Here, ‘Isat’ is the saturation current and it is the highest quantity of current flow among the two terminals like emitter as well as collector once this transistor is connected in the saturation region. So this region is mainly used for the ON-state for a switch wherever In this region, the transistors both the junctions are connected in forwarding bias. The typical operation of this transistor happens within this region. The active region is also called a linear region which lies in between the two regions like the cutoff & the saturation. So, the active region can be mainly used for the purpose of amplification wherever this transistor performs like an amplifier through a gain ‘β’ with the following equation Here, the base current (Ib) is used to control the quantity of Ic (collector current). In this region, one junction is connected in a forward bias whereas the other one is connected in reverse bias. The operating of BJT can be done in three different regions like active, saturation, and cut-off. So, between these three junctions, the BE junction can be connected in forwarding bias & the BC junction is reverse biased. The emitter section is doped highly as compared to the remaining layers.īoth the layers like base and collector include the same concentrations of charge carriers. The flow of charge within a transistor is because of the charge carrier’s diffusion among the two sections which belongs to different concentrations of charge carriers. In NPN transistor, two semiconductor junctions are there which have a thin anode region doped with ‘P’ whereas PNP transistor includes two semiconductor junctions that include a thin cathode region doped with ‘N’. Working of BJTīipolar junction transistor is classified into two types namely PNP and NPN based on types of doping of the terminals. The BE junction shows high resistance as this junction can be connected in reversed bias. So, being the central part of the BJT will allow it to manage the charge carriers flow among emitter & collector terminals. The base terminal is the most lightly doped segment in the transistor. The base terminal is the center part among collector & emitter terminals which forms two PN junctions among them. In BJT, the emitter is the most heavily doped region. The base terminal is always reverse biased with respect to other terminals like emitter so that it can produce huge majority carriers. The emitter terminal emits the charge carriers like holes or electrons to the other two terminals. The arrow symbol on the emitter terminal is always there and the arrow direction will represent the current flow because of the charge carriers. The NPN and PNP transistors symbol representation can be done like the following. The BJT includes three terminals like base, Emitter, and Collector which are discussed in brief. The schematic symbols of the NPN and PNP BJTs include the following. The base (B) – region is slightly doped & it is extremely thin as compared to the emitter terminal that is heavily doped & the somewhat doped collector region. A wire lead unites to every region and these leads are branded with C, B & E for the collector, base, and emitter respectively. Similarly, once the pn-junction connects the base & the collector region then it is known as the BC-junction. When PN-junction connects the base and emitter region then it is known as BE-junction. In BJT, the term bipolar refers to the utilization of both the charge carriers like electrons and holes within the structure. In NPN, it includes two N-regions separated by one P-region whereas, in PNP, it includes two P-regions and separates with one N-region. Construction of Bipolar Junction Transistor These transistors are available in two types namely PNP and NPN and their physical structure is shown below. This transistor includes three layers namely base, emitter, and collector. So, the construction of BJT can be done through three doped semiconductor sections which are separated through two PN-junctions. The construction of BJT will determine its working characteristics.
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