O que é um MOSFET? Aplicações e características!!

Hello guys. Welcome to another video from the ElectroLab channel. Today, we are going to talk about what the MOSFET is, what are the physical and electrical characteristics of that component, OK?

The MOSFET is an extremely important component nowadays in the electronics, widely used in various equipment. Then, we'll know what it is and how it works. Basically, the name comes from Metal Oxide Semiconductor Field Effect Transistor, that is, the field-effect transistor with a semiconductor metal oxide, OK?

It is a literal translation here of the its name and basically it is made up of three pins, the pins are identified as drain, gate, and source in Portuguese and English, Drin, Gate and Source and it's not "sêrce" as many people say, it's Source (Sórce) OK? And in everyday jargon you hear a lot of people talk Drin, Gate, does not translate the Gate, is called Gate and Source, does not translate Source to source. So, it's what most people use, drain, and it has two types, N channel, P channel, OK?

We will see this later this distinction and when it was created, it was created with two different groups, right? The depletion group, types of depletion and enhancement types, OK? the type of depletion it is used less and the intensification one is more used, mainly the N.

O depletion channel normally it only comes in the N channel version and the intensifier version It comes in both formats, right? N channel and P channel. Usually we see a link here from a second pin here at source.

This is the substrate pin, it is internal, but there are some that have the external substrate, in a room pin for a different kind, OK? But most MOSFETs will come with three pins. Detail, remembering that this arrow that has here, on the N channel as opposed to the NPN transient, that the arrow is out, in MOSFET channel N points the arrow in and if is a P channel, this one is an N channel, if it is a P channel a arrow will be out, OK?

Unlike MOSFETs. Within the groups of deletion and enhancement, depletion, he usually has the drain and source contact closed. So for you open that switch between drain and source, you need to inject a voltage at the gate, unlike the boosts which are more used, they have this normally open contact and for you to close the circuit here, allow the passage of current, you will need to inject positive voltages into the gate, this is a big difference between the two being that the most used, as I said, is that of intensification, it is what the people use it more in circuits.

The mosfet applications are various. Among them the switching, switching, where I use it as a key through the gate, reminding me of a very important thing, that unlike transistors bipolar that work with current, that is, they are current amplifiers work with variations of current and current gain o works with voltage, it is very closer to what was a valve, it is regulated by voltage therefore the variation of voltage does not cause it to occur a voltage variation in the drain OK? He can be used, as I said, in switching, it can be used with amplifiers, amplifiers.

It might be also used as a controlled resistance, since is resistance between drain and source it varies according to the voltage I control on my gate so this is a very useful application and among other applications, right? There is a model that is the model double gate, it has two doors here and it is used a lot like frequency mixers, for example, OK? O amplifier is widely used in the linear region of the mosfet, I will comment on this already, right?

The mosfet, it works with basically three regions, the clipping region, the linear region and the saturation region. It's very similar to a transient, right? What you also have the crop regions, working regions, linear region and saturation regions.

to understand how these three regions work, we will have to know some electrical parameters of the mosget transistor. the one of Important parameters you need to know is VGS. VGS is the is the voltage between gate and source.

The other parameter is a voltage that called threshold voltage , is the trigger voltage, this trigger voltage will be precisely that tension that from it you make the transistor goes into conduction, that is, conduct from drain to source, or close the switch and another aspect would be the VDS voltage at voltage from drain to source, which is this voltage here between these two terminals. Well, in the cut region, we will have the following characteristic, VGS will be less than VTH. This means that the voltage between it is less than the trigger voltage, for that the transistor is in cutoff, OK?

She is smaller than threshold voltage, in the linear region, actually known as the region ohmic, because it is not linear along the entire path, we will see this later on the graph, in the characteristic curve it has a piece that is linear, but most of it is not linear, in this region it will have the following condition VGS will be greater than aa VTH . The trigger voltage, the therefore the transistor is already conducting, this is the region of application and the VDS which is the voltage between drain and source , it will be less than VGS. That's the condition she's in the region ohmic the conduction region or the linear region also consisting of within that range and at saturation, when will it have the maximum current available to the device, it will have the VGS condition is obviously greater than the threshold voltage, because he is also driving and also VDS will be greater than VGS minus the voltage of VTH.

In this condition a VDS greater than VGS minus VTH, it will be in the region of saturation. Some important points here regarding the mosfet. The mosfet, it has a gate current, because it has this characteristic of the gate, it is electrically isolated from the drain and from the source.

It is isolated here, I will do it here, this isolation precisely by an oxide layer and this question of him being a field effect transistor, right? One field effect transistor, it is precisely because of the effect of the electric field that is created between the gate and the other parts of the transient, okay? By this isolation you generate a very high impedance here, but it exists and the current virtually it is zero here, the gate current, ok?

the IG she is very close to Zero, it is a very low current. That means that the Z impedance of the do is very high. This gives us makes it much easier for critical applications such as instrumentation inputs, frequencymeter inputs, due to impedance high, oscilloscope inputs, RMS multimeters, electronic multimeters, right?

you have this this great advantage of having a very high impedance precisely because of this separation, this direct electrical contact between the gate and other parts of the mosfet. This is his characteristic. One another issue is having this extremely high impedance, it is very sensitive to ESD.

The discharge of electricity static, right? So i. e.

static electricity is known to be a risk in electronics, right? It's a risk for sensitive components. That's why we use it in some laboratory situations the electrostatic blankets, properly grounded, with wristbands and equipment type grounded soldering iron and everything to protect equipment sensitive like these.

The mosfets in the past or even the FETs, they burned easily if you accidentally touched the gate with a voltage, loaded with a high voltage of static electricity. And today the mosfet has inside it a zener, most of them have a protective zener and avoid a lot of his burning, although he remains a sensitive component, we have to be careful when handling component equipment with mosfets, ok? I say this to loose component.

The component on the board can be burned too, but it's a little more difficult because the potential is just distributed among the various components that are there soldiers. But I would avoid handling equipment or single components that had mosfets implemented, ok? Per account of static electricity due to these high impedances, which are advantages when setting up a project which are disadvantages when handling the component.

I'm going present, for example, the IRF 640 , which is very well known widely used in the market. And by chance this one here, by the way this one, this transistor here it uses the casing TO220 zero AB, which is this model, it has some characteristics for example the maximum drain voltage of it two hundred volts the drain x source resistance, when it is conducting 0. 18 ohms, and the maximum drain current, eighteen amps.

These are values ​​that you have to take into consideration in the project. Some other values ​​very important. One is maximum junction temperature one hundred and fifty degrees, later we'll see why that and the join parameter for environment.

In this case, the R Theta JA, huh? Junction parameter for environment, sixty-two degrees per watt. Other parameters here in the datasheet, is the drain threshold voltage to the source he puts between two and four volts here.

OK? These are features. Some very important issues with in relation to the mosfet are related to its power.

So I made here an example of a mosfet working as a switch here of a load, this load can be a lamp, could be a motor or something. Let's suppose that this load had one ampere draw, it draws one ampere. You have a mosfet here with a control voltage here at the input and you want to verify that it has, say, supports the power that the charge will dissipate.

So, an interesting thing is to make the minimum calculations here to understand how this works power calculation. In this case, the formula will have a power equal to drain x source resistance, which is the resistance in the mosfet between drain and source and the power paid in the transistor, times the current squared, okay? The drain x source resistance we can get it directly in the datasheet, it would be the drain-to-source resistance when the transistor leads, RDson, zero point eighteen ohms, OK?

so i can know the next if I have a load with one ampere and I want to know what power this load will dissipate, will make the transistor at the moment it is consuming its totality, that is 1A, I'm going to do zero comma eighteen times one squared. This is obviously going to give zero point eighteen watts. IT IS consumption is dissipation, right?

small in transistor, a small dissipation. So I have to observe the following, you enter the datasheet and verify that the power of him speaks, something around one hundred and twenty-five watts, the problem is that this power is in the case of the transistor that is operating at twenty-five degrees of temperature in your casing, ok? This may not be a reality, so this value here is usually if the transistor is cold at twenty-five degrees at a temperature environment, so therefore to work like this I need a heatsink, actually I need to calculate what is the maximum power it will dissipate without heatsink heat, okay?

And for that there is a formula, we will check now. Well, the power in the mosfet without heatsink, it has to be calculated as follows, the power maximum, maximum power without heatsink. she will be the maximum junction temperature, which I will find in the datasheet, minus the standard room temperature, divided by the parameter R theta junction to the environment, which I also find in the datasheet, so let's look there.

The maximum junction temperature he tells me here it is one hundred and fifty, maximum one hundred and fifty degrees. So I'm going to put one hundred and fifty. less environment, environment we consider twenty-five degrees.

divided by RTJ A. R tetra JA here, which is the join parameter for environment, is sixty-two degrees per watt, sixty-two. So let's do this math here quickly on the calculator one hundred and fifty minus twenty-five divided by sixty-five two.

It gave, two zero point sixteen watts. Notice that it is a power that has absolutely nothing to do with that maxim, right? One hundred and twenty-five watts.

So if I have two point zero sixteen for him to work with clearance without heatsink, I have to see if the current that I calculated, sorry for the power I calculated fits that limit there. Actually yes. Because I I calculated a power of zero point eighteen watts, very less than two watts.

Therefore, for this load of one ampere, on mosfet, I can work without heatsink, OK? Transistor without heatsink, because it is far from two watts of internal dissipation as a function of the calculation we made now it is? So, it is possible to use yes without heatsink, in case of a load of 1A.

Good people summarizing what is a transistor fundamental nowadays for many applications, we do not let's go into details here of using it as amplifier or DC or AC analysis of a MOSFET of a circuit, because they are extremely long and complex with many formulas. We'll can a second video, then entering in more detail in some application areas, OK? The as I already said, it can have this casing, but also can have a casing like this, look, a casing of one of lower power, it looks like a bipolar transistor, just like that one, right?

But is it an OK mosfet? We learn here so what it is a mosfet, what are its advantages, remembering that it has a very high gate impedance, so it can be used in different instrumentation areas. have a current also tending to zero here at the gate, because of this construction.

It is sensitive to static electricity, but because it has a diode, up to here in the datasheet there is a diode designed, protector, that greatly minimizes risk on the latest components, It has datasheet features, which you need to analyze before starting any project with it, That would be the VDS voltage, the drain-to-source resistance, the maximum drain current, the maximum power dissipated. The maximum junction temperature, among others, OK? The voltage also triggers, right?

threshold voltage, Here at the gate, okay? We saw a little about the characteristic curve his, his work areas, right? The cutting part ohmic linear and the saturation part, the use key as a key, among others.

good guys, I hope you liked it, click like if you liked the video, subscribe to the channel and see you in the next video. Much thank you, a big hug.