Bipolar Junction Transistors Working Principle and Applications

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This article discuss about the Bipolar Transistor also called Bipolar Junction Transistors or BJT including the Types, working and applications

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Bipolar Junction Transistors Working Principle and Applications

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http://www.elprocus.com/ Introduction: Bipolar Junction Transistors Working Principle and Applications BJT was invented in 1948 by William Shockley, Brattain, and John Bardeen which has remolded not only the world of electronics but also in our day to day life. The basic of electronic system nowadays is semiconductor device. The famous and commonly use of this device is BJTs (Bipolar Junction Transistors). It can be use as amplifier and logic switches. Lets look into BJT types, working principles.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications What is a Bipolar Junction Transistors (BJT)? The Bipolar junction transistor is a solid state device and in the BJTs the current flow in two terminals, they are emitter and collector and the amount of current controlled by the third terminal i.e. base terminal. It is different to the other type of transistor i.e. Field effect transistor which is the output current is controlled by the input voltage. 

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Symbol of The BJTs Common Emitter (CE ). Common Base (CB ). Common Collector (CC).

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Types of Bipolar Junction Transistors The bipolar junction transistors consist of two types of transistors. Which, given us Point contact Junction transistor Further the junction transistors are classified into two types which are PNP junction transistors NPN junction transistors There are three electrodes for each junction transistor they are emitter, collector, and base.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications PNP Junction Transistor In PNP transistor, the emitter is more positive with base and also with respect to the collector.  The PNP transistor is a three terminal device which is made from the semiconductor material . The three terminals are collector, base, and the emitter and the transistor. It is used for switching and amplifying applications.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Operation of PNP Transistor the collector terminal is connected to the positive terminal. the emitter to a negative supply with resistor either the emitter or collector circuit.  To the base terminal the voltage is applied and it operates transistor as an ON/OFF state.  The transistor is in OFF state when the base voltage is same as the emitter voltage .

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Operation of PNP Transistor The transistor mode is in ON state when the base voltage decreases with respect to the emitter . By using this property the transistor can act on both applications like switch and amplifier . The basic diagram of PNP transistor is shown below.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications NPN Junction Transistor The NPN transistor is exactly opposite to the PNP transistor.  The NPN transistor contains three terminals which are same as the PNP transistor. W hich are Emitter , Collector , and Base.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Operation of The NPN Transistor The positive supply is given to the collector terminal. The negative supply to the emitter terminal with a resistor either the emitter or collector or emitter circuit.  To the base terminal the voltage is applied and it operated as an ONN/OFF state of a transistor.  The transistor is in OFF state when the base voltage is same as the emitter. 

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Operation of The NPN Transistor  If the base voltage is increased with respect to the emitter then the transistor mode is in ON state . By using this condition the transistor can act like both applications which are amplifier and switch . The basic symbol and the NPN configuration diagram as shown.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Hetero Bipolar Junction The Hetero bipolar junction transistor is also a type is the bipolar junction transistor . It uses different semiconductor materials to the emitter and base region and produces hetero junction . The HBT can handle the singles of very high frequencies of several hundred GHz. It is used in ultrafast circuits and mostly used in radio frequency. 

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Application of Hetero Bipolar Junction Used in Cellular Phones. Used in RF Power Amplifiers .

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Working Principle of BJT The BE junction is a forward bias and the CB is a reverse bias junction.  The width of the depletion region of the CB junction is higher than the BE junction.  The forward bias at the BE junction decreases the barrier potential. P roduces electrons to flow from the emitter to the base. The base is a thin and lightly doped it has very few holes and less amount of electrons from the emitter.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Working Principle of BJT A bout 2% it recombine in the base region with holes and from the base terminal it will flow out . This initiates the base current flow due to combination of electrons and holes.  The left over large number of electrons will pass the reverse bias collector junction to initiate the collector current .

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Working Principle of BJT By using Kirchhoff Laws  we can observe the mathematical equation. I E  = I B  + I C The base current is very less as compared to emitter and collector current. I E  ~ I C Here the operation of PNP transistor is same as the NPN transistor. The only difference is only holes instead of electrons.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Working Principle of BJT

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Advantages of BJT High driving capability. High frequency operation. Digital logic family has an emitter coupled logic used in BJTs as a digital switch. There is low forward voltage drop.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Disadvantages of BJT It has a very complex base control. Hence , it may lead to confusion and hence, requires skilful handling.

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Applications of BJT Following are the two different types of applications in BJT they are Switching Amplification

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http://www.elprocus.com/ Bipolar Junction Transistors Working Principle and Applications Conclusion Bipolar junction transistors are “ Current Operated Devices ”. This Presentation gives the information about what is a bipolar junction transistor , Types of BJT, advantages, applications and characteristics of the bipolar junction transistors. Hope the given information in the Presentation is helpful to give some good information and understanding the project.

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