Learn the difference between BJT and Mosfet

 BJT and MOSFETS are a very widely popular transistors  and are used in most electronic devices to know the difference between them and their applications first we have to know about what are transistors and how these semiconductor devices work.

What are semiconductor devices?

Semiconductor devices are electronic components that utilize the properties of semiconductor materials to control the flow of electric current. These devices are crucial building blocks in modern electronics and are found in a wide range of applications, including computing, telecommunications, power electronics, and consumer electronics.

Some common semiconductor devices include: Diodes, Transistors, Integrated Circuits (ICs), Optoelectronic Devices, Thyristors, MEMS (Micro-Electro-Mechanical Systems) Devices, and many more.

What is a transistor?

A transistor is a miniature semiconductor that regulates or controls current or voltage flow in addition amplifying and generating these electrical signals and acting as a switch/gate for them. Typically, transistors consist of three layers, or terminals, of a semiconductor material, each of which can carry a current.

When working as an amplifier, a transistor transforms a small input current into a bigger output current. As a switch, it can be in one of two distinct states -- on or off -- to control the flow of electronic signals through an electrical circuit or electronic device.

Why transistors are important?

On its own, a transistor has only one circuit element. In small quantities, transistors are used to create simple electronic switches. They are the basic elements in integrated circuits (ICs), which consist of a large number of transistors interconnected with circuitry and baked into a single silicon microchip.

In large numbers, transistors are used to create microprocessors where millions of transistors are embedded into a single IC. They also drive computer memory chips and memory storage devices for MP3 players, smartphones, cameras and electronic games. Transistors are deeply embedded in nearly all ICs, which are part of every electronic device.

Transistors are also used for low-frequency, high-power applications, such as power-supply inverters that convert alternating current into direct current. Additionally, transistors are used in high-frequency applications, such as the oscillator circuits used to generate radio signals.

What is a BJT?

BJT, or a Bipolar Junction Transistor, is an electronic device that is used to amplify and switch electronic signals in many electronic circuits. In this transistor, the current flow depends on the flow of charge carriers, electrons, and holes. 

It consists of three terminals, emitter, base, and collector. While the emitter and the collector have the majority of charge carriers, the base is lightly doped, thus controlling the terminal of the transistor. 

BJTs are often used in analog and digital electronics as amplifiers, oscillators, etc., in electronic circuits.

Working of BJT

The BJT works on the principle of minority carrier injection and conduction. The emitter-base junction is in a state of forward bias whereas the collector base junction is reverse biased. The forward bias permits the current to flow to the collector. Thus collector current is almost equal to that of emitter current.

Types of BJT

BJTs are made of either made of N-type or P-type semiconductor materials and thus can be categorized into two types:

NPN BJTs: When a P-type semiconductor is played between two N-type layers, the resulting BJT is known as an NPN BJT.

PNP BJTs: When a PNP structure is formed with the N-type semiconductor layer in the middle, the BJT formed is known as a PNP BJT.

Strengths and weaknesses of using BJTs 

Strengths

BJTs have several strengths in electronic applications:

• BJTs have a high life span. Thus they are preferred in applications where reliability is the first priority.
• BJTs have wide frequency response; that is, they have a large gain bandwidth.
• BJTs are less costly compared to other transistors.
• BJTs require simple biasing. Thus, they are easy to configure.

Weaknesses

The weaknesses of BJTs are:

• BJTs generally have higher power dissipation which leads to the loss of power
• BJTs have a lower switching speed
• The thermal stability of BJTs is less than that of Mosfet. Hence they are more sensitive to temperature. This is a major difference between BJT and Mosfet.
• BJTs have low input impedance. Thus, additional buffering is required. 
• It is less immune to noise.

What is a Mosfet?

Mosfet stands for Metal-Oxide Semiconductor Field Effect Transistor. It is a three-terminal electronic device that consists of a gate, a source, and a drain. It consists of a thin insulating layer of silicon oxide. 

The transistor works on the principle of field effect modulation of the conductivity of a semiconductor channel. The voltage applied at the gate terminal controls the functionality of the Mosfet.

Mosfets are widely used as a switch or amplifiers in power electronics, integrated circuits, and digital logic circuits. They are typically a very useful component in computers, smartphones, televisions, etc.

Working of Mosfet

The working of a Mosfet is based on the voltage applied to the gate, source, and drain terminals. This voltage establishes an electric field across the insulating silicon oxide layer, which in turn changes the conductivity of the channel. This either allows or blocks the flow of charge carriers between the source and the drain, depending on the type of Mosfet used.

Types Of Mosfet

Mosfets can be categorized into two types depending on the operational feature.

Enhancement Mosfet: Enhancement Mosfet is a type of Mosfet that requires positive gate voltage to create a conducting channel between the source and the drain. It remains OFF under normal conditions.

Depletion Mosfet: The Depletion Mosfet is normally ON and conducts current without the need for any external voltage at the gate terminal.

Pros and cons of using Mosfets

The pros and cons of using Mosfets are:

Pros

• The pros of using Mosfets are.
• The switching frequency of Mosfets is very high.
• Mosfets consume less energy.
• Mosfets have high thermal stability and hence can handle high voltage levels
• Mosfets are comparatively easier to manufacture.
• Mosfets can be easily scaled down, thus making them suitable for compact circuits.

Cons

The cons associated with using Mosfet are as follows:

• Mosfet has a very short lifespan.
• Repeated calibrations are to be done for error-free measurement.
• Mosfets are sensitive to overvoltage, which may result in breakdown or failure.
• Electrostatic Discharge can cause damage to the Mosfets.
• Next, we will be discussing the difference between BJT and Mosfet.

Key Differences between BJT and MOSFET

Construction: BJTs are bipolar junction transistors, and MOSFETs are metal-oxide-semiconductor field-effect transistors. BJTs have three terminals: the emitter, base, and collector. MOSFETs have only three terminals: the source, gate, and drain

 

Operation: BJTs operate by controlling the flow of current between the emitter and collector, while MOSFETs control flow of current between the source and drain

 

Switching speed: BJTs are slower than MOSFETs

 

Power consumption: BJTs consume more power than MOSFETs

 

Temperature sensitivity: BJTs are more temperature-sensitive than MOSFETs

Which is Better Amplifier BJT or MOSFET?

There is a major difference between BJT and Mosfet. The choice between a Mosfet and a BJT depends on the requirements. Specific factors like voltage levels, power dissipation, switching speed, and cost must be considered before choosing between a Mosfet and a BJT.

Mosfets are used where high switching speed and low power consumption are required, while BJTs work better for high-current and low-voltage applications. Thus, evaluating all the specifications and requirements before making your choice is important.