TechStuff Tidbits: What is a diode?

if you're not familiar with electronics, you've heard the term diodes. Heck, l e ED. That's a light emitting diode. You have lots of stuff all around you that has diodes in it. So it's easiest to explain diodes by starting with the kind of of function they fill within electronics. So a die ode is sort of like a check valve in a plumbing system. So a check valve in a in a pipe, for example, will open when water flows in

one direction. The water will push against the valve and the valve will lift up and water can flow through. But if the water starts to come back in the opposite direction, then the water is going to push the valve cap back down and the valve will close and the water can't keep going. So this way you can allow water to flow one way through the pipe, but it can't come back, which is important in some types of you know, hydraulic systems, that sort of stuff. So

diodes do something similar. They allow electricity to flow in one direction in a circuit, but they prevent it from going the opposite way. Now, a quick word on that. When we talk about current and flow, things get a little confused due to the fact that electrical engineers described current as moving from positive to negative. But if we look at the at current as the flow of electrons, we know that this is the opposite of what actually happens.

It doesn't go positive to negative. Electrons move from negative to positive. This is because electrons themselves have a negative charge, which means they're repelled by other negative charges, right like repels like, and opposites attract, So electrons are attracted to positive charges. So if you've got a big old bunch of electrons crammed in together somewhere, they're all desperately trying to get away from each other. But if you then create a pathway where electrons can travel to a place

where there's a positive vibe. They're gonna rush through that pathway to get to the positive place because no one wants to hang out at a party where everyone as negative all the time, So they're so eager to get over to the positive place. You could even make them do work along the way. This is the basis of electronics. That electrons move from negative to positive, and along the way you can make them do work because they just

want to get to that positive place. Man, they will do whatever it is they need doing, assuming they've got enough behind them to get the job done. Now that's a pretty clumsy analogy, but it does fit anyway. There are a lot of electrical engineering textbooks that talk about what we would call conventional current. Conventional current is the positive to negative flow. This is how Ben Franklin would

have talked about it. Uh And unfortunately that's just not what's happening on a on an actual physics level, but on an electrical engineering level. You can often see diagrams that will depict current as flowing positive to negative. So if you ever come across descriptions that talk about current this way, it's from an electrical engineering perspective. And by

the way, this does have its uses. It's not that this is this is to a point where it's going to mess you up unless you're looking at a diagram and you're making, uh, the opposite assumption based on the diagram. Instead, it's useful for talking about specific systems. So I don't mean to completely dismiss it, but it is kind of funny to me. But I am going to talk more about the electron flow description of current, So that means

going negative to positive, because that's what's actually happening. If you were able to somehow visualize the electrons as they move through the system, that's how it would go. All right, let's get back to diodes. So let's say you're putting together a simple circuit with a diode and you've got a light bulb connected, and then you're going to connect

a power source of battery. Now, because diodes only allow current to flow in one direction, if you've installed the diode the wrong way around, it will actually prevent electricity from moving through the circuit and the bulb won't light up. If you flip the diode around, then it allows the electricity to flow through the circuit and the light bulb comes on. So when the diode faces one way, it's behaving like an insulator. It's it's preventing the flow of electrons.

If you flip it around, it acts like a conductor. It conducts the flow of electrons um And it turns out the yeah, diode is a semiconductor component. It can act as both a conductor or an insulator depending upon the situation. A diode positioned to allow current to flow is what we call in the forward bias. Forward means that electricity can flow through the diode. If it is positioned to act as an insulator, it is in the reverse bias. It will prevent electricity from flowing in that direction.

But how like, what is it about a diode that allows this to happen. Well, that requires a bit of physics, alright. So a conductive material has a lot of what we would call free electrons, meaning these are electrons that are not in fully packed electron shells. They can be boosted out with just a little bit of energy and then

be free roaming electrons. But uh that so you just have to add some energy, right and then once you do, then the electrons will start to move through the material and they will be moving towards the most positive area

connected to this material. And then if you have an insulator, while you've got electrons that are very tightly packed, right, there's no movement available, like there's no room in the end, so there's no place for an incoming electron to go, and it kind of just bounces off and you know, it acts almost like a force field. Now, to make a semiconductor really useful, we actually have to dope it because semiconductive material has fairly tightly packed UH atoms and

fairly tightly packed electrons. So without doping it, without introducing impurities, then you're not gonna be able to easily make it conduct It will act as more of an insulator than a conductor. So we're just introducing something else in there to change up the structure really and you can actually dope semiconductor material in one of two ways. You can dope it with atoms that actually have extra electrons in their outermost shell, which creates an in type semiconductor or

negative side. Or you could pack in atoms of stuff that have fewer electrons in their outer shell, which means we they have holes, they have places where electrons could occupy. This is p type semiconductor material. Now, let's talk about silicon to give an example. So a silicon atom has four electrons in its outermost electron shell, but it's an electron shell that can accommodate up to eight electrons. It's just that silicon doesn't have eight and its outermost as four.

But if you get a lot of silicon atoms together and they form covalent bonds with one another, then each silicon atom is going to bond with four other silicon atoms and they're gonna share outer most electrons, so that each atom, if you were to look at it and just kind of ignore the fact that there are atoms around it, it it would appear that there are eight electrons and net outer most shell and then would be all

full up. So, in other words, when silicons all together as a as a material, as opposed to a single atom, then it's acting like it's got full electron shells and its outermost shell. So what you want to do is introduced something else, like phosphorus, which has five electrons in its outermost shell. So silicon has four, phosphorus has five. If you start putting phosphorus, if you dope phosphorus into silicon. Then these silicon atoms, some of them are bonding with phosphorus.

But that means there's this extra electron that has nowhere to go, right, because you only have enough room for four of those electrons in that oldermost shell to bond with other atoms. The fifth one is kind of loose on its own. So now you have electrons that could easily freely move through this material. Then, if you want to make a P type semiconductor, you dope silicon with atoms that have fewer than four electrons in their outermost shells.

For example, aluminum as three. So aluminum bonding with silicon means there's gonna be an extra space for an electron. You get a hole there. Uh, And so you have this N type or negative semiconductor material that has an excess of electrons and thus has a negative charge. And then you have a P type semiconductor material that has an excess of electron holes, and we describe this as having a positive charge. So if we put IN type

against P type, we create a diode. So you have N type semiconductor material on one side and P type semiconductor material on the other side, and where the two meet is called the P n junction. We'll describe its function after this quick break. Okay, so we have the P n junction where the P type semiconductor material comes

into contact with the N type of semiconductor material. What happens then, Well, if you remember, the N type semiconductor or the N type side of the diode has an excess of electrons, the P type has an excess of electron holes. So you would think, oh, well, then all the electrons are just gonna move, all the free electrons anyway, the excess ones are going to move from the N type side to the P type side, and it'll just

equalize out. That's not exactly what happens. What does happen is some of the electrons do move over from N type to P type, some of the holes move from P type to N type, and it creates what is called a depletion zone at the P N junction. It creates this electric field, and that electric field has a charge there that prevents more electrons from N type to move over to the P type side. So it's like

there's this this force field. It's a weak force field, but it exists, and in order to get through it, you have to add more energy to the system. But without that added energy, the electrons just can't make the jump. If you think about it, it's kind of like let's say you're well, you're a kid, and you're running around in the woods and you come up on an old like little dry creek bed that's created a ditch, and the ditch is not wide, but it's not super wide.

If you get a running start, you can jump over that ditch. But if you were to try and jump just from a standstill, you never make it right. You'd fall into the ditch. You have to have enough energy to make it all the way across. That's the same way with these diodes. Without that energy, the electrons aren't going anywhere. They are essentially blocked by the depletion zone

and the electric field that it creates. All right, So then if we then attach the P type side of the diode, the annode side, to the paw stive end of the battery, and then we take the cathode side of the diode on the N type and we attach that to the negative side of the battery. Well, now the battery is providing enough voltage, enough pressure, enough energy to push those electrons from the inside over to the PA side, and then they continue they're attracted to the

anode because the anode is positively charged. Now that it's connected to the positive terminal of a battery, and you get the flow of electricity, And as long as the battery is still attached, it's going to continue to provide that voltage that will allow the current to continue to flow. So electric electrons will continue to go into the N type side and push over to the P type side and then continue their journey over to the positive terminal

of the battery. And it'll do this till the battery runs out of a charge or essentially doesn't have enough voltage enough energy to push those electrons over the depletion zone. But then what happens if you turn the battery around, right? What if you what if you put the battery in backward, Well, now you're gonna have these opposite charges. You're gonna have a positive charge over at the cathode side, over at

IN type side of the diode. You're gonna have a negative charge over at the anode side, over the P type side of the diode. And that negative charge on the anode is going to attract all the holes over to that side. The positive side over at the cathode is going to attract all the electrons to that side. The middle of your diode is going to become a much larger depletion zone. So in other words, there is now a much larger barrier that you have to jump.

It's like that ditch that you came across in the woods has turned into the Grand Canyon. You are just not gonna make it across that ditch no matter how fast you run, except with diodes it's not quite the same. So with diodes, you can create enough voltage to jump that barrier. The problem is when you do this, then you kill the diode and potentially you fry whatever circuit it was connected to because you've you've added enough voltage

to overcome this depletion zone. But for normal operation, that depletion zone is enough to prevent current from flowing. So that's why we say diodes are kind of like a

check valve. I guess in a way, you can think of it as a check valve in a pipe where you have just put so much water pressure that it breaks the check valve inside the pipe at the pipe itself, possibly might break two and that would be very similar to what we're talking about in circuitry, where a diode has had enough Essentially negative voltage is what it comes down to, because you're you're talking about a reverse bias

in this point up to break through that depletion zone. Okay, that's generally what how diodes work, right that they are kind of a one way lane for electricity. But what do we actually use them for. So in some ways we use it exactly as I mentioned, like a way to control the way electricity can flow, but we also use them for other stuff like light emitting diodes. Obviously emit light, they are l e ed s. We use these in everything from light strips to ultra high definition televisions,

but we also use diodes to do other things. So one examples, you can use it as a rectifier. So a rectifier is something that allows you to convert alternating current into direct current. So direct current is easy, right, you have current that flows in one direction. This is what batteries do. It goes from the negative terminal into the positive terminal. That's it. It cannot go the other way.

It's not going to go from the positive terminal to the negative terminal unless we're talking about conventional current, which we're not. So so it's that's direct current. It's always going to go in that direction, and most of our electronics run on direct current. Alternating current reverses the current direction many times a second. We describe them and hurts.

So if it's like a hundred and twenty hurts current, that means a hundred twenty times a second the direction of current is switching, going one way and then the other way. It does this add twenty times a second. Now, getting into why it does this would get into more than what the scope of this episode is about. But this is what we use in order to transmit electricity great distances because alternating current can make use of something called transformers, which are more than meets the eye, but

they're not robots in disguise. No transformers are used to change the voltage of alternating current, and stepping up the voltage or increasing the pressure if you will, means you can push the electricity further down power lines and then you would step down the voltage. You would decrease the voltage when you were ready to transmit electricity from the

power lines. To say a home or a business. But we still have to be able to change the alternating current into direct current so that our actual electronics can make use of it, and a diode can do that because a diode will only allow current to flow in one direction, So essentially it would only allow a C current to flow through half the time when the direction of the A C current matches the direction the forward

direction of the diode. The other half of the time, it would block electricity from from flowing because it's against the diode. Now, this would mean that you would have a pulsing direct current. So you could actually use collections of diodes and some other components to make this a more smooth operation, including enough diode so that whether the electricity is traveling in one direction or the other, the diodes create a pathway that allow the electronics to make

use of direct current. It's pretty cool. It's very difficult to describe without the use of visual aids, but yeah, diodes are incredibly important for that. We can also use diodes with radio waves. Again, a deep discussion of radio waves is beyond this, but you know you can encode audio onto radio waves. That's how radios work. If you tune into a radio station, you know the sound has been encoded onto radio waves. We use diodes to extract the audio from the carrier signal of the radio wave.

So yeah, they're really important components and I hope you have a greater appreciation of them. And uh yeah, that wraps up this tech stuff tidbits. I'll talk to you again really soon. Y tech stuff is an I Heart Radio production. For more podcasts from my heart ray you visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H