Transistors
In common terms we took the transistors as a switching device but in real it is also an amplifier device which is used to amplify the week signals and convert them into powerful signal. Multistage transistors are used to amplify a week signal into high power signal for transmission from one transmitter to the other receiver circuit.
Introduction
The development of electronics industry as we see today started with the invention of a transistor. The working of the transistor can be understood easily if you already have the knowledge about semiconductor diodes. If you don’t have any knowledge about diodes, don’t worry. This tutorial will provide a complete guide about transistors which helps beginners to easily understand the concept.
In the previous tutorials, we saw that diodes are made up of the combination of n-type and p-type semiconductor. When a p-type semiconductor is joined with the n-type semiconductor, a p-n junction is formed between them. This p-n junction forms a most popular device known as a semiconductor diode. An addition of another layer to a p-n junction diode forms a three terminal device called a transistor. The term transistor normally refers to a Bipolar Junction Transistor (BJT).
Like a p-n junction diode, a transistor is also made up of the combination of the p-type and n-type semiconductor layers. However, unlike the p-n junction diode, the transistor contains either one p-type and two n-type semiconductor layers or one n-type and two p-type semiconductor layers.
The transistor that is made up of one p-type and two n-type semiconductor layers is known as n-p-n transistor whereas the transistor that is made up of one n-type and two p-type semiconductor layers is known as p-n-p transistor.
N-type and p-type semiconductors are the extrinsic semiconductors. In the n-type semiconductor, free electrons are the majority charge carriers and holes are the minority charge carriers whereas in the p-type semiconductor, holes are the majority charge carriers and free electrons are the minority charge carriers. Therefore, in n-type semiconductor free electrons carry most of the current whereas in p-type semiconductor holes carry most of the current.
Transistor definition
A transistor is a three-terminal semiconductor device that amplifies or switches the flow of current.
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A transistor is an electronic device that controls the current flow or switches the current flow.
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A transistor is an electronic device that controls the movement of electrons (charge carriers).
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A transistor is a small electronic device that controls the flow of electric current.
Brief history of transistors
The transistor was successfully demonstrated on December 23, 1947 at Bell Laboratories, New Jersey. The three individuals credited with the invention of the transistor were John Bardeen, William Shockley, and Walter Brattain. Among these three individuals, William Shockley played a key role in the invention of the transistor.
What is transistor?
A transistor is a three-terminal semiconductor device that amplifies the electronic signals such as radio and television signals. Before the transistors came into existence, vacuum tubes are used to amplify the electronic signals. But nowadays vacuum tubes are replaced by transistors because of its various advantages over vacuum tubes.
The various advantages and disadvantages of transistors and vacuum tubes are as follows:
Advantages of vacuum tubes
- Vacuum tubes can be easily replaced.
- Tolerant of large overloads and voltage spikes
- Superior sound quality
Disadvantages of vacuum tubes
- High power consumption
- High cost
- Vacuum tubes are very bulky. So they occupy more space.
- High voltage is needed to operate the vacuum tubes.
- Produce large heat
- Lower efficiency
Advantages of transistors
- Low power consumption
- Low cost
- Small size
- Higher efficiency
- Low voltage is needed to operate the transistors
- High physical ruggedness than vacuum tubes
- Produce far less heat than vacuum tubes
- Transistors are lighter than vacuum tubes
Disadvantages of transistors
- Less tolerant of overloads and voltage spikes than vacuum tubes
- Maintenance is very difficult
- It is difficult to replace the transistor
Classification of transistors
The transistors classification can be understood by observing the below tree diagram.
The transistors are mainly classified into two types: Bipolar Junction Transistor (BJT) and Field Effect Transistor (FET). In Bipolar Junction Transistor (BJT), both free electrons and holes conduct electric current whereas in Field Effect Transistor (FET) either free electrons or holes conduct electric current.
The Bipolar Junction Transistors (BJTs) are again classified into two types: they are NPN and PNP transistors.
The Field Effect Transistors (FETs) are classified into two types: JFET and MOSFET. JFET stands for Junction Field Effect Transistor and MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor.
The Junction Field Effect Transistors (JFETs) in depletion mode are classified into two types: N-channel and P-channel.
The MOSFET transistors are classified into two types: depletion mode MOSFET and enhancement mode MOSFET.
The depletion mode MOSFET is classified into two types: N-channel and P-channel.
The enhancement mode MOSFET is classified into two types: N-channel and P-channel.
