Table of Content

• What is a Transistor?
• Types of Transistors
• Bipolar Junction Transistor (BJT)
• Types of Bipolar Transistor
• Difference between NPN and PNP Transistor
• Configuration of BJT
• Unipolar Junction Transistor
• Field Effect Transistor
• Junction Field Effect Transistor
• MOSFET
• Insulated Gate Bipolar Transistors
• Avalanche Transistor
• Schottky Transistor
• Diffusion Transistor
• How Do Transistors Work?
• Transistors Operation
• Transistor Application

Characteristic	PNP Transistor	NPN Transistor
Majority Charge Carrier	Holes	Electrons
Current Flow Direction	Base to Emitter	Emitter to Base
Symbol Representation	Arrow points outward from the transistor	Arrow points inward toward the transistor

Configuration of BJT

Bipolar Junction Transistor works in three configurations which are mentioned below:

Common Emiiter: In CE configuration, the emitter terminal of the transistor is common between input and output terminal of the transistor.

Common Base: In CB configuration, the Base terminal of the transistor is common between input and output terminal of the transistor.

Common Collector: In CC configuration, the collector terminal of the transistor is common between input and output terminal of the transistor.

Unipolar Junction Transistor

Unipolar Junction Transistors, commonly referred to as field-effect transistors (FETs), work by managing the movement of either electrons or holes. This category comprises Metal-Oxide-Semiconductor FETs (MOSFETs) and Junction Field Effect Transistors (JFETs).

FETs consist of gate, source, and drain components, acting as gatekeepers controlling current flow. FETs can be NPN or PNP, affecting current based on silicon layer arrangements.

Voltage applied to the gate generates an electric field. N-channel FETs allow electron flow, while P-channel facilitates hole movement. This effect turns the transistor on/off or governs current flow.

BJTs manage the movement of both electrons and holes, while FETs regulate current using electric fields. Both have distinct applications: BJTs are efficient for signal amplification and switching, while FETs excel in low-noise amplification, buffering, and analog switches.

Field Effect Transistor

Field-Effect Transistor (FET) is a type of transistor that utilizes an electric field to control the conductivity of a semiconductor channel. FETs are widely used in electronics for various applications including amplification and switching.

There two common types of FETs are

• Junction Field Effect Transistor
• Metal Oxide Semiconductor Field Effect Transistor

Let’s discuss these transistor in detail.

Junction Field Effect Transistor

A Junction Field Effect Transistor (JFET) serves as a distinct transistor type, mainly employed for amplifying low-power signals. The operation of JFETs involves regulating the current between the source and drain terminals through the influence of an electric field. The voltage applied to the gate terminal regulates the conducting channel width, controlling the current flow. Commonly used in audio preamplifiers and oscillators, JFETs offer high input impedance and its various applications are in signal amplification scenarios.

There are two types of JFET namely N-channel JFET and P-Channel JFET. The symbol for these two types are shown below:

MOSFET

Metal-Oxide-Semiconductor Field-Effect Transistor commonly called MOSFETs are the most widely used type of FETs in modern electronics. They have a metal gate insulated from the semiconductor channel by a thin layer of oxide (usually silicon dioxide). The conductivity of the channel is controlled by the voltage applied to the gate terminal. MOSFETs are also available in two main types: N-channel MOSFETs and P-channel MOSFETs.

Insulated Gate Bipolar Transistors

Insulated Gate Bipolar Transistor (IGBT) is a specific kind of transistor. Notably, it has traits from two different types of transistors, namely the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and bipolar transistors.

• IGBTs find frequent applications in high-power scenarios like motor drives and power inverters.
• The combination of the different gates provides low on-state voltage drop, making IGBTs crucial in power electronics.
• They offer efficiency and controlled power switching, proving invaluable in applications requiring high voltage and current handling capabilities, such as motor drives and industrial power control systems.

Avalanche Transistor

Avalanche Transistor is a specialized type of bipolar junction transistor (BJT) that operates in the avalanche breakdown region. In a standard BJT, the transistor operates primarily in the active region, where the collector-base junction is reverse-biased and the collector current is controlled by the base current.

However, in an avalanche transistor, the transistor is deliberately operated in the avalanche breakdown region of its collector-base junction. When a high reverse voltage is applied to the collector-base junction, it creates a strong electric field across the junction. If this reverse bias voltage exceeds a certain threshold, called the breakdown voltage or avalanche voltage, it can cause a phenomenon known as avalanche breakdown.

Schottky Transistor

Schottky Transistor combines the principles of a Schottky diode and a bipolar transistor into a single device. Like a Schottky diode, it has a metal-semiconductor junction instead of a traditional semiconductor-semiconductor junction. This metal-semiconductor junction forms a Schottky barrier, which has lower forward voltage drop and faster switching characteristics compared to a traditional P-N junction.

Diffusion Transistor

Diffusion Transistor is one of the early types of bipolar junction transistors (BJTs). In a diffusion transistor, the semiconductor material is doped to create regions of different conductivity types. These doped regions are known as the emitter, base, and collector. The emitter is heavily doped with either donor or acceptor impurities to create an excess of either electrons (N-type) or holes (P-type).

The base region is lightly doped and provides a path for the majority carriers (electrons or holes) to move between the emitter and collector. The collector region is also lightly doped and collects the majority carriers that flow through the base

How Do Transistors Work?

In a PNP transistor, ‘holes’ act as the primary charge carriers instead of electrons in an NPN transistor. This absence of electrons acts as positive charge carriers.

A PNP transistor comprises the emitter, base, and collector. Their functionality contrasts with an NPN transistor.

Emitter: Connected to a positive voltage source, it enables hole flow from the emitter to the base when a small current enters the base terminal.

Base: Acting as the control centre, the base permits holes to flow from the emitter towards the collector when it receives a small current. This base current manages a larger flow of holes from emitter to collector.

Collector: Linked to a more positive voltage than the base, the collector facilitates a larger hole current flow from the emitter, through the base, and to the collector.

In conclusion, when a small current enters the base, it regulates a larger flow of holes from the emitter to the collector. This operation parallels how an NPN transistor controls and amplifies currents, but with holes as the primary charge carriers.

Transistors Operation

Transistors are controllers for electricity. They’re like a sandwiches with layers that either have extra electrons (the n-type) or missing some electrons (the p-type). These layers decide how easily electricity can move through the transistor.

NPN Transistor Operation

In an NPN transistor, electrons can easily switch from one side (the base) to the other (the collector) with very minute voltage. The base deciding how many electrons get to pass through to the other side.

It works like a water valve which control how much water flows through a pipe. When the transistor is fully ‘on,’ it’s like opening that valve wide —electricity flows freely. When it’s ‘off,’ it’s like shutting that valve tight electricity stops. Transistors can also adjust the flow of electricity between fully ‘on’ and ‘off.’

In an NPN setup, when you make one part of the transistor a bit more positive than the other, it excites the electron to move. Electrons cleverly move from one side to the other, avoiding obstacles. The movement creates a current that powers the circuit which is connected to the transistor. So, transistors control electric flow with precision.

PNP Transistor Operation

In a PNP transistor setup, the layers in the transistor are now p-type (with extra electrons) and n-type (lacking some electrons).

In a PNP transistor, the base, control the movement of “holes” (missing electrons) from one side (the base) to the other (the collector) with the application of voltage. When the PNP transistor is fully ‘on,’ it permits a flow of electricity. Conversely, in the ‘off’ state, it tightly restricts the flow.

By making one part of the transistor more negative than the other. Holes moves adeptly, creating a current that energizes the connected circuit.

In summary, PNP transistors, is like a reverse NPN, offer precise control over the electric flow but operate with an inverted polarity, which shows the range of transistor technology.

Transistor Application

Transistor is generally used for following applications:

• Signal Amplification
• Digital Logic Circuits
• Oscillators
• Power Regulation

Apart from the above mentioned applications, transistors are used extensively in sectors of computers, as electronic switches and amplifier. Let’s learn these applications in detail

Transistor for Computers

In the realm of computing, transistors serve as foundational components within electronic circuits. Integrated circuits(ICs), the driving force behind computers, incorporate millions or even billions of these transistors. Their role involves both amplifying and controlling electrical signals, facilitating the processing and storage of information in a digital format. Its compact size and efficiency are pivotal factors that enable the existence of modern computing devices.

Transistor as a Switch

Beyond their foundational role, transistors also function prominently as electronic switches. Operating in this capacity, transistors regulate the flow of electrical current, akin to binary switches toggling between states of “on” or “off.” This binary functionality is fundamental to digital computing, where combinations of these on/off states represent and manipulate data.

Transistor as an Amplifier

Transistors are extensively used as amplifiers to increase the strength of electronic signals. In this role, they find applications in audio amplifiers, radio frequency circuits, and more.

Related Reads

• Difference between JFET and MOSFET
• Difference Between BJT and FET
• BJT Configurations

Transistor Types – FAQs

What is a Transistor and its type?

A transistor is a semiconductor device which not only governs the flow of current or voltage but it also amplifies in electronic circuits. They are mainly of two types: pnp transistor and npn transistor

What are PNP and NPN transistors?

PNP Transistor: has majority charge carrier as hole. NPN Transistor: has majority charge carrier as electron.

What is the Function of a transistor?

A transistor acts as an amplifier and a switch. It controls the flow of current and voltage in electronic circuits.

What are the Parts of a Transistor?

A transistor consists of three parts: the emitter, the base, and the collector.

What is a Transistor used for?

Transistors are used as switches and as amplifiers.

What are the types of Transistors?

There are two main types of transistors and they are: Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs).

What is FET transistor?

It works by controlling the flow of electric charge using an electric field.

Who developed Transistor?

The transistor was developed by three American physicists namely John Bardeen, Walter Brattain, and William Shockley.

What is the Purpose of Transistors?

The purpose of a transistor is to regulate the flow of current or voltage in electronic circuits.