How Many PN Junctions Does A Transistor Have

There are two types of Bipolar Junction Transistor(BJT) transistors: The NPN transistor and the PNP transistor. Where PNP stands for Positive-Negative-Positive and NPN stands for Negative-Positive-Negative. So a BJT transistor consists of 2 pn junctions.

A three-terminal semiconductor device called a bipolar junction transistor (BJT) can amplify or magnify a signal since it has two p-n junctions. A BJT is a device with current control. Emitter(E), Base(B), and Collector(C) are the three terminals on a bipolar junction transistor. Both electrons and holes are used as charge carriers in a junction transistor.

Working Of Junction Transistor

In the common base transistor configuration, the base of a transistor is made thinner and is lightly doped in comparison to the emitter and collector, meaning that the density of the majority carriers in the base is lower than the density of the majority carriers in the emitter and collector.

The emitter receives the current flow, which the collector then gathers. The base offers the interaction for the connectivity necessary for a proper connection between the emitter and the collector. The arrow of a junction transistor points in the direction of the common current flow. The arrow in the emitter of an n-p-n transistor points away from the base, whereas the arrow in the emitter of the p-n-p transistor points in the direction of the base. When a junction transistor is employed in a circuit, the base-emitter junction is typically forward biassed and the base-collector junction is reverse biased

Types Of Junction Transistors

Junction transistors come in two different varieties, and they are:

• The NPN transistor: In an n-p-n junction transistor, p-type charge carriers predominate in middle, while n-type charge carriers predominate at the other two ends.

• The PNP transistor: The majority charge carriers in a p-n-p transistor are p-type, while the minority charge carriers are n-type in the other two hands.

Examples Of Transistors

NPN Transistor

A p-type semiconductor base is sandwiched between an n-doped emitter and an n-doped collector in an NPN transistor. The most popular bipolar transistors are NPN transistors because electron mobility is easier than hole mobility.

The NPN transistor's design and symbol are depicted in the above figures. In an n-p-n transistor, electrons make up the majority of the charge carriers while holes make up the minority at both end terminals. Large current flows from the emitter to the collector as a result of a tiny amount of current at the base terminal. The majority of the charge carriers in the emitter of the transistor are attracted to the base due to forward biassing. The base region's electron-hole recombination is extremely modest because of the thin size of the base, and the majority of the electrons cross into the collector zone.

PNP Transistor

An n-type semiconductor base is positioned in a PNP transistor between a p-doped emitter and a p-doped collector. In this particular form of the transistor, holes make up the majority of the carriers while electrons make up the minority at both end terminals. The emitter to the base junction and base to the collector junction of a PNP transistor is forward and reverse bias, respectively.