All right, let's have a look. Look at this portion of the slide right there. And this is a schematic symbol for diode, okay, and this right here is my cathode. All right, my cathode is right there. All right. Now, these are physical representations of diodes and I need to place them in a circuit appropriately so for instance, for this here to work correctly, I need to have my cathode pointing to the negative terminal the battery just like this, and if I hadn't said it, this was Call the anode all right here we go this is a better refer it's better than than my writing here it's I'm having a hard time I at some point I got to find something that's a little bit nicer to make letters it's it's it's not that easy to to write on this but I his mic his kids a graphical representation or a schematic symbol of a diode right there and his my anode right there here's my cathode right there this is p type material and type material and they say direction of current flow.

And I just want to make this perfectly clear that that really is it. When we say current flow, we can mean whole flow or electron flow, alright, that is current flow, but it's actually electrons being Because electrons flow against the arrow of the battery, and like I show you here, they flow up through the diode and into the positive terminal of the battery. So that is current. When they say current flow here, it's actually electron flow. Okay, here are my elements here. Notice we have my anode lead again my cathode.

And we have some identifying mark on the physical body of the diode component, as seen here. So here I got a negative here, I got like a little bezel, Ah, here we go to Plus, there's a reason for that is saying, well, you're not sale. Well. You're saying that no, no, I'll explain why they put a plus there in a couple of slides above. And I'll say you remember back at this slide I showed you put a plus there is the reason. All right, notice it's a we've got three stripe closest to one and that's the cathode metal case, right there.

And then this one is kind of neat because it actually puts a, a symbol of the diode on the body of the components. So you can see. All right. So when when you when you want to place a diode in this circuit, you need to observe, which is the cathode, which is the anode. And you need to place that in the circuit correctly for the circuit to operate the way it was designed. And that's pretty much it here.

All right. So let me clear the slide off and I'm going to the next slide. All right, on this slide here, we've, we've kind of covered this before in previous I think it was slide but I just wanted to go through it one more time. And make sure you want to stand and it's gonna be like, a little bit of something new. And then then something of a review. Okay, so now here's my circuit.

Okay, I close the switch. I know I'm going to conduct current, because this is what this is my and Oh. And this is my cafo. Okay. And we know from previous discussions that electron flow wants to flow through our against the arrow of the diode. So I know that my diode is in the circuit properly.

I'm going to conduct current and what am I going to do? I'm going to light the lamp which is what I want. When I close that circuit. Everything's wonderful. It's working. All right.

But what if I want to know what the diode drop is across the diode and again, This is a review. Well, I can use this formula here where ID is the current across the diode, which is vs, which is my supply voltage minus DD. And DD is the voltage drop across the diode divided by the resistance in the circuit. It's just it basically it's also off. All right, in this example, the resistance in the circuit is 1000 ohms. All right, and now I go through my math and if I've got a silicon diode and a silicon has a forward voltage drop of point six volts and a germanium diode has a volt forward voltage drop of point three volts.

And if you remember, back at the very, very beginning of this course So I had a slide up there, I think it's the second or third slide in the sequence, which shows you the turn on voltage for germanium and diodes. And again, it's point three for germanium, point six for diodes. And it also showed us the reverse current. So if I turn my voltage source opposite how much voltage I could put across that element before it would break down. All right, so go look at that if if you're if you don't remember that, but anyways, so now I can find the current. So if it's silicon, it's gonna, it's going to be six volts minus point six volts which is the diode drop divided by 100 ohm resistor.

I do my math, I get 5.4 ohms. germanium, same deal. The only difference is on a germanium diode. My forward voltage drop is point three volts. I do my math and I get Point 5.7 milliamp hours, there's about 300 or micro ampere. So point three milliamp hours difference between the two.

All right. And and basically that's how I find it. Now I just, I just wanted to put that out up here. Make sure it was clear. I believe it to be clear. All right.

But before I go on here, let me stop and I just want to make some some point here. Okay, right here, it was showing what vs is what? six volts, right? Right, I kind of I kind of showed it to you down here v s is six volts. All right, we go through the math and we subtract point six and we subtract point three. Okay, that's fine.

But what happens if my supply voltage is 60 volts, or 600 volts? Do you think I really really need to take that diode drop into consideration Well, probably not, because if it's 60 volts 60 volts is what? 100 times greater than point six volts. All right. And 600 volts is 1000 times greater than the voltage drop. So you think maybe my era with current might go down.

Yeah, if I'm 600 volts, and I do it, I got six tenths of a volt. Okay, well, what is what is that going to be? A couple of micro hampers. So the point I'm trying to get to here is the same deal that I kind of spoke to you with a couple of slides back. Okay, putting components together. Okay, you remember what I said?

I said something like, okay, you know, what, if it's hot What if it's cold? Is this gonna work? And one of the things that I also mentioned about that is if it's comfortable for you, the circuit is going to work. Alright? So when I do my calculations, or I look at my current flow, my voltage drop or whatever, I need to look at the whole thing. All right?

The whole picture. I mean, basically, practical engineers. If I've got 60 or 600 volt, voltage source on a circuit, I'm using one or two diodes, would I really, really, really want to put a point six 0.3 to get down to that nitty gritty current? If I'm a practical engineer, probably not. I you know what I'm saying. So, again, look at it.

And again, now I'm getting anal again. Look at it, see what you're doing, and get a feel for things. All right. Nuff said. gonna clear the slide off. We're gonna go on Alright, We can we can test a diode with a, an ohm meter, what I'm showing you here.

And again, if you remember this, it was in one of the other slides is my anode is my cathode. All right, so my foot four with a no meter to correctly forward bias this diode. All right, I would put my black meter lead on the cathode and my red meter lead on the anode. And I would get current flow through the diode from the meter. Now, some of the well I shouldn't say new, I'm showing my age but the meters today have what they call a diode, okay scale or a diode scale. And it's, it's on the meter.

It may not be exactly where that is, but Because they may be listed as shown somewhere differently on different meter manufacturers but you would have that on the diode scale and you would test the diode. And then if I swap my leads or swap my diode notice that my cathode is there and up here my cathode was here. Pierre I'm my cathode is with my black meter lead up here, it's with my red meter lead which is plus, okay, now I would get higher resistance, because there would be no current flow because I reverse bias the diode. Alright, so with that said, that's how I measure a diode. One of the things I want to add the diode to.to test a diode properly, it needs to be out of circle. And you can kind of test the diode in circuit, if you know what's attached to it because the components there will act as if they're in parallel.

So one of the things that that that I used to do if I was troubleshooting is instead of taking the whole thing out of the circuit, you can just lift one one leg, make sure the power is off, of course, just lift one leg out of the circuit and put your meter lead across appropriately and check the diode and see if these conditions work out properly. All right. Now, let me ask you this. What happens if I measure my if I measure a diode and I do this and this but I get high resistance in both directions. That diode is bad and the diode is open. Same thing is if I swap My Media leads in both directions and I, I keep getting something like that, that means that diode is shot it in either case what the diode is broke, the diode is not functioning properly, the diode needs to be replaced.

Now, your job is to make sure that something in the circuit that this diode is placed in is not causing that malfunction. So, I'm not going to address that now, only because we haven't built the foundation enough we're building the foundation By the way, but not enough. All right. So when we get a little bit more into circuits, if we could diode I'll kind of expand upon that but One of the things, again, I'm throwing some stuff out here for you guys to think about. One of the things that you need to think about is when a component goes bad. Did the component go bad?

Because of age or just plain? what I call electrical stress over the year for the circuit being turned on and just normal operating conditions? Or if it's a new design? Did I design the circuit properly, and maybe I'm stressing that component. Alright, or did something else go funky in the circuit that blew this diode up and maybe I've got another bad component in there somewhere. So we need to look at we need to look at some of these things later.

And to see why okay, because quite honestly, maybe I could maybe I'd replaced this diode in the circuit, and it would go plus it'll break again. So when You're going to do keep putting diodes in there. No, that's not the net. There's something else going on. Alright, Nuff said, Get an angel again, see in the next slide. All right, let's, let's look at this little circuit a block diagram.

And again, I'm not going into the nuts and bolts, I'm just trying to give you an application a little bit of background here of what we can, some of the things that that we can do with a diode or diodes, and obviously, I've got a battery. Okay, and let's say that that battery has a 12 volt voltage, alright, and we've got some type of load even though I'm showing a resistor, it doesn't have to be a resistor. From here to here. It could be a box with electronic components of some sorts, but we're showing you notice it says resistor load I and I want to kind of keep the voltage here at 12 volts maybe, maybe give it Take maybe, you know, half a volt so so we have a nominal voltage of 12 volts. And let's say because of this circuit, I wanna, I want to keep my my voltage in a narrow range, let's say 12 volts plus a minus a volt in both directions.

So I would go, high limit would be 12.5. Low limit would be 11.5. All right. So let's say I get I build a circuit called voltage monitor here. And what I'm going to do with this is I'm going to I am going to monitor my battery voltage across the load, all right, and then let's put some, some control. Whoops, let's go here in there.

All right, so what do we got here? So I met so I, I monitor my voltage now we have a criteria of a high limit of 12.5 and a low limit of 11.544. So this this, my my electronics, my load is funky, okay. It doesn't want to go below 11.5 volts. Alright, so now I put this I designed this voltage monitoring circuit and I attach it to my charging voltage. So let's see what happens all right.

So I can I can calculate a say okay when my voltage goes Have a tad low. just a tad now of 11.5 volts. I'm going to kick this on. And when I kick that on, all right, my charging voltage is going to be enabled. And I'm going to make sure that's more plus i, then this terminal here, all right. And I'm going to charge that battery.

Okay, I'm going to start slowly sourcing current into that battery. And the only way that I can source current into that battery is my charging voltage here has to be higher than my terminal voltage. Well, if I'm monitoring my voltage, my low end is going to be 11.5. If that's a silicon voltage drop what's what's my charging? And you're going to be that it's actually going to be about 13.1. Ideally, it's a lot higher than that sometimes, but 13.1 so now I turn my charging voltage on current will only conduct current one way.

Alright, it's actually electron flow is going this way. So notice that's my positive terminal of the battery. I have an excess of electrons there. So I'm taking electrons out of there and I'm charging the battery up. Okay? So I'm charging it up charging it up, charging it up, charging it up.

What happens when my voltage gets to be 12.5 volts. I turn my charging voltage generator off. I stopped charging the battery. All right. The only path for electron flow from the battery is this way through the resistor. And and again, this is a very simple circuit, I'm just giving you an idea.

All right. So what we have here is, all we have is a diode with some charging with some charging voltage, a circuit that that produces charging voltage. I have some type of circuit over there that monitors it, and I turn my charging voltage on and off, my diode is there to make sure that when my charging voltage is off, the only current flow from the battery is through my resistor load there. That's it. simple circuit. Just wanted to give it to you.

Just to think just to hopefully make some things light up. All right. Well, we're going to talk about some other things how to rectify as in that in a couple of slides. But that that's pretty much it. So with that said, I'm going to clear off the slide. We're going to go on to the next one.