What is a transistor?
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| Transistors |
Transistor is a three terminal semiconductor device. The two main function of the transistor is to amplify or switch electronic signal or electric current.
“Trans” means transfer property and “istor” means resistance property. It means it switches with some resistance or control.
It is the fundamental building block of the modern electronics. Transistor was invented by John Bardeen, Walter Brattain, and William Shockley in the Bell Laboratory in the year 1947.
Advantage of Transistor over vacuum tube:
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| Vacuum tubes |
Before transistor was invented Vacuum tubes were used. It was successful but the disadvantage is it was bulky, expensive, efficiency was low.
Since the cathode got heated up, the life time of the vacuum tube was short. To overcome all these disadvantages transistor was invented.
Function of the transistors:
Works as an Amplifier:
Transistor takes in a small electric current and amplifiers into a bigger current. For example in hearing aids the tiny microphones collect the sound around and convert it into electric current and it is given as the input to the transistor.
The transistor boosts and amplifies that electric signal and give it as the output to the loudspeaker. Thus we can hear the louder version of the sound.
Works as a Switch:
Transistor controls the flow of current or voltage and acts as a switch or gate for the electronic signals, like the faucet valve which controls flows of the water. For example the memory chip consists of millions and billions of transistors and each individual transistor can be switched ON or OFF.
Types of transistors:
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| Types of transistors |
Three terminals of the Bipolar Junction transistors:
The three terminals in the BJT are named as emitter, base and collector.
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| Three terminals of BJT |
Emitter:
Emitter terminal is heavily doped when compared to other two regions. It is larger than the base in size and slightly smaller than the collector. It is moderate in size. Emitter is heavily doped because it provides charge carriers to the collector through the base.
Base:
Base is the middle region. It is very lightly doped so that the majority charge carriers from the emitter doesn’t combine in the base region and it passes to the collector. Size of the base region is also very smaller than the emitter and collector. Base emitter forms the input circuit and base collector forms the output circuit.
Collector:
Collector region is larger in size than the base and the emitter. Inorder to dissipate the heat due to the recombination and collection of the charge carriers the size is larger than the other two regions.
Three terminals of the Field Effect transistors:
Similar to the terminals in the BJT, in FET also there are three terminals they are gate source and drain. Additionally FET has a body or a channel.
Three terminals of FET
Source:
The majority carriers enter the Field Effect transistor through the source terminal.
Gate:
By controlling the Gate voltage the flow of majority carriers from Source to drain can be controlled.
Drain:
The majority charge carriers leaves the channel through drain. This current is designated by the source gate voltage VGS
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