PN Junction Diode Working in Forward Biasing and Reverse Biasing by Shubham Kola

Shubham Kola

Subject - Basics of Electronics  Chapter - PN Junction Diode

Transcript

00:00In this video, we are going to learn, construction and working of p-n junction diode and its

00:13application in real life.

00:17The p-n junction diode are an important part of many devices you use everyday.

00:24Like your phone charger or the circuits inside your home appliances.

00:31By the end of this lesson, you will understand how the p-n junction diode works and how it

00:36is used in real life.

00:38First, let's understand what a p-n junction diode is.

00:44To do this, we need to know two key terms, that is p-type material and n-type material.

00:54p-type material Imagine a material where there are some missing

00:58electrons creating holes where electrons could be.

01:04These holes behave like positive charges because they attract electrons.

01:11This type of material is called p-type material because it has a positive nature.

01:18n-type material Now, think of a material that has few extra

01:22electrons.

01:23These extra electrons can move around and carry a negative charge.

01:29This material is called n-type material because it has a negative nature.

01:36When we place p-type material and n-type material next to each other, they form a p-n junction.

01:45This junction creates a diode.

01:49The diode is a device that allows electric current to flow in only one direction while

01:55blocking it in the other direction.

01:58So first, we will see the formation of p-n junction.

02:03When p-type and n-type materials come together, something interesting happens at the boundary

02:08called the junction.

02:11At first, electrons from the n-type material move into the p-type material to fill the

02:16holes.

02:17Similarly, holes from p-type material move into n-type material.

02:25As electrons move into p-type material, they fill some holes.

02:30And as holes move into n-type material, they leave behind negatively charged ions.

02:37This movement of electrons and holes doesn't continue forever.

02:41Soon, a region forms near the junction where there is no free electrons or holes.

02:49This area is called the depletion region because it has no mobile charge carriers.

02:56The depletion region acts like a barrier that prevents further movement of electrons and

03:02holes across the junction.

03:05It is like a shield that stops charges from freely moving across.

03:10Now, we will see the working of p-n junction diode.

03:17Now that we know what a p-n junction is, let's talk about how the diode works when we apply

03:24an external voltage.

03:28When we connect the positive terminal of a battery to the p-type material and the negative

03:33terminal of a battery to the n-type material, we are forward biasing the diode.

03:41In this condition, the external voltage pushes electrons in n-type material towards the junction

03:49and it pushes the holes in p-type material towards the junction as well.

03:56If the applied voltage is strong enough to overcome the barrier created by the depletion

04:01region, the electrons and holes can cross the junction and current flows through the

04:06diode.

04:08The diode is ON in this state, allowing electricity to pass.

04:15If you reverse the battery connection, positive to n-type and negative to p-type, you are

04:21reverse biasing the diode.

04:24In this case, the external voltage pulls the electrons in n-type material away from the

04:30junction and does the same to the holes in the p-type material.

04:36This action widens the depletion region, making it even harder for any charge carriers to

04:42cross the junction.

04:45As a result, the diode blocks the flow of current, acting like an OFF switch.

04:53Now we will see real-life applications of p-n junction diode.

04:59The p-n junction diode is not just a theoretical concept.

05:03It is used in many practical applications.

05:06Let's look at some of these.

05:09First is rectifiers.

05:12One of the most common uses of a diode is in converting AC current to DC current.

05:19This process is known as rectification.

05:23In devices like phone chargers, the AC from wall socket is converted into DC using diodes.

05:32Next is voltage regulation.

05:34Diodes are also used in voltage regulation circuits to maintain a constant output voltage.

05:42Zener diodes, a special type of diode, are designed to allow current to flow in the reverse

05:46direction when a certain voltage is reached.

05:50This property is used to keep the voltage across the load constant, protecting CC2 electrons

05:57from voltage spikes.

06:00Next is signal demodulation.

06:04In radio receivers, diodes are used to demodulate signals, which means they help in extracting

06:11the original information from a modulated carrier wave.

06:15Next is protection circuits.

06:18Diodes are often used to protect circuits from voltage spikes.

06:23For example, flyback diodes are used in circuits with inductive loads like motors to prevent

06:30damage when the current is suddenly interrupted.

06:34A light-emitting diode, LED, is a special type of diode that emits light when current

06:41flows through it in the forward direction.

06:46For more information, visit www.fema.gov

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