligator clips ... The other side of the fuse to this cable, which will bring 220 volts ... the fuse... And with this pair of alligator clips, back to 220 volts The fuse will surely be destroyed and I hope the diode too. Let's see if the breaker does not jump ... Yes, it has jumped, yes ... Well, I've restored the power supply, let's check this diode ... tester selected in ohms ... Exactly, this diode is completely short-circuited. We have an unusual value for a diode of only 1.4 ohms, when normal ... is that it is "infinite" or "many thousands of ohms" This diode is totally useless This type of failure is not uncommon to find it in power supplies ... It is not uncommon for a diode to shortcircuit. If we reverse the probes, the reading is the same: 1.4 ohms. There is another type of fault in a diode and it is the opposite of the above: Instead of being short, it conducts nothing. In neither way. We measure with the tester and it gives us "infinity" in both directions Actually, I've never seen this type of fault on a diode. Whenever I have seen a bad diode, it has been by short circuit, but there is the possibility of an interrupted diode ... I will say that these tests with the tester in a diode for high voltage, those used in microwave ovens can create confusion, since the tester will read "infinite" in both directions Since the battery of the tester does not have enough voltage to overcome the threshold voltage of these diodes, and always reads infinite, and makes us believe (wrongly) that the diode is wrong So, these high voltage diodes should be checked with an artifice such as the one I use in my microwave repair video tutorial I show you a fragment of that video ... To check a high voltage microwave diode there are several modes, I like ... The method of connecting the diode in series with a filament bulb Observing the behavior of the bulb, we can deduce the state of the diode We know that a diode conducts the current only in one direction And the domestic alternating current changes direction 50-60 times per second So that if the diode is in good condition it will only conduct half the time Suppose that only during the positive semicycles If we represent the alternating current in its sinusoidal form ... The diode will only conduct in these positive half-cycles, but not in the negative ones The result is that the bulb will shine half, and in addition with a notorious flicker We do the assembly ... For that, we removed the diode from its site ... Of course, we have previously done the protocol of discharge of the capacitor ... The diode goes with a faston connector, not soldered Before making the assembly I will operate the bulb directly at 230 volts, without the diode, to see how strong the bulb shines In this way the bulb shines at 230 volts Now we put in series ... the diode We make sure that there is no short circuit in these cables ... Now with the serial diode, the bulb should shine with half strength Effectively ... besides, it shines with a flicker that is appreciated quite well ... This is a sign that the diode is in good condition We could have had three different results: One, it would be that the bulb does not shine at all. In this case the diode is cutted (interrupted) and we have to replace it Another result would be that the bulb shines normal. It means that the diode conducts in both directions, ie diode short-circuited. It should also be replaced And a third case, which would be the one I just made, where the bulb shines half, a signal that the diode conduct only half of the half-cycles. That indicates that the diode is fine, and we would put it back in its place. Otherwise we replace it with one equal, and problem solved ... We are coming to the end of the video, in the Corner of Theory we are going to see about the semiconductor materials By "semiconductor" we can understand two things that are basically the same A semiconductor is a substance or material that was invented a little more than half a century ago, and I say "invented" and not "discovered" because it does not exist in nature. A semiconductor is artificial Are based on elements such as silicon and germanium To which small amounts of other materials are added to create crystals with a special electrical behavior Is also generically referred to as "semiconductor" to electronic components that are based on such materials, for example ... The transistor, entirely based on semiconductors, is the most important component in electronics, it is like an electric valve Which can regulate large amounts of electric current by operating it with small amounts of electricity. That is, it is like an amplifier Currently, a normal transistor has this shape and size. Compare it with what was before the emergence of the transistor, which were vacuum valves (this is not a vacuum valve, is a lamp) but has an equivalent size Look at the difference, but this is not the only thing in favor of the transistor. The vacuum valve consumed much more electricity, and generated a lot of heat Was more likely to fail due to working in extreme conditions, and a short service life, with hours counted and there are still more ... Does this transistor look small? Many years ago, there is technology to integrate several million of these transistors, with microscopic size, all in a surface equivalent to a coin, in an assembly known as "chip" or "integrated circuit" And this is the main reason why electronics has advanced so much. For example, just over 50 years ago ... One of the first computers was able to do a few operations per second, that in those years was "The Ultimate..." And this computer occupied a whole plant of a building Generated a lot of heat, and an electric consumption equivalent to 20 houses Well, at the moment you can have that same calculation capacity, .... not the same, but thousands of times higher, in a device the size of a hand, with less cost, consumption, breakdowns, noise ... Thanks to ... semiconductors And how are semiconductors made? Well, you know that each of these videos comes accompanied by an article in my Blog "100ciaencasa" Maybe the theoretical part is better to see it there in the blog But I anticipate that the semiconductors, as I said, are based on a series of chemical elements ... elements of the periodic table, such as silicon and germanium ... ...to which are added other substances, and with this are created two types of crystal Crystals type P, and type N. Let's see a diagram ... Here, as a semiconductor-based diode is made With two crystals. One of type P, and another of type N Here the electrodes or terminals of the diode, and this is the zone of union of both crystals, where the semiconductor phenomena occur Here we have a schematic of a transistor, based on three crystals, since they are three terminals: emitter, base and colector... In the base we have one type of crystal, the other two electrodes will be of the opposite type There's complementary transistors : The base may be type P, and the other two electrodes are type N Therefore, there are transistors type "PNP" and type "NPN" About this we will speak more in the next chapter of this tutorial that will be dedicated to the transistors And what are the components that are based on semiconductors? We have: The diode, which we have seen in this chapter The transistor, to which we are going to dedicate the next chapter The integrated circuit, which is actually a collection of different components encapsulated in a surface Triacs and thyristors are also made with semiconductors, to which we dedicate a chapter The diac, which is a special bidirectional diode ... A not very well known component, the Peltier cell, which converts electricity to cold / heat and vice versa, is also based on semiconductors The semiconductors are not perfect, they have their weaknesses, and one of the worst things for them is the excess heat, which can come in several ways One of these forms would be because of the environmental conditions, it is not necessary to cover the ventilation slits of the domestic appliances because the semiconductors can get to be destroyed Those who have a PC with a special CPU, cooled sometimes even with a water circuit, know very well what I mean when I say that the semiconductors must be kept below a limit temperature Another source of heat that can be fatal to a semiconductor is the heat generated by it itself when it is operated As we have seen with that diode that I destroyed by applying 230 volts, despite the fact that the fuse worked That brief moment has been enough to irreversibly destroy it We can also, involuntarily, destroy ourselves a semiconductor in soldering jobs if we are not careful ... and also with de-soldering jobs, of course In the article of my blog you have some recommendations to avoid this risk Another factor that can destroy a semiconductor is static electricity Agree that many semiconductors are quite robust, like the diode we have manipulated, and they are not going to be broken by a small spark of static, for example of our clothes But there are, for example, integrated circuits that can be broken with that spark of static electricity, and the worst thing is that, a circuit susceptible to be broken by that, is not usually cheap With this, we finished the fifth chapter dedicated to the diodes By the way, do you know what a diode said to a resistor? "RECTIFY IS WISE" What a prat the diode... Well, see you in the next chapter, the sixth, with the transistors bye, bye...
