What is a Transistors? | Types of Transistors, Working & Uses

What is a Transistor in Electronics? | Definition

A semiconductor device called a transistor has the ability to switch or amplify electronic signals. It is a significant electronic invention that consists of an emitter, a base, and a collector constructed of semiconductor materials like silicon or germanium.

The most typical type of transistor, along with NPN (negative-positive-negative) and PNP (positive-negative-positive) transistors, is the bipolar junction transistor (BJT). Transistors work by regulating the voltage applied to the base terminal to the electric current flowing between the emitter and collector terminals. NPN transistors can act as amplifiers by boosting weak input signals into stronger output signals.

By adding a voltage to the base terminal, transistors can also function as electronic switches. When turned on, they function as a closed switch by allowing current to pass between the emitter and collector. When turned off, they operate as an open switch by obstructing the flow of current. The foundation of binary logic, which is utilized in computers and other digital devices, is this switching capability, which is essential in digital electronics. Many thousands (or perhaps millions) of logic gate circuits make up microcontrollers, and microprocessors can have up to 100 million gates. More potent and compact electronic gadgets are now possible thanks to miniaturization and the integration of several transistors onto a single semiconductor chip. Computers, cellphones, televisions, radios, and many more electrical devices all use transistors. To sum up, transistors are a crucial part of contemporary electronics since they make it possible to switch and amplify electronic signals and they also spur the creation of more potent and compact electronic gadgets.

Types of transistors | Classifications

What are NPN and PNP types of transistors?

Transistors come in a variety of varieties, each having unique properties and uses. The most prevalent types are field-effect transistors (FETs) and bipolar junction transistors (BJTs). 

NPN and PNP are the two varieties of BJTs, both of which are constructed from three layers of semiconductor material. An NPN transistor’s base terminal receives a modest current that regulates a larger current flow between the emitter and collector. The current moves in the opposite direction in a PNP transistor. BJTs are frequently utilized in audio and radio frequency applications and can be employed as switches or amplifiers. JFET and MOSFET are the two varieties of FETs.

NPN Transistor

A bipolar junction transistor (BJT) with three layers of semiconductor material is known as an ‘NPN transistor’. A layer of p-type semiconductor material is sandwiched between two layers of n-type semiconductor material and the NPN transistor is made up of an emitter, a base, and a collector.

When a little current runs into the base terminal of an NPN transistor, the little input signals are amplified to create bigger output signals. By adding a voltage to the base terminal, they can be utilized as electronic switches as well. When turned on, they function as a closed switch by allowing current to pass between the emitter and collector. They prevent current flow when turned off. Electronic circuits like amplifiers, oscillators, and digital logic circuits frequently employ NPN transistors. Because of their high gain and low noise qualities, they are frequently employed in audio and radio frequency applications.

PNP Transistor

Bipolar junction transistors (BJTs), which include three layers of semiconductor material, is known as ‘PNP transistor’. A layer of n-type semiconductor material and two layers of p-type semiconductor material sandwich the emitter, base, and collector layers.

When a tiny current comes out of the base terminal of PNP transistors, small input signals are amplified to create bigger output signals. By adding a voltage to the base terminal, they can be utilized as electronic switches as well. They function as a closed switch when turned on, blocking the current passage between the emitter and collector terminals when turned off. PNP transistors are frequently found in electronic circuits such as switching circuits, power regulators, and audio amplifiers. Due to their large current capacity and low power consumption, they are widely used in industrial and automotive applications.

NPN Transistor vs. PNP Transistor | Comparision

What are the difference between NPN and PNP?

The comparison of NPN vs. PNP Transistors is given in tabular form. Let’s study,

#NPN TransistorPNP Transistor
01The transistor flips OFF and doesn’t operate across the collector terminal when the base current is lowered.A PNP transistor turns OFF when its base has a current flowing through it.
02From the collection terminal to the emitter terminal, the current flows.From the emitter to the collector terminal, the current flows.
03As the current in the base terminal rises, the transistor turns ON.When there is no current flowing at the base terminal, the transistors turn ON.
04The two N-type semiconductors are surrounded by one P-type semiconductor.It is constructed of two P-type material layers with an N-type layer in the middle.
05By maintaining a +ve voltage in the collector, the current is produced there.By maintaining a +ve voltage at the emitter terminal, current is created from the emitter to the collector.

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JFET Transistor

The Junction Field Effect Transistor (JUGFET or JFET) lacks PN-junctions in favor of a narrow, high resistivity semiconductor “Channel” made of either N-type or P-type silicon, with two ohmic electrical connections at either end that are known as the Drain and the Source, respectively. N- channel and P-channel junction field effect transistors are the two fundamental JFET designs. The channel of an N-channel JFET is doped with donor impurities, causing electrons to flow through the channel negatively (hence the name N-channel).

MOSFET Transistor

MOSFETs (metal-oxide-semiconductor field-effect transistors) have completely changed the electronics industry thanks to their exceptional performance and wide range of uses. The MOSFET transistor is a pillar of contemporary electronics, powering a wide range of items from cellphones and computers to automobiles and equipment used in space research.

A source, drain, and gate make up the three terminals of a MOSFET, a semiconductor device. Its basic structure comprises of a silicon dioxide (SiO2)- or silicon dioxide-based thin insulating layer separating the semiconductor channel from a metal gate electrode. MOSFETs function as voltage-controlled devices because of the way the gate voltage and the charge carriers in the channel interact to regulate the current flow.

JFET vs. MOSFET | Comparision

What are the difference between JFET and MOSFET?

01JFET manufacturing is a straightforward procedure.MOSFET manufacturing is a complicated process.
02The high input capacitance of these makes them less prone to damage.Due to the metal oxide insulator, these are more prone to damage.
03Having three terminals, a JFET is a three-terminal semiconductor device.A four-terminal semiconductor device is a MOSFET (Metal-Oxide-Semiconductor Field- Effect Transistor).
04It is only capable of operating in depletion mode.It is capable of both depletion and enhancement.
05As a result of their high input impedance, which is on the order of 1010 ohms, they are more susceptible to input voltage signals.Because it provides an even higher input impedance than JFETs, they are more resistive.
06It permits a gate leakage current of about 10-9A.While MOSFETs will have a gate leakage current of the order of 10–12 A.
07For low noise applications, these are perfect.These are typically employed in noisy applications.

How does a transistor work?

Electronic devices known as transistors use the principles of semiconductors to regulate the flow of electricity. The bipolar junction transistor (BJT), which is the most popular kind, is made up of three layers of semiconductor material: the emitter, base, and collector. A little current in an NPN transistor controls a bigger current between the emitter and collector by flowing into the base terminal. The features of the semiconductor material affect the behavior. Electrons are injected into the base when a voltage is applied to the base-emitter junction, affecting the conductivity and enabling current to flow from the emitter to the collector.

Because of this characteristic, transistors can act as amplifiers, boosting weak input impulses to create stronger output signals. A modest control current can turn a transistor “on” or “off,” permitting or preventing the flow of current between the emitter and collector. Transistors can also function as switches.

Another typical type of transistor is a field-effect transistor (FET), which regulates an electric field to control the passage of current via a semiconductor channel. FETs are used in digital circuits because they use a gate terminal to control the flow of current in the channel. By providing downsizing, amplification, and switching capabilities, transistors revolutionized electronics and laid the groundwork for contemporary technology.

How many transistors are in a CPU?

Depending on the model and generation, a CPU’s (central processing unit) transistor count can change. Modern CPUs are incredibly intricate and transistor-heavy. High-end CPUs for consumer PCs can have tens of billions of transistors until September 2021. The numbers may have drastically altered since then, thus it’s crucial to keep in mind that transistor counts continue to rise with improvements in semiconductor technology.


Let’s sum up by saying that a transistor is an essential electronic component that works by regulating the movement of charge carriers through its three layers. It can be divided into various varieties, such as field-effect transistors (FETs) and bipolar junction transistors (BJTs), each of which has a different operating principle. It can enhance weak electrical signals by adjusting the voltage or current applied to the transistor’s base or gate terminal.

By taking a weak input signal and boosting its power and amplitude to a level appropriate for driving a load, transistors act as amplifiers. To achieve this amplification, a greater current voltage that is proportional to the input signal is controlled in the output circuit. Transistor-based amplifiers are widely utilized in a variety of fields, such as audio systems, telecommunications, and signal processing. They are essential for the processing, transmission, and exchange of signals and information, which makes it possible for a variety of electronic devices to communicate effectively and reliably. The capacity of the transistor to amplify signals has transformed technology and shaped the contemporary environment in which we live.

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