Exploring the Difference between MOSFET and BJT Transistors

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Transistors are fundamental electronic components that have revolutionized the field of electronics.They act as the fundamental components of contemporary technology, allowing the development of potent computers, smartphones, and a myriad of other gadgets.
In this blog, we will delve into the difference between two commonly used types of transistors: MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and BJT (Bipolar Junction Transistor).

What is a Transistor in a computer?

A transistor is a basic electronic component that is essential to a computer's operation. It is a semiconductor device that has the ability to switch or amplify electrical and electronic signals. In order to control the flow of electric current and carry out various logical processes, transistors are widely utilized in computer circuits.


What is a MOSFET airsoft?



Metal-oxide semiconductor Field Effect Transistor is referred to as a MOSFET. The electronic component has three terminals: a gate, a source, and a drain. It is made up of a thin silicon oxide insulating layer. 


The transistor operates on the basis of field effect modulation of a semiconductor channel's conductivity. The Mosfet's operation is governed by the voltage applied at the gate terminal.


MOSFETs are used in airsoft to increase the electrical control and effectiveness of the trigger mechanism. The firing mechanism of conventional airsoft weapons is activated by mechanical switches, which can result in problems including arcing, contact wear, and inconsistent trigger response. By substituting an electronic switch for a mechanical switch, MOSFETs solve these issues.


How Small Can MOSFETs Get?

  • As semiconductor manufacturing technology has developed over the years, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) have consistently shrunk in size. The minimum feature size, or smallest dimension that can be dependably produced on a chip, is a common way to describe the size of MOSFETs.
  • According to Moore's Law, which asserts that the number of transistors on a chip doubles nearly every two years, the minimum feature size of MOSFETs has been gradually reducing. Innovations in lithography methods and semiconductor production procedures are to blame for this development.
  • Modern semiconductor manufacturing processes are currently based on 5-nanometer (nm) technology. This indicates that the minimum MOSFET feature size in these cutting-edge chips is approximately 5 nm.
  • It's crucial to remember that a MOSFET's size is not simply dependent on the minimum feature size. Its size is also influenced by other elements, including the integrated circuit's complexity, the number of layers, and the general architecture of the transistor.
  • To further reduce the size of MOSFETs, researchers and semiconductor manufacturers are always experimenting with new technologies and methods. This includes investigating other transistor architectures, such as nanowire and carbon nanotube transistors, and developing sophisticated lithography techniques, such as extreme ultraviolet (EUV) lithography.
  • It's important to note that the size of MOSFETs has physical boundaries. Quantum effects and leakage currents can pose serious problems at incredibly small sizes. To overcome these difficulties and retain MOSFETs' performance and dependability as they get smaller, new materials and creative methods are needed.


In conclusion, MOSFET size has decreased over time, and current state-of-the-art technology is based on 5-nanometer technology. Although continuing research and development is focused on pushing the boundaries of downsizing while tackling the difficulties posed by decreasing transistor sizes, the size of MOSFETs is not primarily dictated by the minimal feature size.


What does BJT stand for?



A BJT, or a bipolar junction transistor, is a type of electrical component used in many electronic circuits to switch and amplify electronic signals. The passage of charge carriers, electrons, and holes affects the current in this transistor. 


The emitter, base, and collector are its three terminals. The base of the transistor is only minimally doped, controlling the terminal of the transistor while the emitter and collector have the majority of charge carriers. 


How does a MOSFET work?

How does a MOSFET work?


  1. Bias of the Substrate: The MOSFET is constructed on a silicon-based semiconductor substrate. The substrate is biased to a particular voltage, commonly referred to as the body bias or substrate bias. The MOSFET's correct operation is ensured by this biasing.
  2. Source and Drain: The source and drain regions in the semiconductor substrate are doped regions. Normally, the drain is connected to the load or the regulated component, whereas the source is connected to the ground or a common reference point.
  3. Gate: A metal electrode known as the "gate" is situated between a semiconductor substrate and an insulating layer called the "gate oxide." Between the source and drain regions, the gate electrode regulates the current flow.
  4. Channel Formation: The gate oxide functions as an insulator when no voltage is supplied to it, obstructing the flow of current between the source and drain. However, when a positive voltage is given to the gate, an electric field is produced that either attracts or repels positively and negatively charged carriers (holes and electrons, respectively) in the semiconductor substrate.
  5. Enhancement Mode: When a positive voltage is applied to the gate of an enhancement-mode MOSFET, an electric field is produced that draws electrons to the substrate's surface and forms a conductive channel between the source and drain regions. Current can move through this conduit from the source to the drain.
  6. Depletion Mode: In a depletion-mode MOSFET, applying a negative voltage to the gate generates an electric field that exhausts the channel's available carriers and lowers the conductivity. The MOSFET is ordinarily conducting in this state, and providing a positive voltage to the gate disables it.
  7. Gate Control: The conductivity of the channel may be regulated by adjusting the voltage applied to the gate, which enables the MOSFET to function as a switch or an amplifier. The MOSFET activates and allows current to flow between the source and drain when the gate voltage rises beyond a predetermined threshold. The MOSFET is turned off and the current flow is stopped when the gate voltage drops below the threshold.


It is crucial to remember that MOSFETs can be either N-channel or P-channel, depending on the electrons or holes that the gate voltage controls. When it comes to N-channel MOSFETs, where the channel is created by drawing electrons to the substrate's surface, the aforementioned operating principles are applicable. P-channel MOSFETs function similarly, however, they have the opposite polarity.


In conclusion, the development or depletion of a conductive channel in the semiconductor substrate regulates the current flow between the source and drain regions in a MOSFET. The MOSFET can act as a switch or an amplifier depending on the channel conductivity, which is controlled by the gate voltage.


How does a BJT work?

How does a BJT work?


  1. Biasing: Applying the proper voltages to the emitter, base, and collector regions of the BJT causes it to be biased. often, the collector is connected to a greater positive voltage, while the emitter is often coupled to a more negative potential. To regulate the behavior of the transistor, the base voltage is regulated with respect to the emitter and collector voltages.
  2. Emitter-Base Junction: A forward-biased pn-junction characterizes the emitter-base junction. The majority of charge carriers (holes in a PNP transistor or electrons in an NPN transistor) can move from the emitter region to the base region when a positive voltage is given to the emitter with respect to the base.
  3. Base Region: In comparison to the emitter and collector regions, the base region is incredibly thin and barely doped. It serves as the transistor's control area. A tiny amount of the current (the base current) goes into the base area when it passes through the emitter-base junction.
  4. Base-Collector Junction: The base-collector junction is one such junction. A depletion region is formed in the base-collector junction when a positive voltage is supplied to the collector with respect to the base. This region prevents the bulk of charge carriers from moving from the base to the collector.
  5. Transistor Modes: The BJT can function in cutoff, active, and saturation modes.
  • Cutoff Mode: When the transistor is in cutoff mode, no current passes through it because the base-emitter junction is reverse-biased. Effectively, the transistor is off.
  • Active Mode: Current can move from the emitter to the base when the base-emitter junction is forward-biased. With the collector current being inversely proportional to the base current, the transistor functions as an amplifier.
  • Saturation Mode: During saturation mode, both the base-collector and base-emitter junctions are forward-biased. This makes the transistor function as a closed switch and permits a significant current to flow from the collector to the emitter.
  1. Amplification: Signal amplification is possible when the BJT is operating in active mode. A signal is amplified as a result of the modest base current driving a considerably greater collector current. BJTs are well suited for uses in circuits including amplifiers, switches, and digital logic because of this characteristic.

It's vital to remember that depending on the majority of charge carriers, BJTs can either be NPN (with N-type semiconductor material) or PNP (with P-type semiconductor material). In NPN transistors, where electrons make up the majority of the charge carriers, the aforementioned operating principles are applicable. PNP transistors function similarly but with the polarity reversed.

In conclusion, a BJT functions by regulating the movement of current through the base area, which connects the emitter and collector regions. While the base-collector junction is reverse-biased to regulate the behavior of the transistor, the base-emitter junction is forward-biased to allow current passage. Depending on the biasing and operating conditions, the BJT can act as a switch or an amplifier.


Difference between MOSFET and BJT

  • The BJT (current-controlled) is a bipolar junction transistor, whereas the MOSFET (voltage-controlled) is a metal-oxide-semiconductor.
  • Despite having three terminals each, these are different. In contrast to the BJT, which has a base, emitter, and collector, the MOSFET has a source, drain, and gate.
  • A MOSFET depends on the voltage at the oxide-insulated gate electrode while a BJT depends on the current at its base terminal.
  • The construction of a MOSFET is naturally more complicated than that of a BJT.
  • MOSFET is utilized for high-power applications, while BJT is used for low-current applications.
  • Modern analog and digital circuits tend to use MOSFETs more frequently than BJTS.
  • The MOSFET is a voltage-controlled device, whereas the BJT is a current-controlled device.


Video related to the Difference Between MOSFET and BJT


Advantages and disadvantages of MOSFET and BJT

Advantages of MOSFET and BJT

Advantages of MOSFET

  • It's easy to manufacture.
  • It allows for quick operation.
  • Compared to JFET, it is more commonly utilized.
  • Digital circuitry uses MOSFETs of the enhancement kind.
  • MOSFET drain resistance is high due to low channel resistance.
  • Low power consumption allows for more components to be placed outside of the region on each chip.
  • It lacks a gate diode, making it possible to operate through a positive or negative gate voltage.


Advantages of BJT

  • High Current Gain: The current gain, or beta () value, of BJTs is high. BJTs are thus excellent for applications requiring the amplification of weak signals since a tiny base current may drive a greater collector current.
  • Low Saturation Voltage: When used in the saturation area, BJTs have a low saturation voltage. This enables effective switching and lowers power dissipation in devices like motor drivers and power amplifiers.
  • Robustness: Compared to MOSFETs, BJTs are often more robust and can withstand higher current and voltage levels. They are less vulnerable to damage from voltage spikes or electrostatic discharge and can handle larger power dissipation.
  • Simple Biasing: In comparison to MOSFETs, BJTs have a simpler biasing technique. They can be used more easily in some applications because they don't need a gate voltage or intricate biasing networks.
  • Temperature Stability: When compared to MOSFETs, BJTs exhibit greater temperature stability. They are suitable for applications that demand reliable performance over a wide temperature range since their characteristics are less impacted by temperature fluctuations.


Disadvantages of MOSFET and BJT

Disadvantages of MOSFET

  • The lifespan of a mosfet is quite brief.
  • The Mosfets may sustain damage from electrostatic discharge.
  • For error-free measurement, many calibrations must be carried out.
  • Overvoltage can cause a breakdown or failure in mosfets since they are susceptible to it.


Disadvantages of BJT

  • It is less noise-resistant.
  • BJTs switch at a slower rate. 
  • The input impedance of BJTs is low. As a result, more buffering is needed. 
  • BJTs typically dissipate more power, which results in power loss. 
  • BJTs are less thermally stable than Mosfets are. They are hence more susceptible to temperature. This is a significant distinction between BJT and Mosfet. 


Applications of MOSFET and BJT

MOSFET Applications

  • Power Amplifiers: MOSFETs can effectively amplify signals with low distortion and high power output, making them a preferred choice for power amplifiers in audio systems.
  • Switching Power Supplies: In switching power supply, MOSFETs are frequently utilized to efficiently control and transform electrical energy. They permit high-frequency switching, which makes power supply designs for smaller and lighter loads possible.
  • Motor Control: For precise speed and direction control of electric motors, MOSFETs are used in motor control circuits. They are appropriate for high-performance motor control applications due to their quick switching speeds and minimal power dissipation.
  • LED Lighting: To lower and regulate the brightness of LEDs, MOSFETs are utilized in LED lighting applications. They can manage the large currents necessary to drive LEDs and offer effective power management.
  • Solar Power Systems: MOSFETs are used in solar power systems for power conversion and maximum power point tracking (MPPT). They make it possible for batteries or the grid to efficiently transfer power from solar panels.
  • Microprocessors and Memory: MOSFETs are the primary building blocks of memory and microprocessor chips. In computers and other electronic devices, they serve as the fundamental building elements of digital logic circuits, enabling data processing and storage.


BJT Applications

  • Audio Amplifiers: BJTs are frequently employed in audio amplifiers to boost weak audio signals to higher power levels. They are suited for high-fidelity audio applications because they have low distortion and high gain.
  • Radio Frequency (RF) Amplifiers: BJTs are used in radio frequency (RF) amplifiers, which are used in communication systems to amplify radio frequency signals. They provide effective signal amplification in wireless communication systems due to their high gain and wide bandwidth.
  • Switching Circuits: Digital logic circuits and power control applications frequently employ BJTs as switches. They are suited for applications that need for quick switching and strong power handling since they can manage high currents and voltages.
  • Voltage Regulators: To regulate and stabilize voltage levels, voltage regulator circuits use BJTs. Despite changes in input voltage or load conditions, they aid in maintaining a consistent output voltage.
  • Oscillators: Oscillator circuits employ BJTs to produce continuous waves at predetermined frequencies. They are crucial parts of timing circuits, signal generators, and radio transmitters.
  • Automotive Electronics: BJTs are used in engine control units (ECUs), ignition systems, and power management modules in the car industry. In challenging automobile settings, they offer dependable switching and amplification operations.



Transistors are the foundation of contemporary electronics, allowing for the development of strong and portable gadgets that have completely changed our way of life. We examined the differences between MOSFET and BJT transistors in this blog post, in-depth their operational theories, uses, benefits and drawbacks, etc. Transistors will keep playing a critical role in determining our destiny as technology develops. The options are boundless, from exploring novel transistor materials to expanding the number of transistors in CPUs. Our ability to appreciate the wonders of contemporary technology is enhanced by our knowledge of transistor complexity, which also creates opportunities for electrical innovation.



Ella is a skilled embedded systems engineer with experience in PCB design and microcontroller programming. She is committed to following the most recent developments in the field and is constantly seeking for ways to apply them to her work.


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