Okay, let's let's look at this here. Right now we're looking at the we're going to start looking at diodes you know understanding diodes and transistors, but right here this is a curve for a diode and we know that a diode will conduct current in only one direction. All right. So this these are what these two graphs are trying to tell us. Now, this graph here, all right is a resistor, okay, so if I've got a resistor and a circuit, as you know previously I've got current flow. So, if I have 100 ohm resistor and I have 50 milliamp hours of current flowing through that resistor.

That is going to create five volts or a five volt voltage drop across that resistor. All right, now if I increase my current or if current is increased by 100 milli ampere, still have that 100 ohm resistor, then the voltage across that resistor is going to be 10 volts, right? And what was showing this way basically was showing the same thing. All the The reason it's going this way, is because current is flowing in the opposite direction. All right, so if I've got a resistor, which is 100, ohms. All right, this hair this way here, up here, current would be flowing this way and when it goes the other way, counts falling that way.

So that that's it. That is That's a way for them to show that graphically, that's all. Alright. But over here now let me stop here. I'm going to clear the slide off. Okay, now we're looking at a diode and let's just let me just put a diode here.

This is schematic symbol for diode, I'm sure that I've got one further upwards done nicely. It's it's difficult to draw here with with this pen and this screen here, but just bear with that, okay. All right, so we know that we forward bias the diode, and we're going to go into this a little bit deeper in the next couple of slides. But currents going to flow this way. If electron flow just so you'll know flows against the arrowhead. That's my Arrowhead.

But the point I'm trying to convey here is if you remember at the very, very last slide, we had Let me stop here and show you. Okay, and this one here. Do you remember that formula? Okay, current flu the diode, well, that still holds true to that. Okay? Because all the silicon here is is represented by that schematic symbol of a diode.

All right. So now if I look at that it's, if I want to find the current flow, it's six volts because I have a six volt battery, minus point six tenths of a volt, which is the voltage drop across a silicon diode. All right, and then I go through my math and I get 5.4 milliamp hours. Hold that thought we're going back to the next slide. Okay, so what this means here in this part of the curve, do you see how we have Vf? That's voltage forward And what we mean by voltage forward on that, on that graph is we have placed a voltage across the diode to conduct.

The majority carriers are electron cloud. All right? And this knee, right there is the turn on point, which would be six tenths of a volt. All right. And it's, I mean, it's not linear linear. I mean, it's ideally if it was 100% linear, it should be a straight line like that.

No, it there is a little bit of sway to that. And let me clear this and show you what I mean. There is a little bit of sway ideally, this should go off here, so it's not 100% linear. If that was 100 percent linear, it would be like that. So what we can say here? Okay, well we do our calculations for current and that type of thing, we can say six tenths of a volt.

But as current increases, all right, and that current flows through the diode, then I actually that six tenths of a volt is going to increase, but it's not going to be that much. All right. And quite honestly, we're not going to do it now, but at some point, maybe not in this course. But in another course we're going to look at at a diode specification sheet. And one of the properties of of any semiconductor I don't care if it's a diode, a transistor, I need a graded circuit and so forth, is going to be a value for nominal current. And there's going to be a value for maximum current, okay, so, if this diode here has a maximum current of, let's say, one AP, and I start increasing the voltage or lowering the current and so forth.

And the current exceeds my maximum current what's going to happen? Yeah, something's gonna smoke and it's probably going to be the diode. And that curve is just, it's not gonna, it's not going to mean anything. All right. So even though what, again, what, where can we see this curve? All right?

There's, there's physical constraints. And that's with any component resistor, a diode, a transistor, a power supply a transformer, we have to know where we're placing these components. And we have to know the environment that we're in placing it in. And can this component that I'm placing into this environment, can it withstand that? All kinds of stresses All right. Now, what is VR me?

Okay, VR me reverse voltage i. So now when I, let's say I do this is my diode, alright, and somehow I reverse the voltage, so it's not conducting. And I'm kind of hesitant to do that because we're going to do it later in the next couple of slides. But what happens is, remember those minority carriers that we talked about in the last section, I, well, that's them right here and notice, very, very small, all right, but they do increase as my reverse voltage gets larger. Okay. And you'll notice I don't know if I mentioned this we have if and I are, okay, notice when I forward bias the diode and put it in its conduction mode, I can have a large for current but when I Take the diode and reverse voltage on it where it's not conducting reverse current, I get a very small portion right there.

Alright. So, electrons flow through a resistor is linear, as we showed you here, diode conduction starts a few tenths of a second, which is right here. It actually starts when the voltage across this diode approaches point six volts and gets a bit greater, and then it starts conducting. And again, it's not linear there is like I showed you here there is some slope. All right, but that's good enough. diodes are wonderful.

I've used them use many many of them and they They really have a place place in our electronics world. So with that said I'm going to clear the slide off and we're going on to the next one, okay on the previous curve we we looked at a diode, characteristic curve of a diode okay there was one again from the previous slide we know right here is the turn on voltage okay. But we have two types of diodes, one diode which was on the last slide was made of silicon and then we have one type that was made from germanium. Now quite honestly the germanium diode was the first one the first semiconductor diode and then they came up with the silicon and they both work the same way. They both allow current to only flow in one direction, okay, electron flow. gets the arrow head right remember.

So electron flow is against the arrow head. And from the previous slide we know that my turn on voltage for a silicon diode is zero dot six volts. I, let me stop here clear the slide off. And for a germanium diode it's point three volts. And everything that we said in the previous slide about forward current and forward voltage is the same. The only difference is that for a silicon diode my knee or my turn on voltage is right here point six.

And for a germanium diode, my turn on voltage is point three volts right there. And again, with both of them then then not a complete linear because this would go straight Up here like that. Alright, the point I'm trying to make is as current flow increases through the diode, the voltage across a diode will increase, point three, four germanium and point six for silicon is a nominal value, and that will increase as my current flow increases, not by much, maybe 100, millivolts, 200, millivolts, and so forth. But again, if you remember what I discussed in the last slide, as my current through the diode increases, each semiconductor device has a maximum current rating. So, if I exceed that poof, the codes gone. Alright, so, you have to take that into consideration and again, this is my full width voltage.

All right, and notice my forward voltage stays pretty much constant at point three for a germanium and a point six for a silicon. Alright, and here's my forward current through the diode, okay, that will increase again, this is only a graphical representation. There are physical limits to any semi conductor device, meaning reverse voltage, the amount of voltage across it. The temperature rating, there are physical limits, so you just can't take again, I said it in the last slide, I'll say it again. You just can't take a semiconductor device and plunk it in somewhere and say, okay, it's going to work and in all environments, that may not necessarily be true. We were pretty safe if we do it in a in a environment where it's room temperature, the relative humidity Is is decent.

In other words, if you have a circuit, and you put it in environment and you're very, very comfortable in that environment, it's probably going to work. However, if you take a circuit and put it somewhere where maybe you're not that comfortable, you're going to have to look at the criteria for those elements for the circuit to see if it'll function properly. Nuff said with that, all right, let me stop here. I'm going to clear the slide off and I'm going to talk about the other end here. Okay, on this side of the curve, all right, Oh, those quadrants. If you look, we have again, we've got something called IR which is a reverse current and something called vi which is reverse voltage.

Well, if I put my diode back here and if I have current flow that way Okay, whoops, let me get that over there. All right, that's in my, that's, I'm forward biasing the diode. So that means and I'm just going to show you a battery here. It's not complete. So don't try to do it. We got minus there, okay?

And somehow let's put a resistor. All right? Okay, I have just forward bias that diode. But what happens now? If I change the polarity on that battery, okay, instead of being negative up here, it's it's plus, I'm going to reverse bias that diode. And that's what we're showing you here.

Okay. If it's silicon, if I reverse bias that diode and my via the voltage reverse voltage starts getting larger. In other words, this may be one volt it may be okay. Two volts, it may be okay. But what happens if I go 20 volts? All of a sudden?

Will that be okay? And let's assume that that's 20 volts there in the reverse bias direction. That diode is going to break down. And we're going to get current flow we're going to get current flow in a direction we don't want because why do we use diodes we use diodes. So current will only flow in one direction. So now what happened?

Well, I just blew the diode up that diode if I depending on what happens, it either can be an open in both directions, which means no current flow is going to flow in either direction, or I'm going to get a shot, which means it's going to act like a piece of wire. So be careful you have to look At att, again, the environment you're putting these things in, and you have to look at the spec sheet. So we'll look at some spec sheets later. Probably not in this course when we go into design some power supplies, and some amplifiers. We'll look at spec sheets a little closer, just kind of introducing it here and making you aware of it. Okay, so here's my silicon diode.

And if you look, okay, in my reverse direction, we hit some point and bingo, it takes off right here, we get a large amount of current flow, where if you look at my germanium diode, okay, yeah, I'd start stuff, kinda like breakdown here a leak, as a said, and that will continue it's in a germanium. It's not that nice curve. However, depending on the application of the circuit, we still have to be aware of that. And depending on if it's a germanium or a silicon when they exceed these points, circuits not going to work right? Is it? Alright, Nuff said.

I'm going to stop here. I'm going to clear the slide off. We're going to the next one. All right, looking at this slide here, I've put two simple circuits up here just to kind of give you an idea not an idea, but show you how electrons flow with a diode in the circuit I want to hammer this home. So, if I close this switch here, I and what did I say in the previous slides, we have electron flow that wants to flow against the arrow. So ideally, if this is forward biased and my circuit is Oh, is designed properly, I want to have electron flow flow against the arrow head.

So Will that work? Well, here's my negative sign here. All right, if you remember from my previous courses, I have a battery. And I have a surplus of electrons on this side and a shortage of electrons on that side. What does the electrons want to do? They want to equalize.

So all the electrons on the negative side want to go to the positive side. But let's look here. We have our diode. What did I tell you? An electron flow wants to flow against the arrow. It's going to try to go that way.

Is it gonna work? Nope. Not gonna. Okay, that's electron flow. It's going with the arrow. And basically what it is, is that elect that diode is going to act As an open, alright, no electrons are gonna flow so therefore my lamp is not going to light and that's kind of what I tell you here.

Okay? No electron, no electron in parentheses current flow, reverse bias diet diode lamp off, okay? So my lamp is off because my diode on this circuit here is reverse bias. Okay, let's stop, clear the slide off and we'll talk about the next one. Okay, now on this one, all I've done is I've flipped around the battery. Notice my negative terminal is right there.

My positive terminal is here. I close the switch again. What are the electrons want to do they want equalize. So they're going to calm and flow. Are they flowing against the arrow of the diode most certainly. They're gonna come and go to the positive terminal of the battery, I have completed this circuit, what's my lamp going to do my lamp is going to light on my lamp is going to be on.

That's it. So, a diode again will only conduct current in one direction. All right, electron flow again is against the arrow head against the arrow head. And depending upon how the circuit is designed, will determine how the current flow is and how electrons will flow if the diode is biased or turned on properly, okay, and that's what I tell you here. Now, just to kind of review something. If this let's clear the slide, I just want to drive some At home here, okay, if I look at this and let's say we're looking at this circuit here, I turn it on.

Let's say this is a, oh, I don't know, let's make this a six volt battery. All right? Okay, I get current flow, because my electrons are flowing against the arrowhead. What's the voltage across the diode? And we're going to assume that the diode is silicon. So that diode is going to have a voltage drop of zero dot six volts.

All right, and then we've got a resistor here. I didn't put a value there, but let's put a value let's put a value of 500 ohms. And let's say that this lamp when it lights has an internal resistance of five ohms And I want to know the current flow. Well, if you've taken some of the courses that I've done previously, you'll see that that's that's not a difficult thing. For one thing, it's a series circuit, because current flows in only one direction, right? And it has only one path.

So right here, both of these series, so what's, what's my, what's my current flow in this circuit? Well, it's going to be ohms law. Okay, we're looking for I so i equals what? v divided by R. So what's v well V is actually going to be six volts minus my diode drop, which is zero dot six volts minus zero dot six volts, okay. divided by the resistance of the circuit. So if if I even take into consideration this guy here, it's going to be 505 ohms.

All right, now I'll do the math in a minute. But basically that's it. Okay, so now I can get my calculator. And I'll figure out the current and that's the current flow through the circuit. But if I look at this circuit and I and I'll get that current a minute, okay, if I look at this circuit, and the lamp doesn't light the lamp doesn't light Why? What would what would I look at here if the lamp didn't light?

Well, let's let Okay, let me let me calculate the current and we'll get a stop a calculate the current we're going to talk about that. Okay, I calculated the current it's six volts minus point six volts divided by five right and five homes and when I do the math, I get 10 milliamps repeating decimal, I went to free places. It's 10 milliamp hours. All right, so we know that we've got 10 milliamp hours of current flowing in there. All right, so let's go back to that point I was trying to make. And let me stop here and clear the slide off again.

So now I close the switch. And I've designed this lamp supposed to light Well, jeek is the lamp doesn't light and wonder what's wrong. So how would I? How would I do that? Well, I mean, there's only a couple of things that we can check. Okay, we could take this lamp out, and we know that a lamp is a filament, right?

And we know that that's going to have some resistance so we could put a meter in here. Put an ohm meter. Alright, and measure the resistance of that lamp. Now if that lamp reads infinite then that's an open No currents got a flow lamp sock gonna come on. Okay. Another thing we can look at is the resistor.

All right, if you look at it, we calculated 10 milliamps as I said that was a 500 ohm resistor in the last last portion of this. So what happens if the lamp doesn't light? I see 500 ohms. Okay, oh, maybe the color code, maybe I misread the color code. All right, maybe it's not 500 ohms. Maybe it's 5 million ohms.

You think maybe if the value of that resistance was real high, like 5 million ohms. Maybe that might might have a problem because what happens is if the resistance on that circuit goes up, current goes down. Maybe there's not enough current to light that lamp. Alright, so maybe I need to check the resistor. Maybe check the color coding of the resistor and make sure that what i think i have is what's actually in here. Now I'm being a little bit anal with this.

Okay, I really am. But I'm what I'm trying to do is we're going to be talking about circuits. I'm trying to get chewed up the feel what's going on here. This is a very simple circuit. And anybody that knows electronics would have this fixed at about 15 seconds. All right, but I'm trying what I'm trying to do is get you to understand I'm trying to get your mind or your logic to go in a certain sequence.

So that when you get a larger circuit, you don't say, Oh, my God, I don't know what to do. So I'm trying to build that foundation here. That's what we're trying to do. So I'm going back to this resistor. I'm looking at the result. Well, maybe that's Maybe the resistors just plain bad.

I mean, I've had bad resistors usually, quite honestly, just we'll do it real quickly here. If if the resistor in the circuit has been stressed, in other words, it's been damaged by either he or another component in the circuit failed and allow that resistance to be failed or even sometimes I've had Miss mock resistors where the resistor was mocked, let's say 1000 ohms. And it was actually 1 million on the manufacturer screwed up okay. So, you got to be aware of that also. What can you do? Well, you can take an ohm meter.

And you can if what you would do is you would take an ohm meter is such This is such a simple circuit. I placed my own meter across the resistor, but I would make sure that I opened the switch here so it wasn't it Wasn't closed, and then I could measure the resistance of that resistor. And I mean and see if it's 500 ohms, because that's what it should be. Alright, that's another thing. The other thing is this, this diode could either be put in backwards, alright, right? Or it's open, it's broke, it doesn't work.

Or guess what the battery that you think is in properly as far as the polarities are written wrong. All right. So those are primarily the basic causes of why this wouldn't go, but one of the things that I can do one of the things that I can do is I can once I close this, since it is sir I can take an ohm meter nano meter, I can take a volt meter and I can go across each one of these components. One at a time or if I've got three meters or I've got a way to do it all together, I can do that. And quite honestly, if I'm measuring the supply voltage across any one of these elements, then there's something wrong with that element in this case, either either one of these, these three elements in there resistor, a lamp and a diode. Okay, resistor resistor, lamp diode, if I if I measured the whole supply voltage here across any one of those elements, and that element is, is open, and and then I would look at it a little closer.

But again, it's a very simple circuit. I'm just trying to get you to kind of get your focus in so we can troubleshoot and design okay. Alright, let's go. Let's just look at this top one here for a minute. Okay?