Full Form of BJT

A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. William Shockley, Bardeen, and W.H. Brattin are the discoverers of BJT.

In contrast, a unipolar transistor uses just one kind of charge carrier, similar to a field-effect transistor. By allowing a small current to be injected at one of its terminals to regulate a much larger current flowing between the terminals, a bipolar transistor can be used for switching or amplification.

BJTs utilise two p-n junctions between n-type and p-type semiconductor areas within a single crystal of material. A variety of techniques can be used to create the junctions, including doping the semiconductor material as it grows, depositing metal pellets to create alloy junctions, and diffusing n- and p-type doping materials into the crystal.

Voltage, current, and charge control

You can think of the base-emitter current (current control) or base-emitter voltage as controlling the collector-emitter current (voltage control). The base-emitter junction's current-voltage relation, which is the typical exponential current-voltage curve of a p-n junction, connects these viewpoints (diode).

Collector current is explained by the gradient of minority carrier concentration in the base area. Due to low-level injection, where there are much less excess carriers than usual majority carriers, the excess minority carriers really control the ambipolar transport rates, in which the surplus majority and minority carriers flow at the same rate.

Bipolar Junction Transistor Configuration

• A bipolar junction transistor has three terminals, with one terminal serving as both the output and the input, therefore there are three ways to connect it in an electrical circuit. Each type of connection has a unique way of reacting to the input signals in a circuit.

• Both voltage and current gain are present in the common emitter configuration.

• The typical collector configuration gives a current gain but no voltage gain.

• The standard base arrangement has a voltage gain instead of a current gain.

The following table characteristics of several transistor configurations-

Uses of BJT

Bipolar junction transistors are utilized as switches, amplifiers, filters, and even oscillators as well. The following is a list of additional uses for bipolar junction transistors:

• BJTs are used as demodulators or as detectors.

• They are used in wave-shaping circuits which are known as clipping circuits.

• BJT is used in switching and logic circuits.