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Table of contents
1.
Introduction
2.
What is a BJT?
3.
Working of BJT
4.
Types of BJT
5.
Strengths and weaknesses of using BJTs 
5.1.
Strengths
5.2.
Weaknesses
6.
What is a Mosfet?
7.
Working of Mosfet
8.
Types Of Mosfet
9.
Pros and cons of using Mosfets
9.1.
Pros
9.2.
Cons
10.
Difference between BJT and Mosfet
11.
Key Differences between BJT and MOSFET
12.
Which is Better Amplifier BJT or MOSFET?
13.
Frequently Asked Questions
13.1.
Why use a MOSFET instead of a transistor?
13.2.
What is an Enhancement MOSFET?
13.3.
Where do we use MOSFETs?
13.4.
What are the three advantages of MOSFET over BJT?
14.
Conclusion 
Last Updated: Mar 27, 2024

Difference between BJT and Mosfet

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Introduction

Hello Ninja, Are you confused about choosing between BJTs and Mosfets for your project? Well, You have Coding Ninjas as your guide.
The BJT and MOSFET are semiconductor devices used in electronics for amplification and switching. BJT controls current with voltage, while MOSFET controls current with an electric field, making them essential components in various electronic circuits.

The BJT is a bipolar junction transistor and MOSFET is a metal oxide semiconductor field-effect transistor. The three terminals of BJT are the emitter, base, and collector whereas the three terminals of MOSFET are: the source, gate, and drain.

difference between bjt and mosfet

This blog will discuss BJTs and Mosfets and their working principles. Further, we will list the differences between BJT and Mosfet, concluding which would be a better choice.

What is a BJT?

BJT (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.

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Working of BJT

The BJT works on the principle of minority carrier injection and conduction. The emitter-base junction is in a forward bias state whereas the collector-base junction is reverse biassed. 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.

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.

PNP BJT

Also see, Difference Between Verilog and Vhdl

Strengths and weaknesses of using BJTs 

The strengths and weaknesses of BJTs are:

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.

enhancement mosfet

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

depletion mosfet

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.

Difference between BJT and Mosfet

The difference between BJT and Mosfet are:

BJT

MOSFET

The full form of BJT is Bipolar Junction Transistor. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor.
BJT is made up of three layers, the emitter, base, and collector. Mosfet consists of a gate, a source, and a drain.
BJT’s collector current is controlled by the current flowing into the base terminal. In Mosfet, the voltage applied to the gate controls the current flowing through the source and the drain.
It is a bipolar electronic device. It is a uni-polar electronic device.
BJTs have a negative temperature coefficient. Thus they do not have good thermal stability. Mosfets have a positive temperature coefficient, thus having better thermal stability.
Chances of breakdown are more in BJTs Mosfets have lesser chances of a secondary breakdown.
BJTs have slower switching speeds. Mosfets have a faster switching speed.
BJTs have low impedance. Mosfets have high impedance.
BJTs are affected by noise easily. Mosfets have better noise immunity.
BJTs are comparatively cheaper. Mosfets are costly.
Used in electronic circuits where low current is required. Used in electronic circuits where high power is required.

Key Differences between BJT and MOSFET

Below are the 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 whereas MOSFETs are faster.
     
  • Power consumption: BJTs consume more power and MOSFETs consume less power.
     
  • 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.

Frequently Asked Questions

Why use a MOSFET instead of a transistor?

MOSFETs are used instead of transistors because they are faster, more efficient, more temperature-stable, and easier to drive. This makes them ideal for a wide range of applications.

What is an Enhancement MOSFET?

Enhancement Mosfet is a Metal Oxide Semiconductor Field Effect Transistor type that requires positive gate voltage to create a conducting channel between the source and the drain. It remains OFF under normal conditions.

Where do we use MOSFETs?

Mosfets are used in high switching speed and low power consumption applications. Mosfets are widely used as a switch or amplifiers in power electronics, integrated circuits, and digital logic circuits. They are typically useful in computers, smartphones, televisions, etc.

What are the three advantages of MOSFET over BJT?

The three main advantages of MOSFET over BJT are that they have higher input impedance, lower on-resistance and are less sensitive to temperatures. This makes them ideal for a wide range of applications.

Conclusion 

Kudos, Ninja, on making it to the finish line of this article! BJTs and Mosfets are two different transistors used for amplification in electronic circuits. Although they are both three-terminal devices, the difference between BJT and Mosfet cannot be ignored.

We hope this blog was useful to you in understanding the key difference between BJT and MOSFET. Do not stop learning! We recommend you read some of our other Unix articles: 

1. Logic Gate and circuits

2. Current sensors

3. Sequential circuit

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