 Hi, today we will be learning about diodes. In a nutshell, diodes control the direction of electric current flow. Just like a one-way lane directs the flow of traffic by restricting it in one direction, diodes do restrict and control the direction of electric current flow in one singular direction. Now diodes like these are made out of semiconductors that power transistors and are found inside the device that you are watching this video on. Now multiple different types of diodes exist, all the way from Zener diodes to rectifier diodes to even LED's light emitting diodes that are found in our modern lights. Now we will be talking about the most basic general purpose signal diode for this video. Now like I mentioned before, think of diodes as a one-way lane for electricity. If we apply a positive voltage to the diode, it becomes a conductor of electricity and the technical term for this state is called forward biased. Conversely, if we apply a negative voltage to our diode, it will act like an insulator or like an open circuit. This state is called a reverse biased state. The circuit diagram symbols for diodes look something like this. Now as you can see there are only two terminals for the diode which makes it incredibly easy to wire. The flat side of the triangle that you can see here is called the anode and the pointy side of the triangle here is called the cathode. Looking at a physical diode, we can see a white line towards one terminal of the diode. This represents the cathode. Current flows in the direction of the triangle that means it flows from the anode to the cathode. But do note this is conventional current flow, not the actual electron flow of electricity. Let's quickly do a demo to understand how a diode can work. Okay so here we have our demo circuit. As you can see this is our load, we'll be using a simple LED. Now an LED is a light emitting diode so in this certain situation we don't need a diode but in case you use something else like a motor or some other electronic device then we would need a diode to make sure the current flows in the correct direction. Now we also have a resistor that suggests to limit the current because in our circuit we'll be using an LED but again the load or the electronics that we're driving can be substituted with the resistor and the load as per the electronics that you're trying to drive. The diode is here just to show the direction of the current. So as you can see in conventional flow the current will flow from the positive terminal to the negative terminal so it'll flow in this clockwise direction as you can see represented by these irons here. I stands for current that's the symbol for current. So let's go ahead and just do the quick test demo. Here I have an Arduino, here I have a diode, here I have a resistor and here I have my LED circuit here. So I'm going to wire it up and test it out. And as you can see as soon as we power it on the light turns on. Now if you flip the diode you'll see that the light will not stay on. So here's the diode I'm going to flip it around here and as you can see I've flipped it now I'm going to plug it back in and after plugging everything in the light is off and the real world diodes aren't perfect. In the forward bias position that means when they're conducting electricity they will incur a slight power loss because they aren't perfect conductors and have a little bit of internal resistance. Similarly in the reverse bias position that means when they're acting like insulators of electricity there will be a little bit of voltage leak because these again aren't perfect insulators. We can understand this behavior a little bit better using the voltage current relationship graph. Looking closely at this graph we can see a spike at the end of the reverse bias state in this graph. This is called a breakdown period and when too much negative voltage is applied the diode will break down and fail and become a regular conductor. This graph also shows us that the diode has something called a forward voltage. This is the bare minimum of positive voltage required for the diode to turn on and become a conductor. Lastly let's talk about some of the use cases of diodes. The first use case for diode is as a rectifier. Now rectifiers convert the common household AC voltage into DC voltage which is what most appliances use. By just using a simple diode we can cut out all the negative parts of the signal of an AC voltage and convert it into a DC voltage using a technique called half wave rectifying. Alternatively by using four diodes in this configuration here we can create something called full rectifier which converts AC voltage into DC voltage like this. Now the second use case of a diode is protecting against reverse current. Now imagine another appliance. You want to protect against the user installing the batteries upside down that means instead of installing the batteries positive or negative they install it the other way around from negative to positive. By adding a simple diode we can make sure that the electronic device doesn't get spoiled. In a similar manner the diode can also be used in a flyback diode configuration where a diode is attached to an electric motor so when you turn off the electric motor the electric motor doesn't turn into a generator and fry any of the electronics by providing a voltage back into your electronic main board. Thirdly diodes can be used to emulate logic gates. By wiring them up like this diodes can emulate both AND gates and OR gates. I hope this video was helpful. Now if you have any questions or doubts feel free to leave them down in the comment section below and if you want to watch more electronics crash course tutorials such as these do feel free to subscribe. Thanks for watching.