TRANSISTORS

A transistor basic function is to control a larger electrical current or voltage by using a smaller one to act as either a switch or an amplifier. A transistor consists of three layers of a semiconductor material, typically silicon with each layer having a different electrical charge. The transistor has three terminals; the base, collector and emitter.

There are several types of transistors and they are; bipolar junction (BJT), field effect (FET), power, small signal, Darlington and insulated gate bipolar transistor.

Bipolar junction transistor (BJT) consists of three layers of semiconductor material (PNP or NPN). It has three terminals; basic, collector and emitter. The current flows from the collector to the emitter when a small voltage is applied to the base. Example of BJT includes; NPN (negative-positive-negative) and PNP (positive-negative-positive) transistors.

Field effect transistors (FET) consists of a channel of semiconductor material within three terminals; the source, gate and drain. The voltage applied to the gate controls the flow of current between the source and drain. Example of FET includes; junction field effect transistors (JFET), metal oxide semiconductor FET (MOSFET) and insulated gate FET (IGFET).

Power transistor is a type of BJT or FET designed to handle high currents and voltage for applications such as power supply, motor control and amplifiers.

Smaller signal transistor is a type of BJT or FET used for low power applications such as audio amplifier, radio frequency (RF) amplifiers and switching circuits.

Darlington transistor is a type of BJT that consists of two transistors connected in a specific configuration. It has high current gain and used in applications such as power supplies and motor control.

Insulated gate bipolar transistor (IGBT) is a type of power transistor that combines the advantages of BJTs and FETs. It has high current handling capability and is used in applications such as power supplies, motor control and automotive systems.

The advantages of transistors are; they are compact in size, thereby enabling miniaturization. Transistors consume low power with minimal energy loss. Transistors are highly reliable and have a long life span, regardless of operation conditions such as mechanical shock and vibration. Transistors are low cost and are mass produced easily and cheaply making them affordable for use in most equipment and electronics. Transistors are capable of fast switching speeds enabling high frequency operation which is critical for digital computing and communication. Transistors are scalable and can be packed onto a single chip in millions to billions to make microprocessors and other devices. Transistors generate low heat and its efficiency improves especially in cold environment. Transistors are versatile in function and application, they function as switches, amplifiers, oscillators and regulators across countless circuit types.

The disadvantages of transistors are; transistors are very sensitive to temperature variation, hence their performance characteristics vary accordingly. Transistors, especially MOSFETs are susceptible to damage from over voltage/electrostatic discharge (ESD). Transistors exhibit a non-linear behavior, thus they can introduce distortion in analog applications if not carefully biased. Individual transistors often need paralleling or specialized power packages for high power applications. Transistors parameter like gain can vary significantly even within the same part number. Transistors are prone to ionizing radiation, a prime concern in aerospace and military applications. Transistors performance degrades over long term use due to aging and degradation.

Transistors find widespread applications in the following; computing, where they are used in logic gates, microprocessors, memory chips etc.; communications, where they are used in RF amplifiers, signal mixers, oscillators in radio, smartphones, satellites etc.; power electronics, where they are used in voltage regulators, inverters, motor drives, battery management systems etc.; consumer electronics, where they are used in audio amplifiers, televisions, computers, household appliances etc.; automotive systems, where they are used in engine control units, electric vehicle inverters, sensor interfaces etc.; medical devices, where they are used in pacemakers, diagnostic equipment, imaging systems etc.; industrial automation, where they are used in motor control, robotics, process control systems etc.; renewable energy, where they are used in solar inverters, wind turbine power conversion systems etc.; aerospace and defense, where they are used in radar systems, satellite communication, guidance systems and so on.

The future of transistor is based on the advances and development of the following technologies; transistors will continue to shrink in size, enabling more transistors to fit on a single chip. 3D transistors such field in field effect transistors (F in FETs) and gate all around field effect transistors (FETs), will become more prevalent, allowing for increased current handling and reduced power consumption. Wide band gap transistors, such as SiC and GaN transistors will be widely used for high powered applications such as electric vehicles and renewable energy systems. Also quantum transistors will be developed for quantum computing applications, enabling faster and more secure computing. New materials, such as grapheme, nanowires and 2D materials will be used to create transistors with improved performance, power efficiency and thermal management.

 

SOURCES:

• Electronic devices and circuit theory by Ro bert L.Boylestad and Lousis Nashelsky.
• Transistor electronics by F.S Gowen and A.H.S Agell.
• Semiconductor physics and devices by Donald A. Neamen.
• Transistor circuits: Analysis and applications by A.G.B Robertson.
• Semiconductor device physics and technology by S.S Mahalik.