Types of Transistors

A transistor is a semiconductor device that may either magnify signals or operate as a switch that can be manipulated electrically. A transistor is a three-terminal device that allows a little current or voltage at one terminal (or lead) to regulate a substantial current flow between the other two terminals (leads).

Vacuum tubes have been replaced with transistors for a long time since transistors have more advantages than vacuum tubes. Transistors are compact in size, use little energy to operate, and dissipate very little power. One of the most significant active components is the transistor (a device which can produce an output signal higher power than that in the input signal).

Transistors are used in practically all electronic circuits, including amplifiers, switches, oscillators, voltage regulators, power supplies, and, most crucially, digital logic integrated circuits.

Type of transistors

A transistor is a semiconductor device that can be used to boost or switch electronic signals. Bipolar transistors (bipolar junction transistors: BJTs), field-effect transistors (FETs), and insulated-gate bipolar transistors are the three types of transistors (IGBTs).

A bipolar transistor is one that employs both electrons and holes as charge carriers. There are two types of bipolar transistors: npn and pnp.

A field-effect transistor is a unipolar device that does not have a pn junction in the main current path. There are two types of field-effect transistors: N-channel and P-channel.

A voltage-driven MOSFET is followed by a high-current transistor in an IGBT.

Bipolar transistors

They are of 2 types:

1. Bipolar transistor (BJTs)

2. Bias Resistor Built-in Transistor (BRTs)

Bipolar transistor (BJTs)

Bipolar Junction Transistors are a type of junction transistor (BJT) The term ‘bipolar’ alludes to the fact that current conductivity requires both electrons and holes, while the term ‘junction’ relates to the presence of PN Junction (two junctions, in fact).

Emitter (E), Base (B), and Collector (C) are the three terminals of a BJT (C). Depending on their structure, BJT transistors are classified as NPN or PNP transistors.

The input current to the base terminal is the sole thing that turns the Bipolar Junction Transistors on. BJTs can work in three different environments. They are as follows:

• Cut-off Region: The transistor is in the ‘OFF’ state, which means there is no current flowing through it. It’s essentially a toggle switch.

• In the active region, the transistor acts as an amplifier.

• Saturation Region: The transistor is fully ‘ON’ and also acts as a closed switch in this region.

                                               Bipolar transistor (npn)

FET (Field Effect Transistor)

Another common form of transistor is the Field-Effect-Transistor (FET). The FET has three terminals in general (like BJTs). Gate (G), Drain (D), and Source (S) are the three terminals (S). The two varieties of Field Effect Transistors are Field – Effect Transistors (JFET) and Insulated Gate Field Effect Transistors (IG-FET), also known as Metal Oxide Semiconductor Field Effect Transistors (MOSFET).

We also consider a fourth terminal, termed Base or Substrate, for the circuit’s connections. The size and geometry of a channel between Source and Drain, which is created by voltage applied at the Gate, is controlled by FETs.

Field Effect Transistors are unipolar devices since they only need the majority of charge carriers to function (unlike BJT, which are bipolar transistors).

JFET (Junction-Field Effect Transistor)

The JFET (Junction-Field-Effect Transistor) is the simplest and oldest type of Field Effect Transistor. Switches, amplifiers, and resistors are all used with JFETs. This is a voltage-controlled transistor. 

The voltage placed between the transistor’s gate and source controls the flow of electric current between the transistor’s source and drain. JFET transistors come in two varieties: N–Channel and P–Channel.

MOSFET

The most common and popular type of transistor is the Metal Oxide Semiconductor Field Effect Transistor (MOSFET). A small layer of metal oxide separates the Gate region and the channel, as indicated by the name ‘Metal Oxide’ (usually, SiO2).

Because the Gate region is totally insulated from the Source – Drain region, MOSFET is also known as Insulated Gate FET. The primary Semiconductor (Silicon) in which the FET is constructed has an extra terminal called substrate or body. The drain, source, gate, and body or substrate are the four terminals of the MOSFET.

MOSFETs have a number of benefits over BJTs and JFETs, the most notable of which is that they have a high input impedance and a low output impedance. It is a key component in Integrated Circuit design technology and is applied in switching and power circuits.

Conclusion

Transistors have become an indispensable component of modern electronics, and we cannot envision a world without them. We will learn about the classification and different types of transistors in this tutorial. Based on their uses, we shall learn about BJT (NPN and PNP), JFET (N-Channel and P-Channel), MOSFET (Enhancement and Depletion), and Transistors (Small Signal, Fast Switching, Power, etc.).