How transistor work? - Explain in details

How transistor work? - Explain in details

Transistor is one of the most popular electronic components that can do two different works. It can function as an amplifier or a switch. There are so many types of transistors used in electronics according to their characteristics and applications.

Transistors like BJT(Bipolar Junction Transistor), FET(Field Effect Transistor) are used in electronics. Junction Transistor can be of two types PNP transistor and NPN transistor and there are two types of Field Effect Transistor - Junction Field Effect Transistor(JFET) and Metal-Oxide Field Effect Transistor(MOSFET). In this tutorial, we are going to learn about how Bipolar Junction Transistor(BJT) work.


How transistor work?



With transistor, a larger supply of electricity can be controlled by using a small amount of electricity, It's much like to control a supply of water by turning a valve


Transistor has it's three parts -


1. Base

2. Emitter
3. Collector


How transistor work? - Explain in details


In the transistor, the base is used as a gate to control the larger electrical supply. The collector is used as a larger electrical supply and emitter is works as the outlet for this supply.

By applying different levels of electric current from the base, the amount of flowing current through the gate from the collector can be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier.


How NPN transistor work?



Basically, Transistors are made of semiconductor materials. Depending on this materials there are two types of Biopolar Junction Transistor - NPN transistor and PNP transistor

NPN transistor has three legs - Base, Emitter, and the Collector. In the NPN transistor, the collector and emitter regions are made up of N-type material, which is mainly composed of electrons. The base region is made up of P-type material, which is mainly composed of holes.

In the NPN transistor current flows from collector to the emitter. for this type of flowing the biasing must be followed in this way
How transistor work? - Explain in details

If you understand the law of charges then you can easily figure out how a transistor works. it is a very simple concept. It is the concept where the same charges repel each other and opposite charges attract each other.

This means two positive charges will repel each other and two negative charges will repel each other, while the opposite charges will attract each other. This is all you need to know to understand transistors.

As we know before, In NPN transistor the emitter regions that made up of N-type material, where majority carriers are electrons that are negative charges.

Now we want to flow current from the collector to the emitter region. So, we place a positive voltage to the emitter region. As a result, the electrons in the collector terminal are repelled by this voltage and current will flow toward the emitter.



Now we apply a voltage in the base region which is made up of P-type material. It is the most important region for controlling the on/off capability of the transistor.

If there is no current is going into the base region of the transistor then it offers strong resistance to the flow of current. So the current does not flow from collector to emitter.

This is why the P material comprising the base region, made up of holes, provides a strong barrier that separates the collector and emitter regions.

However, when current flows into the base, the electrons start to flow into the P material and depleting the number of holes in the base region.

The base region barrier becomes depleted, becoming smaller until there are enough electrons filling it to completely break down the barrier. When this occurs, the current can easily flow from collector to emitter.

Now to connect an NPN transistor we need the following circuit



How transistor work? - Explain in details

After connecting the circuit if you apply a sufficient current into the base then the transistor becomes on. And if you remove this current from the base then it becomes off.


How PNP transistor work?



PNP transistor also has three legs - Base, Emitter, and the Collector. The collector and emitter regions are made up of P-type material, which is mainly composed of holes. The base region is made up of N-type material, which is mainly composed of electrons.

In the PNP transistor current flows from emitter to the collector. for this type of flowing the biasing must be followed in this way
How transistor work? - Explain in details

As we know before, In PNP transistor the emitter regions that made up of P-type material, where majority carriers are holes that are positive charges. Now we want to flow current from the emitter to the collector region. So, we place a positive voltage to the emitter region. As a result, the holes in the emitter terminal are repelled by this voltage and current will flow toward the collector.



Now we apply a voltage in the base region which is made up of N-type material. It is the most important region for controlling the on/off capability of the transistor. If there is no current is going into the base region of the transistor then it offers no resistance to the flow of current. So the current can easily flow from emitter to collector.

This is why the N material comprising the base region, made up of electrons. Now If we give more electrons, by applying current then the thickness of the base region is increased and it blocked the flow of current from the emitter to the collector.

This is why when we give current to the base of a PNP transistor then it blocks the flow of current from the emitter to the collector. And when there is no current flowing from the base then current can easily flow from emitter to collector.

Now to connect a PNP transistor we need the following circuit

How transistor work? - Explain in details

After connecting the circuit if you apply a sufficient current into the base then the transistor becomes off. And if you remove this current from the base then it becomes on.
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