Okay, we're going to talk about transistors, specifically junction transistors. And we have two types of junction transistors. We have a transistor that is a, p and p and one that's an n p n. All right, the this three elements of the transistor and they are common to both of them. We have an emitter. We have a base. We have a collector.

All right. All right, same thing over here on my NPN. We have a base. We have an emitter and we have a collector Okay. Now, there are two junctions. Now, if you remember from our our previous section, when we spoke about diodes, there was one junction there was a p n and n r All right.

Well, now we have two junctions, we have on a PNP we have n type material in the middle and on an NPN we have p type material also in the middle of the center All right. Now, we have where my emitter and base junction needs to be forward bias. We call that VBE. And if you can see, with this voltage source here, I forward bias that the junction over here, we have an NPN and this junction here is also forward biased right there. All right, so I'm telling you right here on a junction transistor, the emitter base junction must be forward bias meaning there must be an electron flow. Okay.

Now we have another junction we have the collector base actually let me stop and clear the slide off. Okay, now we have the other junction which is the collector base junction right here. And as you can see, we have a battery and we call that V I'm sorry we call that V cb. voltage from collector to base. This one's a little bit wrong flip, but it's okay. All right, and that is reverse bias.

Okay? Same thing over here. reverse bias, okay? Now that's what I put here collector base junction, reverse bias, okay. All right. Let me stop and clear the slide off here.

Okay. Now we have two schematic symbols. You can tell the difference by the symbolic representation here, okay? All right, so here if I'm looking at the base Okay, my arrow is pointing in. P in You can think of it that way, p NP p in and if I look over here where it's an NPN I my Arrowhead is reversed and p n and p and p and p, p and p. So, schematically I can tell the difference by the arrow on my on the leg of the emitter. Right here, the leg of the emitter will tell me which way that arrow is pointing will tell me if it's a PNP or an NPN.

Okay, now I'm gonna I'm gonna go over these a little bit more detail in a couple of slides, but I'm just going to introduce these equations and they're both the same depending on if I'm using an NPN or PNP All right, ie equals IB plus IC, that means the amount of current is the summation of the current or electronic should say electron flow that flows in both the collector and the base. Same thing over here. All right, I equals IB plus IC, current flow in the base plus current flow or electron flow I should keep I need to use current flow electron flow, okay equals IE. Current electron flow in the collector equals electron flow on the base or the emitter Minus IB. Same thing over here. Okay.

So basically, if you look at these two far formulas for current flow in this device, it holds true. Now, just so you'll know a transistor is a current or elect controlled current source. In other words, the amount of current that flows in the base will determine the amount of current that flows in the collector. And we can use different circuit configurations where we can, we can predict that pretty pretty nicely and you'll see what I mean As we go on here, all right. So, right now on this slide, what I want you to know is this number one the difference between an NPN and a PNP. Each transistor has its own two's voltage supplies, one has to be reverse bias and one has to be forward bias, the reverse bias voltage sources always in the collector base and the forward bias will always be on the base of jmeter on both of them.

You need to see the difference between and let me let me regress here, you need to see what the graphical representation will do between an NPN and a PNP. All right, the arrows in in which one the arrow is out in which One. Alright, so take a look at that. And that's, that's pretty much it. So that this is the first slide on junction transistors are also called bipolar, bipolar transistors. All right, let's stop here and go to the next slide.

Okay, um, when we design or if we troubleshoot or whatever we kind of need to know. You know, we have emitter base collector. All right, and we need to know where they are. So if I have a transistor, and these are usually plastic, notice I've got a little flat here. All right, it says emitter, collector base. All right, and this one here, still have a flat but we have emitter base collector, so they'll be in name on a transistor.

It'll be a two inch Something and basically what we'll do is we'll get the specification sheet. And this specification sheet will tell us you know where where which lead is what emitter, base, collector or so forth. But sometimes we can look at the packages. All right, if this is unique emitter collector base, but notice we got a little cutout here and that's always the collector. Over here, we're looking at the front of the transistor and its collector base emitter. Over here, my the physical layout of the transistor is square and we've got emitter base collector.

And I don't know how this one got in there. This is for a field effect transistor. We'll we'll skip that one right now. And then we've got different case styles. This is a to five Three to 18. All righty.

And these are pretty much standard right here. Notice I've got a little niche or a little tab EBC EBC EBC. And over here looking at the bottom, that's the case, notice that the emitter and the base leads are skewed a little bit they're they're off to one center. But the best thing to do is if you're unsure is when you get when when you're working with a transistor or transistors. And you need to look at the the actual mechanical or the physical layout of the transistor to know which means the base, collector and emitter in some manner. It's best to pull a spec sheet with the internet today, you could just go into the search bar and put transistor to end whatever And I mean it'll pop up or you could go to some Digi key, there's James electronics, just to mention a few.

They'll have that they'll have that. So that should be very, very easy to find the, the, the mechanical layout of the transistor and I suggest that you do that. Just to make sure that when you're troubleshooting the circuit that the lead that you believe is the emitter is indeed the emitter. Alright, with that said, I just want to look over here on this, this part of the slide. And we talked about on the previous slide, we talked about junction the junctions are the transistors and they like a transistor is like two diodes back to back. All right.

So we can say we have a P and P If we're thinking of it in terms of diodes, that's how my transistor would look like. And if it's an NPN, that's how my transistor would look like cathode, anode, cathode. And the reason I'm doing this, you'll see on the next slide, I'm going to show you how to test a transistor. Alright, so let's clear the slide and go off to the next one. Okay, what I want to show you here is how to up how to test a transistor. Now we're going to use an ohm meter and I know that they have transistor testers out there where you can point the whole transistor in there and you get a either a green or a red light or go and no go.

Well, I think I bought one once, but primarily I've always used an ohm meter and it's it's really easy So, right now we have a n pn transistor and if you remember what I said trends of transistor is like two diodes back to back. So, notice this is the red lead we put and I mean you can start any way you want I just picked this. So, I put my red meter lead on the collector, my base my black meter lead goes on the base and I should forward a bias that junction right and I should get low resistance. Okay, so now what I do is I leave my lead on the bass and this is and once you get get the act of this, you can do it any way you want. But I would leave my lead on the bass and then I would go to my emitter here.

And again, that should be low resistance. Okay. Because I forward junction that that I'm following the junction that that part of the transistor, the base emitter, okay, so that will be good. Now, what we did notice that I swapped My Media lead around. So now I've got my red meter lead in there. And what have I done with the base emitter now I've reversed bias it and therefore I have a high resistance.

Take my black media lead here, bring it over here, still reverse bias that junction, high resistance. Alright, then what I've done is I've taken my media leads and I've gone across the emitter, collector, and I should read high resistance. And then what I've done is I've swapped the leads. This In other words, this was my product. have now it's negative and I brought my positive media lead over there and again I should get high resistance transistors good if it if it follows this where I show you high resistance high resistance and at some point low resistance if it follows this sequence the transistors Good. Now, if if for instance if I'm over here and I get low resistance then my emitter collector is shorted and transistors bad All right.

So, if I stray from this where everything is high resistance and the transistor is open and if I get a low resistance where I should have gotten a high resistance path than that junction or that part of the transistor is shorted That's just pretty much it. All right, so I'm going to stop here, we're going to go to the next one here, I did a PNP. On the next slide, I'm going to do an NPN, which is basically the same deal, I'm just going to go over it, it's just that my lead my polarity on my leads are going to give me different results. So let's stop here and go to the next one. All right, on this slide, if you really look at it, it's the same. All right.

The only difference is the readings are going to be opposite. So for instance, on the other one I had low resistance now I have high resistance because when it's an n, p n, right now this junction is reverse bias or get high resistance. And the same thing over here. I'll get high resistance. All right now I swapped My Media lead, and I put my plus on my base, which is the middle. And now I'm forward biasing the junction.

So I get low resistance, low resistance. All right, but notice these reading stay the same, okay? Ideally, if the transistor is good, all right, then I should get high resistance between the emitter and the collector of the transistor. Alright, so take a look at that and I'm going to erase this slide we're going to go on Okay, on this slide here, I give you two schematic symbols of a transistor, a PNP and an NPN. And I define their elements collector base. And emitter.

All right, well again when I say PNP and ones in NPN Okay, that's now we're going to define what not what current flow is. We're going to define electron sorry electron flow and the the electron flow through the base element is IB okay. electron flow through the collector element is IC emitter element IE and I introduced this equation at the very beginning IE which means the electron flow through the emitter equals the electron flow through the current collector plus the base. So we can say that I II has 100% of the electron flow. I see has about 98% in IB has 2%. All right, approximately.

All right. And let me clear the slide off and show you how electrons flow even though I say current flow here, I'm going to describe electron flow. So and again, if you've taken my other courses, you know that current flow is either electron flow or whole flow, depending upon which we use. And in my courses, I use electron flow. So let's, let's stop here. Let me clear off the slide and we're going to talk about that.

Okay, so let's look let's look at the PNP first. And what do I have I've got my bass current flowing this way All right, that's my bass current. And if you remember I've raised it but bass current was what 2% and now I have my collector current or electron flow flowing and it flows down and it combines with my base current flowing through the emitter. So you can see that the emitter current or electron flow in a PNP transistor. Now you can see here that when I've got an NPN I'm sorry a PNP transistor, I get electron flow and all of my electron flow flows through the emitter And the same thing with my NPN. Let me just do that real quick.

All right, so we've got go this way against the outro loop. And we go through here. And then we go up this way. That's an NPN. So let me just do this here. All right, on this here, we've got electron flow This way, this way, and on this one here, this way and this way But both on both transistors PNP and NPN everything flows through my emitter element and that's what I have here right there, alright.

Now, we have an amplification factor called beta and every transistor, the manufacturer will supply a beta and that beta, unfortunately, depending upon the transistor can be a window from like 50 to 100 or 30 to 60. All right, if I want a more specific beta, then the transistor well will cost a little bit more because it's more precise, but primarily we use you know for general purpose Applications of transistors may have a beta of 50 to 100 or something like that. And then with the circuitry that we, we implement, we can, we can get a more of a precision on it and get out a finite gain, which I'm not going to go into here right now, even in this module that that is when I do amplifiers, that type of thing with transistors. We'll, we'll get into that a little bit more. But the only thing I really want you to know now here is that beta is the amplification factor.

And we know that I see which is the current flow through the collector equals the current flow through the base times the beta of the transistor. So therefore, if my beta has a window, then maybe I collected current will also have a window. All right. And then one more. One more spec that I want to give you is called the alpha. You can think the alpha as the quality of the transistor.

It's icy over IE, I, ideally we want that to approach to one. And that would be that I see would equal IE, but that's not going to happen. So, alphas are usually with today I usually around 97 to like 99. All right, and that's just the collector current divided by the current or electron flow and I apologize. I keep saying current when I say current, I'm really talking about electron flow or the convention of electron flow. Alright, so that's that's what, that's what that is.

And there isn't much more I can say here. So what do I want you to get out of this slide? Well, I want you to get out. Again, what I be is, what I see is and what I eat is and how they flow through both a PNP and npn transistor, I want you to know that I equals IC plus IB and know what I mean by that. Know what we mean by beta and know what we mean by alpha. Again, beta is an amplification factor.

Alpha is the quality of the transistor ideally. Ideally, I, I really don't want to waste any current on the input. But that's not going to happen because we don't live in a perfect world. So ideally, we want to approach one but would never going to get there. Alright, Nuff said on this one. Let's go to the next slide.