Introduction
Table of Contents
- 1 Introduction
- 2 What is BJT (Bipolar Junction Transistor)?
- 3 Construction of Bipolar Junction Transistor
- 4 Types of Bipolar Junction Transistor
- 5 Mode of Operation of Bipolar Junction Transistor
- 6 Advantages of Bipolar Junction Transistor
- 7 Disadvantages of Bipolar Junction Transistor
- 8 Application of Bipolar Junction Transistor
- 9 Conclusion
W. Brattain, W. Shockley and J. Barden has been discovering the transistor in 1947. The word ‘Transistor’ is procured from the word ‘Transfer’ and ‘Resistor’. The word relates to the operation of BJT which is used to transfer an input signal from a low resistance circuit to high resistance circuit.
What is BJT (Bipolar Junction Transistor)?
The BJT (Bipolar Junction Transistor) is a three terminals semiconductor layers which is consist of two P-N junction which is magnify or amplify signals. Basically, it is current control device. In BJT the terminals are base, emitter and collector.
A small amplitude signal is applied at a base terminal and is available in an amplified form at a collector of a transistor. This amplification is provided from the BJT. It does not require external DC power source to supply or carry out the amplification process.
Construction of Bipolar Junction Transistor
A BJT is a semiconductor layers that is constructed with three heavily doped semiconductor i.e. Base, Emitter and Collector separated by a P-N junction. It is manufactured in two types PNP and NPN and is available as separate components in large quantities.
The function of this types of transistors is used to amplify current. It makes them useful as amplifier and switches. It has wide application in electronic devices such as mobile phones, radio transmitters and industrial control etc.
Types of Bipolar Junction Transistor
There are two types of BJT:
- PNP Transistor
- NPN Transistor
1). PNP Transistor:
The PNP transistor is N-Type semiconductor which is sandwiched between the two P-Type semiconductors. The two P-Type semiconductor is act as collector and emitter respectively while the N-Type semiconductor acts as a base.
The current enters in transistor through emitter such that the base-emitter junction is forward biased and base-collector junction is reversed biased.
2). NPN Transistor:
The NPN transistor is P-Type semiconductor which is sandwiched between the two N-Type semiconductors. The two N-Type semiconductor is act as collector and emitter acts as a base.
Current entering in collector, emitter and base as a sign convention of positive while the current that leaves the transistor has a sign convention of negative.
Mode of Operation of Bipolar Junction Transistor
There are three operating regions of bipolar junction transistor:
- Active region: It is a region in which the transistor operated as an amplifier.
- Saturation region: In this region the transistor is fully on and operates has a switch like collector current is equal to saturation current.
- Cut-off region: In this region the transistor is fully off, and collector current is equal to a zero.
Parameters:
1). Current Gain: Current gain is the ratio of collector current to a base current.
2). Voltage Ratings: It allows maximum voltage across different junction.
3). Power Ratings: It allows maximum power the transistor can handle without damages.
Advantages of Bipolar Junction Transistor
- It has high current gain, which makes them suitable for applications which required signal amplification, like audio amplifiers and radio frequency (RF) circuits.
- As compared to other types of transistors, BJTs can switch on and off instantly, which makes them useful in high-speed digital circuits and switching applications.
- Basically, it has a low voltage drop over the collector-emitter junction when it has fully conducting as compared to other types of transistors such as MOSFETs.
- Generally, it has better temperature stability as compared to some other transistor types, and make sure consistent performance over a range of operating temperatures.
Disadvantages of Bipolar Junction Transistor
- It requires a continuous base current to remain in the “on” state, which results in high power consumption as compared to field-effect transistors (FETs), typically in low-power applications.
- It is sensitive to temperature fluctuation, and excessive heat can decrease their performance or even cause failure. Actual thermal management is necessary, mainly in high-power applications.
- It can initiate noise into circuits, basically at higher frequencies, due to factors like thermal agitation and random fluctuation in carrier concentrations.
- While it has a lower saturation voltage and operates them in the saturation region which can lead to non-linear behavior and may cause distortion in amplification applications if not satisfactorily managed.
Application of Bipolar Junction Transistor
- It is used in radio and audio frequency amplifiers.
- It acts has switch digital circuits.
- It forms the basis of oscillator in an electronic circuit.
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Conclusion
In this article, we have studied about the aspects in designing circuits and utilize BJT effectively in various electronics applications.
FAQ for Bipolar Junction Transistor (BJT)
What are the two types of Bipolar Junction Transistors (BJT)?
NPN and PNP are two main BJT types. NPN contain electrons as majority carriers and PNP contain holes. This contrast cause current flow and voltage polarity, which enable complementary roles in electronic devices.
What are key characteristics of Bipolar Junction Transistors (BJT)
It is used to exhibit amplification, current control, and switching capabilities. It is also used to amplify signals, regulate current between terminals, switch between states, crucial for various electronic applications.
What are the structure of a Bipolar Junction Transistor (BJT)?
A BJT is made up of three doped semiconductor regions: emitter, base, and collector. These regions form two PN junctions which is essential for operation. Emitters introduce to charge carriers, base controls flow, and collector collects majority carriers.