Scientific Aspect
Click to learn about the development of this transistor
This is one of the earliest transistors that is considered to be fundamentally important.
The Bipolar Junction Transistor (BJT) consists of three different regions, sandwiched together. The outer two layers are of the same type, while the middle layer is different Hence we have two different types of BJTs -
n-p-n transistors with a p-region sandwiched between two n-regions
In either type, the region that occurs only once (p-region in n-p-n or n-region in p-n-p) is very small with very few charge carriers (i.e. holes or electrons) and is called Base.The other two regions are bigger in size.
Working:
We shall consider the working of an n-p-n transistor. In the use of this transistor, the current is made to enter through one n-region.
Let us now review the passage of current through the passage of current within the transistor:
Thus the transfer of current from a low resistor circuit to a high resistor circuit is successfully obtained. Here, the former n-region may be said to emit the electrons into the latter n-region which collects these electrons. So the region where the current enters the transistor is called as Emitter and the other region is called as Collector.
The same working is true for p-n-p transistors, but the electrons are replaced by holes.
Construction:
and
p-n-p transistors with n-region sandwiched between the two p-regions.
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C
onstruction:
The BJT has three different layers sandwiched together. If an n-type semiconductor is added to the p-side of a p-n junction diode, then it results in the formation of an n-p-n type of transistor. Adding a p-type semiconductor to the n-side forms a p-n-p type transistor. Hence its two types are n-p-n and p-n-p |
 Circuit symbol of BJT |
However, the middle layer called the Base is very thin and lightly doped. Of the outer regions, one is called the Emitter and is very heavily doped and the other is called the Collector and is less heavily doped in comparison to the Emitter.
Working:
Play Stop
Consider the working of an n-p-n type of BJT. It is generally connected such that the Emitter and the Base are forward-biased and the Base and Collector are reverse-biased. This biasing is ensured by the application of a voltage that is different from the input voltage. However, this voltage is steady, direct voltage and the input voltage may be alternating voltage. When the current passes through the circuit, the Emitter-Base junction being forward-biased, most of the electrons from the Emitter flow towards the Base.
However, the Base, as mentioned above, is very lightly doped. As a result, very few of the electrons entering from the Emitter constitute the Base current. The remaining electrons (almost 95%) flow into the Collector region.
These excess electrons ensure that the current flows through the reverse-biased Base-Collector junction. As this reverse-biased circuit has a very high resistance, the voltage obtained too is equally high. Moreover, this voltage depends upon the electrons entering the Collector from the Emitter, which in turn depends upon the input voltage and so the output voltage has a higher magnitude (amplitude), but the same frequency as the input voltage.
The same explanation holds true for the p-n-p transistors. Only, electrons are replaced by holes and voltage direction shown in the diagram will have to be reversed.
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Introduction to Semiconductors
This topic will introduce you to the concept of semiconductors which are an integral part in the making of transistors. |
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Semiconductor Diodes
The prerequisite information on diodes that later went on to give the birth to the semiconductor triode - otherwise known as the transistor. |
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Semiconductor Triodes
Another name for the transistor... |
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Types of Transistors
Learn the various types of transistors and how they function. |
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Amplification
This is the basic function of the transistor - and the most important one! |
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Switches
Next to amplification, this is the most common function of transistors. |
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Comparisions
Learn the analogies and the differences between the older vacuum tube triodes and the slicker new transistors. |
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Integrated circuits
These are the most common applications of transistors and go a long way in building powerful microprocessors and appliances. Learn the role that transistors play in them. |
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Microprocessors
These are the real brains of most electronic appliances around us. Explore the vital role played by their grey cells - transistors. |
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Appliances affected
Realize the full potential of these transistors through the various appliances they revolutionized, right from your digital watch to this PC. |
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The pre- and post-transistor world
To understand the impact of the transistor in its entirety, perceive what the world was before, and what it is after 1947 - when the transistor was invented. |
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Future trends
Revolution is an unending process. Take a sneak preview of where the transistors of the future are headed. |
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History
Understanding of the transistor becomes clearer when learnt in context of its evolutionary journey. Here, we have presented the most important landmarks in its journey of almost a century. |
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Build the transistor
Theoretical knowledge weighs nothing unless put to practice. Learn how the different types of transistors are built and build some on your own! |
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Learn the circuits
Learn how the actual amplification and switching takes place by building your own circuits and watching the current flow. |
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Drive-the-circuit
If you have the necessary stuff in your head, come and test drive a BJT amplification circuit! But watch out for the speed bumps along the way! |
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Basic Section
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Development of PCT
Learn the development of Point Contact Transistor. |
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Development of BJT
Learn the development of Bipolar Junction Transistor Transistor. |
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Development of JFET
Learn the development of Junction Field Effect Transistor. |
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Development of MOSFET
Learn the development of Metal Oxide Semiconductor Field Effect Transistor. |
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Scientific Aspects of PCT
Learn the scientific aspects of Point Contact Transistor. |
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Scientific Aspects of BJT
Learn the scientific aspects of Bipolar Junction Transistor. |
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Scientific Aspects of JFET
Learn the scientific aspects of Junction Field Effect Transistor. |
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Scientific Aspects of MOSFET
Learn the scientific aspects of Metal Oxide Semiconductor Field Effect Transistor. |
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Prerequisites
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