June 22, 2024

What is transistor? Definition, symbol, construction & terminals of transistor

what is transistor
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if you find the transistor basics than you are at right place. Here we know what is transistor? and types of transistor. Transistor definition, PNP and NPN transistor symbol, construction of transistor, the different configuration of a transistor and much more. So let see in details.


What is transistor?

The transistor is one type of switching device which consists of 3 semiconductors and 2 junctions. The transistor is an electronic device which is capable of achieving amplification of the weak signal.

In the Past, vacuum tubes are used instead over transistor but now transistor has so many advantages over there. Transistor have no filament and hence there is no heating power and this may be operated in any positions. The transistor is mechanically so strong and has a great life spam so transistor does a better job than vacuums tubs. Transistor was invented by J.Bardeen and W.H Brattin which is a great movement in electronics application. So, now transistor has become the heart of the most electronics devices. Let we discuss the proper definition of the transistor.

what is transistor

Transistor definition

A device which consists of p and n-type semiconductors and formed 2 PN junctions is called a transistor. Transistor has mainly two types

  1. PNP transistor
  2. NPN transistor

pnp and npn transistor

Definition of NPN transistor –  A transistor which composed of two n-type semiconductors and separated by p-type semiconductors is called NPN transistor. This types of transistor device fig is shown below.

Definition of PNP transistor – A transistor which composed of two p-type semiconductors and separated by n-type semiconductors is called PNP transistor. This types of transistor devices fig shown below.

For the transistor, you have to first clear this fact

  • Transistor has two PN junctions. So that transistor is also called as the combination of two diodes which is connected back to back.
  • Transistor contain three terminals and each terminal are taken from the semiconductors
  • The middle section is a thin layer which is the most important part in the structure of the transistor device.

Transistor symbols

In earlier, we see the types of transistors and now we see the symbols of this 2 transistors. Below you can see the symbol of the PNP and NPN transistors. Transistors have a special symbol related to their structure see below –

PNP transistor symbol:-

pnp transistor symbol

NPN transistor symbol

npn transistor symbol

Construction of transistor

Transistor has mainly three terminals. Probably you see this three terminal in the figure. Transistor has an emitter, base, and collector this three terminals. The middle section of the transistor is called base. let discuss all their terminals in details

  1. Emitter: The section on one side of a transistor which carries electrons or holes is emitter terminal. If there is PNP type transistor then emitter is p-type semiconductors so it contains holes. If there is NPN type transistor then emitter contains electrons. an emitter is always connected in forwarding bias with a base so that it supplies a large number of holes or electrons towards the base. In PNP transistor emitter-base junction is in forward bias and emitter supplies large numbers of holes in the base. As the same in npn large numbers of electrons transfer towards the base.
  2. Base: Base is the middle section of a transistor and it receives majority carrier holes or electrons from an emitter. Base-emitter is in forward bias so it has a very low resistive path. but base-collector junctions is in reverse bias so it has a high resistive path. you can see in the figure.transistor construction, terminals
  3. Collector: The section on one end other side is called the collector. Collector-base junction is always in reverse bias so that it has very high resistance. in PNP type transistor collector is p-type so it receives holes charges and an NPN type transistor collector is n-type so it receives electrons charges.

Some facts about transistor regions

The following facts about the transistor region read carefully to understand the basis of the transistor –

  1. Transistor has mainly three regions: emitter, base, and collector. Furthermore here base region is much thinner than the other two regions.
  2.  The emitter region is heavily doped so that there is large numbers of charge carrier contain b emitter region. A base region is a thin layer and receives a charge carrier from the emitter region. The collector is moderately doped.
  3. Transistor has two junctions like two diodes. The junction between emitter and base is called an emitter diode and another junction between base and collector is called collector diode also.
  4. Emitter and base junction or emitter diode is always in forwarding bias and very low resistance. or in contrast, base-collector junction or collector diode is always in reverse bias and very high resistance with respect to emitter diode.

Transistor different configuration

The transistor can be connected in a circuit with different configurations. Transistor has mainly three types of configuration in circuits. Different transistor configuration used in circuits as per their requirements. Transistor has the following configuration:

>> Common emitter type configuration

>> Common base type configuration

>> Common collector type configuration

Some brief applications of transistor configuration: common emitter type transistor is mainly used in practical life. The common emitter is used in many amplifying circuits for amplifying weak signals. Common base and common collector type configuration also used but it used rarely. Common base connection circuits provide good current gain, common collector type connection provides good voltage gain. Common emitter ( CE ) type circuits provide high current gain and high voltage gain. So, that CE transistor is the first choice in amplifying applications circuits.


Transistor is an essential part of the electronics circuit. Most of every electronics used today are used in same manner of the transistor circuit. Transistor is the heart of any electronic control circuit ans switching circuit. For fast switching it is mainly used.

Hope you understand all topics related to the transistor – what is a transistor and types of transistor, transistor symbols, construction and terminals of transistors. if you have any doubt then feel free to comment below.

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