(Theory+Notes) Zener diode class 12 physics with handwritten notes


Semiconductors are of great use in our lives. From complex motherboard of your smartphones to simple circuits in your remote. All these things have some kind of semiconductor material in it.

One of the uses of these semiconductors is Zener diode. You may not have heard of it, but it's of great importance and in this article, we are going to explain to you about Zener diode and all the various things you need to know about it.

Before starting, let me give you the scientific definition of what a Zener diode basically is:

Zener diode is a reverse-biased heavily doped p-n junction diode that allows current to flow in a forward direction and it also allows to flow current in reverse direction but only if the voltage is above a certain level also known as the breakdown voltage. 

In this article, we have also provided you the handwritten notes PDF of semiconductor and Zener diode.

What are Semiconductors ?

Basics are always important and therefore instead of jumping straight into the Zener diode. We will first understand what semiconductor means ?

I can bet most of you already know about semiconductor but in case you don't, no need to worry we got your back.

So we all know that conductors can transfer electricity and insulator can't. Well property of semiconductors lies between conductor and insulator. 

In a certain condition where semiconductors will allow the transfer of electricity, there will be an available condition in which it stops the current or flow of electricity. 

This is the speciality of the semiconductor as this property can be used in many industries by using the appropriate type of semiconductor.

There are different types of semiconductors but generally, they are classified as p-type and n-type semiconductors.

In this article, I am not going to get deep into it but just wanted to give you a brief idea about the semiconductor.

If you want to learn more about semiconductors and p-type and n-type semiconductors. Read this article to get more info about it.

What is a Zener diode ?

As I told you earlier, Zener diode is a type of semiconductor which allows current when flows in forwarding direction and also allows current to flow when in reverse direction but there is a condition for reverse current. 
Zener diode and its symbol
If the voltage is above a certain level, only then Zener diode will allow flowing a current in reverse direction and this required voltage for reverse current to flow in Zener diode is known as the breakdown voltage.

Don't worry we will have a look into breakdown voltage as well in detail later in this article, but before going straight into the working of Zener diode, let's learn some basics first.

What is the Zener breakdown voltage ?

In order to explain to you, Zener breakdown voltage in simpler terms let me tell you the basic operation of a semiconductor.

So semiconductors have some unique properties as I told you earlier. One of these properties is allowing current in one direction and blocking it in the opposite direction. 

In the language of semiconductor, these two directions of current are known as forward biasing and reverse biasing.  

As the name suggests forward biasing means current is flowing in the forward direction and reverse biasing means its flowing in reverse direction.

Now when we are talking about Zener diode, it only allows forward biasing means current can only flow in the forward direction and not in reverse direction.  

So if you apply a reverse voltage in Zener diode circuits, current will not flow but here's where a breakdown voltage comes into play.

So if you want a reverse current to flow in the Zener diode circuits, you will need to apply high enough voltage above a certain level to make current flow in reverse direction. 

This certain level of voltage required for the flow of current in reverse direction in Zener diode circuits is known as breakdown voltage a.k.a Zener breakdown voltage.

Zener diode circuits:

In the previous section, we have been talking about when the reverse current will flow in a Zener diode circuits. 

So what are these Zener diode circuits actually and how many of them are out there? 

Well, there are so many types of Zener diode circuits out there made for a specific use.

Now in this article, we are only going to have a close look at a specific circuit only for one use: Zener diode as a voltage regulator. 

But don't forget that there are many other available circuits as well of Zender diode for different uses and applications. Here is the link to another article that has many other different circuits of Zener diode.

Zener diode as a voltage regulator:

A voltage regulator is a device that ensures that an output voltage remains the same and constant throughout a device.

It's an important device for all devices because in order to operate and work correctly all kinds of devices need a steady and constant voltage, irregular voltage or current can harm the circuit board and devices.

Zener diode helps us in making of a voltage regulator. Its property of breakdown voltage which we have discussed earlier plays a key role in voltage regulation.

Here is a link to step by step physics experiment of Zener diode as a voltage regulator and how its made.

I am giving you this YouTube video link to understand better how Zener diode is used in voltage regulation: 



V-I characteristic of Zener diode:

Now, the V-I graph is important to learn any property and characteristic of a semiconductor diode. It helps us to find how will the semiconductor perform if we increase the current or voltage in the circuit.

In case you don't know what V-I graph is, it's stand for Voltage - Current graph. Where 'V' represents voltage and 'I' represents current.

This graph shows what will be the voltage on a specific amount of current in a semiconductor or visa versa.

This V-I graph characteristic is different for different semiconductors. Let's have a look at how this graph will look in case of Zener diode:

V-I graph of Zener diode
Now, this is the graph of V-I for Zener diode and if you study this graph a little bit, in the right section you will notice that after a certain point, only current will increase and not voltage in forward bias.

Forward and reverse bias in V-I characteristic of Zener diode
Whereas if you look at the reverse bias part, you will note the same kind of trend but there is a negligible amount of current flows in reverse bias if you take a closer look, after a certain point (breakdown voltage) voltage can't be increased further and current starts flowing. 

This point of breakdown voltage is sharp and as soon as voltage hits this level, current starts to flow in reverse bias. 

This is also one of the main reasons why we use Zener diode in a voltage regulator.

What are the advantages and disadvantage of Zener diode ?

Now, there is a special reason why we are learning about Zener diode when there are so many different varieties of semiconductors and diodes present out there.

The simple answer to this question is, because of the property shown by Zener diode which is useful in many industries and tools and these properties are not shown by another semiconductor.

All these characteristics and property we have discussed just now, but there is much other reason as well for selecting Zener diode instead of another one which shows almost the same property.

With that it has some disadvantages as well so in this section of the article, I am going to give you the advantages and disadvantages of Zener diode.

S.no Advantages Disadvantages
1 Its less expensive Zener diode cancels out voltage by applying a high amount of voltage in reverse direction which is a waste of electricity
2 It can be used to regulate voltage It's not as good as a transistor in performance
3 Can control the flowing current
4 It's compatible with most of the circuits
5 Can easily work with smaller circuits that would not work with a high amount of current

Handwritten notes:

Now here are my personal handwritten notes for semiconductor and Zener diode. All the important things are cover in these notes, I hope you will like it ;) 

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