Bipolar Junction Transistor or BJT is a semiconductor device which is constructed with 3 doped semiconductor Regions i.e. Base, Collector & Emitter separated by 2 p-n Junctions. It is a type of transistor that uses both electron and hole charge carriers. This transistor is commonly known as Bipolar transistor or BJT.
Bipolar transistors are manufactured in two types, PNP and NPN, and are available as separate components, usually in large quantities. The prime use or function of this type of transistor is to amplify current. This makes them useful as switches or amplifiers. They have a wide application in electronic devices like mobile phones, televisions, radio transmitters and industrial control.
BJTs are of two types namely NPN and PNP based on doping types of the three main terminals. An NPN transistor consists of two semiconductor junctions that have a thin p-doped anode region and PNP transistor also consists of two semiconductor junctions that have a thin n- doped cathode region.
The flow of charge in a Bipolar transistor is due to the diffusion of charge carriers between the two regions belong to different charge concentrations. Regions of BJT are known as the base, collector, and emitter.
The emitter region is highly doped when compared to other layers. Both collector and base layers have the same charge carrier concentrations. Among these junctions, the base-emitter junction is forward biased, and base-collector junction is reverse biased. Forward biased means p-doped has it contains more potential than the n-doped side.
The base-emitter current is controlled by collector-emitter current. This conclusion is drawn by the current-voltage relation of the base-emitter junction. Collector current has a base region where minority carriers are concentrated.
Transistor models such as Glenn poon model is responsible for the distribution of the charge which explains the behaviour of a transistor.
Since Bipolar Junction Transistor is a three terminal device, there are three ways to connect it within an electric circuit while one terminal is the same for both output and input. Every method of connection responds differently to the input signals within a circuit.
|Characteristics||Common Base||Common Emitter||Common Collector|
|Power Gain||low||Very high||medium|
|Output impedance||Very high||high||low|
Q1. What is BJT?
Ans: BJT stands for bipolar junction transistor and is defined as a device in a solid state which uses electron and hole charge carriers. It uses two junctions between two semiconductor types, p-type and n-type
Q2. What are the types of bipolar junction transistors?
Ans: There are two types:
Q3. Who invented BJT?
Ans: BJT was invented by W.H Brattin, Bardeen and William Shockley.
Q4. What are the operating regions of BJT?
Ans: The operating regions of BJT are:
Q5. What are the applications of BJT?
Ans: Following are the applications of Bipolar Junction Transistor:
Q6. What happens if the transistor is not biased properly?
Ans: Following is the list of consequences if the transistor is not biased properly:
Q7. Why is collector always reverse biased with respect to a base?
Ans: In order to remove the charge carriers from the base-collector junctions, the collector is always reverse biased.
Q8. Why is the emitter forward biased?
Ans: The emitter is always forward biased because most of the charge carriers are supplied to the base.
Q9. Why is collector larger than the emitter and the base?
Ans: The collector is larger because it dissipates much power.
Q10. How can a BJT be used as an amplifier?
Ans: BJT is used as an amplifier by transferring the current from low impedance loop to high impedance loop.