Learning The Basics of a Diode [Easy and Quick Explanation]

Diode basics 2018

Hi. Hope you are having a good life. In this post, I am going to share with you everything I know about the basics of a diode. In my opinion, it is a very special component in learning basic electronics, as it is the part of almost every electronic circuit, and yet very simple to understand. I personally, found it very interesting. I remember my first power supply circuit designing, diodes were playing a major role in that circuit. Though at that time I did not have enough knowledge about but with time I learned a lot. And this post is all about what I have learned so far and will keep updating it as I learn new things about diode basics.

What is a Diode?

It is a device which has two terminals and capable of conducting electric current in only one direction. William Henry Eccles, an English physicist, came up with it in 1919 by combining the Greek roots di, meaning ‘two’, and ode, meaning ‘path’, though some sources say the ode was borrowed from ‘electrode’ which was coined by Michael Faraday.

A diode is an electronic component or a semiconductor device which allows current to flow in only one direction.

The capability of a diode to conduct electric current in only one direction makes it an ideal switch for low power loss. This capability also makes it the main building block a linear power supply. It is interesting to see how a diode allows the positive portion of a sine wave and blocks the negative portion.

Electrical Symbol of a Diode

In learning diode basics it is very important to know its electrical symbol. Just like other electronics components diode has got its own unique electrical symbol. Following is the electrical symbol of a diode. Have a look at it. You can clearly see its two terminals.

Diode Symbol

Diode Symbol

The two terminals are called anode and cathode. The anode is the positive terminal while the cathode is the negative terminal. A little current may flow in the other direction but it is so less that we neglect it. This current is called leakage current.

Forward and Reverse Biasing of a Diode

If you apply positive voltage to the anode and negative voltage to the cathode. You will see a current will start to flow through it. And this specific operation is called forward biasing the diode. The current that flows in a forward bias condition is called forward diode current.

Similarly, if you apply a negative voltage to the anode and positive to cathode you are reverse biasing a diode. And current following through the diode in reverse bias is leakage current. You know, this leakage current is too low but sometimes we do consider it and sometimes we neglect it.

Forward and Reverse Biased Diodes

In the forward bias region, the diode can be considered as a closed switch. While in reverse bias region it acts as an open switch. Keeping these points in mind, one can define a diode as a switch. In many circuits, it is used as a switch for it very low on state power loses, reliability and cost.

The VI Curve of a Diode

A VI graph of a diode shows a relation between the voltage across the diode and forward current through it. It is a very important curve to understand. Just like the transistor, a diode has it own VI curve. Following is the graph which is called the VI curve of the diode. Have a look at it and will explain everything about it

VI Curve of Diode

The curve is called VI curve because at X-axis you have voltage and at Y-axis you have current. The green region is the forward bias region. You can see that after the VF (Knee voltage), forward diode current increased. This means it is on and operating perfectly. Knee voltage differs for silicon and germanium diodes.

The pink region is reverse bias region. You can see a small leakage current is there in the reverse region but it is too low. In this state, the diode acts like an open switch providing an open circuit. Be careful when you are in the reverse region. Do not apply reverse voltage more than VBR (Voltage at break down region). If you do so, you will burn out your diode. It is a good practice to buy a diode with higher breakdown voltage.

Diodes in the Real Life

This is interesting, we got to know what is a diode. Now, we really need to have a look at its actual physical appearance. So that we can identify it on various electronics circuit board, or to just use it in our own electronics cool projects. Following is the picture of diode combined with its electrical symbol so you have a very clear idea of it.

Diode Symbol and Physical Diode

Remember the gray line. It will be a quick trick for you to identify the cathode terminal. I think it would be a cool activity if you can identify the diode yourself in the following picture. Can you tell, where is its cathode terminal? You can do this same activity with other pictures from these Google images.

Activity

The Current, Voltage and Power Ratings of a Diode

For proper operation of any device, you need to know its current, voltage and power ratings. These ratings tell us the minimum and maximum quantity of mentioned parameters to be applied to a certain device. Current ratings of a diode tell us the minimum and maximum current it can support. And the same definition goes for the rest of the parameters.

The datasheet is the only source to find these ratings for any diode. Datasheets are made by manufacturers so that everyone can use it to make their projects perfectly without damaging any device. Reading a datasheet is very important and sometimes people do not understand how to look for specific information in it. I am going to help you with this problem

I will take the example of  1N4001, and I will show you how to read these parameters from its datasheet.

  • First, you download the datasheet for your diode.
  • Go to the section: “Maximum Ratings and Electrical Characteristics”. It is not necessary to be exactly like it. But I think you got the idea.

Reading the Datasheet of a Diode

Following is the datasheet for 1N4001. Can you see the voltage and current ratings in it?

1n4001 Datasheet

In the first-row peak reverse voltage is given. This is the voltage across the diode when it is OFF (reverse biased). Do not apply voltage more than this, you can burn it out. The second row is giving the same information but in RMS terminology. RMS Reverse Voltage is same as DC blocking voltage. Fifth-row providing information about the maximum forward current a diode can safely handle. To limit this forward current, a series resistor is placed before the diode.

You may wonder about the power rating, right? We can simply multiply current and voltage to get the required power rating. For the present 1N4001 power rating is 50W (50V x 1A ). You can see a peak reverse current in the sixth row. Here you can see yourself it is too low as I told you earlier. Always refer to the datasheet of your device. Do not apply voltage without proper information, chances are you may damage your device.

Testing a Diode

Testing a diode means to check whether it’s working properly or not. An easy way to do it by using a multimeter. Following video explains step by step approach to test a diode using a multimeter.

Types of diode

There are a lot of different types of diodes out there in the market. Operation of diodes are almost the same but their properties get changed. Some diodes are faster. Some are having more power handling capability. Following is the list of all different diodes.

  1. Zener diode: Allows current to flow not only from its anode to its cathode but also in the reverse direction. It is used in voltage regulations.
  2. P-N junction diode
  3. Tunnel diode: It has a very fast operation, well into the microwave frequency region.
  4. Varactor diode: It acts like a variable capacitor under reverse bias.
  5. Schottky diode: It is a metal-semiconductor junction diode that consumes less power than the P-N junction diode.
  6. Photo diode: It converts light into an electrical current
  7. PIN diode: It is suitable for attenuators, fast switches, photo detectors, and high voltage power electronics applications.
  8. Laser diode: It produces coherent radiation.

Applications of Diodes

Despite being just simple two-pin semiconductor devices, diodes are vital in modern electronics. Almost every electronic circuit has a diode inside of it.  Some of the typical applications of diodes include:

  • Conversion of AC to DC (Rectifier circuits)
  • Voltage multipliers
  • Protection of many other devices
  • Clipping and clamping a signal (clipper and clamper circuits)
  • Mixing signals (Mixer circuits)

1. The Rectifier Circuits

Every circuit needs power for its proper operation. And trust me almost every circuit works on DC power. But we all know AC power is coming to our homes, not DC power. We need a third man to convert the coming AC to DC.  This third man is a rectifier circuit. Rectifier circuit converts AC to DC so that we power up DC devices like our mobile phones. This rectifier circuit is made possible due to the invention of diodes. It is a great application of diodes. Without a rectifier circuit, we could not be able to convert AC to DC.

2. The Voltage Multipliers

Sometimes we need different voltage levels in the same circuit. Instead of designing separate power supplies, voltage multipliers circuits are used. As the name indicated, voltage multipliers are a combination of diodes and capacitors which produce high voltage levels from a reference voltage level. In other words, voltage multipliers are used to produce high DC voltage levels form small AC voltage levels.

3. Protection

Providing protection is one of the major applications of the diode. Consider, for example, your car. When your battery dies and a friendly passerby offers to help with jumper cables, if you mix the order of the red and black cables you won’t fry your car’s electrical system because of diodes adjacent to the battery block the wrong-direction current.

Using power transistor, or DC motor in your application: pre-wheeling diode plays a key role in protecting other circuit components from reverse current.

4. The Clipper and Clamper Circuits

Clipper is a limiting circuit which limits the output voltage while clamper is a circuit which shifts the DC level of output voltage. Clipping of signal amplitude is required in some application in which components cannot withstand the high magnitude of the voltage. While clamper is used when we need multiples of the input voltage at the output terminal.

5. The Mixer Circuit

One of the simpler mixer circuits is based around two diodes. This type of diode known as a single balanced diode mixer circuit provides rejection of the input signals at the output as a result of the fact that the two inputs are balanced.

Summary of Diode Basics

  • The diode is a semiconductor device which allows current flow in one direction
  • There are two operating conditions of a diode 1) Forward bias condition 2) Reverse bias condition
  • When using a diode make sure you download its datasheet and check for its current, voltage and power ratings.
  • Gray bar on physical diode represents the cathode terminal.
  • You can actually test a diode by using any digital multimeter.

References

This was all I know myself about diode basics. Hopefully, it has helped you somehow. If you have any suggestion or question please contact me or leave a comment. I really appreciate it from the heart.

You can also check my other fun posts:

Thank you and have a good life.

2 Comments

  1. Irfanullah Reply

    A.o.A sir it is very helpful for students ..Thank u for sharing ur precious ideas and helping students to understand Electronics… We are anxiously awaiting for more posts …

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