Diodes Explained - The basics how diodes work working principle pn junction

Summary

In this Engineering Mindset video, Paul explains the fundamentals of diodes, including their structure, the difference between anode and cathode, and their unidirectional current flow. He uses the water pipe analogy to illustrate how diodes act as conductors or insulators based on their orientation in a circuit. The video delves into the atomic structure of conductors, insulators, and semiconductors, detailing how doping creates the PN junction crucial for diode function. It covers diode applications, such as rectification and protection, and demonstrates how to test diodes using a multimeter, providing a comprehensive guide for understanding and utilizing diodes in electronic circuits.

Takeaways

• 🔌 A diode is a semiconductor device that allows current to flow in one direction only, with an anode and a cathode.
• 💡 Diodes are used to control the direction of current in a circuit, which is similar to a water valve allowing flow in one direction.
• 📚 The concept of electron flow and conventional current flow is explained, with electron flow being the actual movement of electrons from negative to positive.
• 🔍 The diode's function is demonstrated in a simple LED circuit, showing that the LED only lights up when the diode is correctly oriented.
• 🛠️ Diodes operate in forward bias when connected with the anode to positive and the cathode to negative, allowing current to flow.
• 🚫 In reverse bias, when the connections are reversed, the diode acts as an insulator, preventing current flow.
• 🧪 The internal structure of a diode is explored, including the PN junction formed by combining p-type and n-type doped silicon.
• ⚙️ The script explains semiconductor properties, contrasting them with conductors like copper and insulators like rubber.
• 🔋 Diodes have a specific voltage (around 0.7 volts) required to allow current flow, which is demonstrated through the IV (current-voltage) characteristics.
• 🔬 Diodes can be used for various applications, including protecting circuits from reverse current and converting AC to DC.
• 🛠️ The video script also covers how to test a diode using a multimeter, ensuring it only allows current flow in the forward bias.

Q & A

What is a diode and what does it look like?

A diode is an electronic component that allows current to flow in only one direction. It typically has a black cylindrical body with a stripe at one end and leads coming out for circuit connection. The stripe end is the anode, and the other end is the cathode.

What is the difference between the anode and cathode of a diode?

The anode is the end of the diode with a stripe, and it is connected to the positive side of the power supply when the diode is forward-biased. The cathode is the other end without the stripe, connected to the negative side of the power supply.

How does a diode control the direction of current in a circuit?

A diode controls the direction of current by allowing current to flow only when the anode is connected to the positive voltage and the cathode to the negative, a state known as forward bias. In reverse bias, where the connections are reversed, the diode acts as an insulator, preventing current flow.

What is the significance of the water pipe analogy used in the script?

The water pipe analogy is used to illustrate how a diode allows current to flow in one direction. Like water flowing through a pipe with a swing gate, current can only pass in one direction, and if the direction changes, the gate closes, preventing flow.

What are the two types of current flow conventions mentioned in the script?

The two types of current flow conventions mentioned are electron flow, where electrons flow from negative to positive, and conventional flow, where current is considered to flow from positive to negative.

Why do diodes have a voltage drop when they conduct?

Diode conduction involves overcoming a potential barrier within the diode, which is typically around 0.7 volts for a standard silicon diode. This potential difference creates a voltage drop when current flows through the diode.

What is the purpose of doping in semiconductor materials like silicon?

Doping is used to alter the electrical properties of semiconductors like silicon. By adding impurities, engineers can create p-type or n-type materials, which are then combined to form the diode's PN junction, enabling the diode to control current flow.

What is a PN junction and how does it form a diode?

A PN junction is a boundary between a p-type semiconductor, which has an excess of holes, and an n-type semiconductor, which has an excess of electrons. When these two materials are joined, they form a diode that allows current to flow in one direction due to the natural movement of electrons and holes.

How do diodes protect circuits from reverse current?

Diodes protect circuits by acting as insulators when reverse-biased, preventing current from flowing in the wrong direction and potentially damaging components.

What is the role of diodes in converting AC to DC?

Diodes are used in rectifiers to convert AC to DC by allowing only one half of the AC wave to pass through, thus creating a pulsating DC signal. This can be further refined using a full-wave rectifier and a smoothing capacitor to approximate a steady DC supply.

How can you test a diode with a multimeter?

To test a diode with a multimeter, connect the black probe to the diode's cathode (striped end) and the red probe to the anode (other end). The multimeter should show a reading if the diode is forward-biased. Reversing the probes should show an 'OL' (out of limits) reading, indicating the diode is blocking current flow.

Outlines

00:00

🔌 Introduction to Diodes

Paul from Engineering Mindset introduces the topic of diodes, explaining their physical appearance and basic function. Diodes are electronic components with a cylindrical body, a stripe, and leads for circuit connection. They have an anode and a cathode, which will be further explained. Diodes permit current flow in a single direction, analogous to a water pipe with a swing valve. The video uses electron flow for animation, contrasting with conventional current flow. A diode's operation is demonstrated in a simple LED circuit, showing that the LED lights up only when the diode is correctly oriented, highlighting the diode's role in controlling current direction.

05:02

🔬 How Diodes Work

The video delves into the atomic structure of conductors and insulators to explain how diodes function. Conductors like copper have free electrons that facilitate electricity flow, while insulators like rubber hold electrons tightly. Semiconductors like silicon have a conduction band close to the valence shell, allowing some electrons to become free with external energy. Diodes are made by combining p-type and n-type doped silicon, creating a PN junction with a depletion region that acts as a barrier to electron flow. The video explains forward bias, where the diode allows current flow, and reverse bias, where it acts as an insulator. Diodes are represented with symbols, and their IV (current-voltage) characteristics are discussed, including their voltage drop and the importance of selecting the correct diode for an application to prevent damage.

10:07

🔍 Testing Diodes

The final paragraph covers how to test diodes using a multimeter. It explains the procedure for checking the diode's forward voltage, which is the minimum voltage required to allow current flow, and the reverse configuration, where the diode should block current, indicating proper functionality. The video also demonstrates how to measure the voltage drop across a diode in a circuit, which is a key parameter for diode performance. The video concludes with a prompt to follow the channel on social media and to continue learning with more videos on the topic.

Keywords

💡Diode

A diode is a two-terminal electronic component that allows current to flow predominantly in one direction. In the video, it is described as having a black cylindrical body with a stripe at one end, which indicates the cathode, and leads for circuit connection. The diode is central to the video's theme as it is the primary device being explained. The script uses the diode to demonstrate the concept of unidirectional current flow, comparing it to a water pipe with a swing gate that allows water to flow in only one direction.

💡Anode

The anode is the positive terminal of a diode, which is the end without the stripe. It is one of the two main components of a diode, along with the cathode. In the video, the anode is mentioned as the point of connection when the diode is forward-biased, allowing current to flow into the diode. Understanding the role of the anode is crucial for comprehending how diodes control the direction of current in a circuit.

💡Cathode

The cathode is the negative terminal of a diode, indicated by the stripe on the diode's body. It is the end through which current exits when the diode is forward-biased. The video script explains that connecting the cathode to the negative terminal of a voltage source and the anode to the positive creates a forward bias, enabling current flow, which is essential for the functioning of diodes in electronic circuits.

💡Forward Bias

Forward bias is the condition where the anode of a diode is connected to the positive terminal and the cathode to the negative terminal of a voltage source, allowing current to flow through the diode. The video script uses the concept of forward bias to illustrate how a diode acts as a conductor when connected in the correct orientation, which is a fundamental principle in diode operation.

💡Reverse Bias

Reverse bias is the condition where the anode of a diode is connected to the negative terminal and the cathode to the positive terminal of a voltage source, preventing current flow. The video script explains that under reverse bias, the diode acts as an insulator, which is important for understanding how diodes can be used to protect circuits from unwanted current flow.

💡PN Junction

A PN junction is a boundary or interface between a P-type semiconductor and an N-type semiconductor. The video script describes how engineers combine these doped materials to form a diode. The PN junction is crucial for the diode's function as it creates a depletion region that acts as a barrier to current flow under reverse bias conditions.

💡Doping

Doping is the process of intentionally introducing impurities into a semiconductor material to change its electrical properties. The video script mentions P-type and N-type doping, where materials like phosphorus (for N-type) or boron (for P-type) are added to silicon to create the necessary conditions for a diode's operation. Doping is essential for creating the conductive and insulative properties within a diode.

💡Depletion Region

The depletion region is the area in a PN junction where the majority of charge carriers (electrons and holes) have been depleted due to their migration across the junction. The video script explains that this region forms a barrier that prevents further current flow under reverse bias, which is a key concept in understanding diode behavior.

💡IV Diagram

An IV (current-voltage) diagram is a graphical representation of the relationship between the current flowing through a device and the voltage across it. The video script refers to the IV diagram of a diode, which shows the diode's current-voltage characteristics and helps to understand the diode's performance as a conductor or insulator under different bias conditions.

💡Rectifier

A rectifier is a device that converts alternating current (AC) to direct current (DC). The video script describes how diodes can be used as rectifiers, allowing only one half of the AC wave to pass through, thus creating a rough DC signal. This concept is important for understanding how diodes are used in power supplies and other applications requiring DC power.

💡Voltage Drop

Voltage drop refers to the reduction in voltage across a component, such as a diode, due to its resistance to current flow. The video script mentions measuring a voltage drop across a diode when it is forward-biased, which is indicative of the diode's forward voltage and a normal characteristic of diode operation in a circuit.

Highlights

A diode is a semiconductor device that allows current to flow in only one direction.

The anode is the end with the stripe and the cathode is the black end of the diode.

Zener diodes and LEDs are special types of diodes but are not covered in this video.

Diodes are used to control the direction of current in a circuit, similar to a swing valve in a water pipe.

Electron flow is from negative to positive, while conventional current flow is from positive to negative.

A diode only allows current to flow when connected the correct way, acting as a conductor or insulator.

The forward bias allows current to flow when the anode is connected to positive and the cathode to negative.

The reverse bias acts as an insulator, preventing current flow when the diode is connected the opposite way.

Electricity is the flow of free electrons, with copper being a good conductor due to its many free electrons.

Semiconductors like silicon have a conduction band close to the valence shell, allowing some electron flow with external energy.

Doping silicon with other materials creates p-type and n-type semiconductors, which are used to form diodes.

The PN junction in a diode creates a depletion region that acts as a barrier to electron flow without sufficient voltage.

A forward bias overcomes the 0.7-volt barrier, allowing current to flow through the diode.

In reverse bias, the diode acts as an insulator, preventing current flow and expanding the depletion region.

Diodes have specific voltage and current ratings that must not be exceeded to prevent damage.

Diodes are used to protect circuits from反向电流 and to convert AC to DC through rectification.

Full wave rectification with four diodes and a capacitor can smooth out pulsating DC to mimic a steady DC supply.

Diodes can be tested with a multimeter to ensure they allow current flow in one direction and block it in the other.

Transcripts

Hey there guys, Paul here from Engineering mindset.com

In this video

We're going to be looking at diodes to understand the basics of how they work as well as where and why we use them so

What is a diode? A diode looks something like this and it comes in different sizes.

They typically have a black cylindrical body as a stripe at one end as well as some leads coming out to allow us to connect

It into a circuit this end is known as the anode and this end is the cathode

But we're going to see what that means later on in this video

You can also get other forms such as the Zener diode or an LED which is a light emitting diode

but we're not going to cover those in this video a

diode allows current to flow in only one direction in a circuit if

We imagine a water pipe or the swing valve installed as water flows through the pipe

It will push open the swing gate and continue to flow through

However, if the water changes direction the water will push the gate shut and it will prevent it from flowing

therefore water can only flow in one direction

This is very similar to a diode we use them to control the direction of current in a circuit

Now we've animated this video using electron flow which is where the electrons flow from the negative to the positive

However, you might be used to seeing conventional flow which is traditional in electronics engineering and this is where the electrons flow from the positive

to the negative

Electron flow is what's actually occurring

But you might come across

Conventional current still as these explanations are easier to understand just be aware of the two on which one we're using

So if we connect a diode into a simple led circuit like this one

we see that the LED will only turn on when the diode is installed the correct way and

That's because it allows current to flow in only one direction

So depending on which way the diode is installed. This will act as either a conductor or an insulator

In order for the diode to acts as a conductor

The stripe end is connected to the negative and the black end is connected to the positive

This allows current to flow we call this the forward bias

If we flip the diode, it will act as an initiator and the current can't flow and we call this the reverse bias

So, how does the diode work?

As you may know electricity is the flow of free electrons

but atoms we use copper wires because copper has a lot of free electrons, which makes it very easy to pass electricity through

We use rubber to insulate the copper wires and keep us safe

Because rubber is an insulator which means its electrons are held very tightly and they can't therefore move between our atoms

If we look at the basic model of an atom for a metal conductor

We have the nucleus at the center and this is surrounded by a number of orbital shells, which hold the electrons

Each shell holds a maximum number of electrons an electron has to have a certain amount of energy to be accepted into each shell

the electrons located far east away from the nucleus hold the most energy

The outermost shell is known as the valence shell and a conductor has between 1 and 3 electrons in its valence shell

The electrons are held in place by the nucleus, but there's another shell known as the conduction band

If an electron can reach this then it can break free from the atom and move to another

With a methyl atoms such as copper the conduction band and the valence shell overlap. So is very easy for the electron to move

With an insulator the outermost shell is packed. There's very little to no room for an electron to join

The nucleus has a tight grip on the electrons and the conduction band is far away

So electrons can't reach this to escape therefore electricity cannot flow through this material

However, there's another material known as a semiconductor

Silicon is example of a semiconductor with this material. There's one too many electrons in the outermost shell for it to be a conductor

So it acts as an insulator

But as the conduction band is quite close if we provide some external energy

Some electrons will gain enough energy to make the jump from the valence and into the conduction band to become free

Therefore this material can access both an insulator and a conductor if your silicon has almost no free electrons

So what engineers do is dope the silicon with a small amount of another material to change the electrical properties?

We call this p-type and n-type doping we combine these don't materials to form the diode

so inside the diode we have the two leads the anode and the cathode which connect to some thin plates and

Then between these plates there is a layer of p-type doped silicon on the anode side

And the layer of n-type types of cone on the cathode side

The whole thing is enclosed in a resin to insulate and protect the materials

Let's imagine the material hasn't been doped yet. So it's just pure silicon inside

Each silicon atom is surrounded by four of our silicon atoms

Each atom wants eight electrons in its valence shell

But the silicon atoms only have four electrons in their valence shell

So they sneakily share an electron with their neighboring atom to get their eight

They desire this is known as covalent bonding when we add in the n-type material such as phosphorus

It will take the position of some of the silicon atoms

The phosphorus atom has five electrons in its valence shell

So as the silicon atoms are sharing electrons to get their desired eight. They don't need this extra one

So there's now extra electrons in the material and these are therefore free to move

With p-type doping we add in a material such as aluminium or aluminium

This atom has only three electrons in its valence shell so it can't provide its four neighbors with an electron to share

So one of them will have to go without there is therefore a hole created where an electron can sit and occupy

So we now have two Doak pieces of silicon one with too many electrons and one we've not enough electrons

The two materials join to form a PN Junction at this Junction

We get was known as a depletion region in this region

Some of the excess electrons from the n-type side will move over to occupy the holes in the p-type side

This migration will form a barrier with a buildup of electrons and holes on opposite sides

The electrons are negatively charged and the holes are considered therefore positively charged

So the build-up causes a slightly negatively charged region and a slightly positively charged region

this creates an electric field and prevents more electrons from moving across the potential difference across this region is about

0.7 volts in typical diodes

When we connect a voltage source across the diode with the anode a p-type

Connected to the positive and the cathode n-type connected to the negative

This will create a forward bias and allow the current to flow

The voltage source has to be greater than the 0.7 volt barrier. Otherwise the electrons can't make the jump

When we reverse the power supply

So the positive is connected to the n-type cathode and the negative is connected to the p-type anode

The holes are pulled towards the negative and electrons are pulled towards the positive and this causes the bearer to expand

There for the diode acts as an insulator to prevent the flow of current

Diodes are represented in engineering drawings with symbols like these

The stripe on the body is indicated with a vertical line on the symbol and the arrow points in the direction of conventional current

When we look as a diode

We see these numbers and letters on the body these identify the diodes so you can find the technical details on line

The diode will have an IV diagram that looks something like this

This diagram plots the current and the voltage characteristics and forms this curve line

this side is how it should perform when acting as a conductor and this side when acting as an engine a tur

You can see that the diode can only act as an insulator

Up to a certain voltage difference across it. If you exceed this, then it will become a conductor and allow current to flow

This will destroy the diode and probably your circuit. So you need to make sure the diode is sized correctly for the application

Equally the dough can only handle a certain voltage or current in the forward bias

The value is different for each node

And you'll need to look up this data to find the details

The diode requires a certain voltage level to open and allow current to flow in the forward bias

If we apply a voltage less than this, it will not open and allow current to flow

But as we increase past that the amount of current that can float will rapidly increase

The diodes will also provide a voltage drop into the circuit

For example when they added this diode into the simple LED circuit mounted in a breadboard

I get a voltage drop reading of 0.7 1 volts

So why do we use them as?

Mentioned we used diodes to control the direction of current flow in the circuit

That's useful for example to protect our circuit if the power supply was connected back to front

The diode can block the current and keep our components safe

We can also use them to convert alternating current into direct current as you might know AC or alternating

current moves electrons forwards and backwards creating a sine wave with a positive and a negative half

But DC or direct current moves electrons in just one direction

Which gives us a flat line in the positive region if we connect the primary side of a transformer to an AC supplier?

And then connect the secondary side to a single diode

The diode would only allow half the wave to pass and it would block the current in the opposite

So the secondary side of the circuit experiences only the positive half of the cycle

So is therefore now a very rough DC circuit although the current pulsates, but we can improve this one way to do

That is if we connected for Dov's to the secondary site

we create a full wave rectifier the diodes controlled which paths for alternating current can flow long by blocking or allowing it to pass as

We just saw the diodes allow the positive half of the sine wave to pass

But this time the negative half is also allowed to pass

Although this has now been inverted to turn it into a positive half

Also, this gives us a better DC supply because the pulsating has greatly reduced, but we can still improve this further

We simply add in some capacitors to smooth out the ripple and eventually get it to a smooth line closely mimicking a DC supply

We've covered how capacitors work in great detail in our previous video do check that out links down below

So how do we test the diode? So we take our diode and our multimeter?

We connect the black probe to the end of the diode with the stripe

We then connect the red probe to the opposite end when we do this

We should get a reading on the screen. For example, this model one n400 one diode gives us a reading of

0.5 1 6 volts that is the minimum voltage it takes to open the diode to allow some current to flow if

We now reverse the leaves connected to the diode

We should see oh L on the screen, which means outside

limits that's telling us that it's not being able to make a measurement and that's a good thing because it means it can't complete the

Circuit so the doubt is doing its job

If we were to get a reading connecting on both configurations, then the component is faulty and shouldn't be used

to test the diode in a circuit for voltage drop

We simply move the multimeter into the DC voltage function and then we place the black probe on the striped end and the red probe

On the black end. This will give us a reading for example of

0.7 1 volts, which is the voltage drop

Okay, that's it for this video but to continual learning then check out one of the videos on screen now and I'll catch you there

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