Difference Between BJT and MOSFET

In day to day life, electricity plays an important role and so does the current. Current is the flow of charged particles like electrons or ions, through conductive materials such as metal wires.


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The flow of current is determined in the circuit which includes wire, switch, battery, and an electronic gadget (mostly bulb), this is the most basic circuit, one can show for a basic explanation.

Transistors have three terminals (emitter, base and collector) which enables it to connect to an external circuit. They are active components of integrated circuits. 

There are two types of transistors mainly; BJT abbreviated for Bipolar junction transistor and FET abbreviated for Field-effect transistor.

Key Takeaways

  1. BJT (Bipolar Junction Transistor) is a type of transistor that relies on electrons and holes as charge carriers and operates through the control of the base current.
  2. MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is another type of transistor that controls current flow through a semiconductor channel by applying a voltage to the gate terminal.
  3. Key differences between BJT and MOSFET include their charge carriers, operating principles, voltage requirements, and switching speeds, with MOSFETs generally offering higher input impedance and faster switching times.


The difference between BJT and MOSFET is that the BJT is used as a current control device whereas MOSFET is used as a voltage control device. Both of them are considered good options for amplification yet they have differences in their workings.


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Comparison Table

Parameters of ComparisonBJTMOSFET
Hardware constructionEmitter, base, and collectorSorce, gain and drain
Preferred for applicantsLow current applicationsHigh power, current control applications
Input impedanceLowHigh
Temperature coefficientNegative temperature coefficientPositive temperature coefficient
DeviceCurrent controlling devicesVoltage controlling devices


What is BJT?

BJT is an abbreviation of Bipolar junction transistors, it is a type of transistors which uses charged electrons and electron holes as well. It is a current-driven device.

BJT is used as an amplifier, oscillator or even as a switch in several things. It has three terminals or pins mainly; base, collector and emitter. The collector or emitter output is the function of current in the base.

Operation of BJT transistor is driven by the current in the base. BJT is bipolar hence there are two junctions named as ‘P’ and ‘ N’. There are two types of BJT; PNP transistors and NPN transistors.

Some of these applications of BJT are; audio amplifiers in stereo systems, power control circuits, AC inverters, power amplifiers, switch-mode power supply, AC motor speed controller, relay and drivers, etc..

BJT transistor consists of mainly four layers; the first layer is the emitter layer (n+) which is heavily doped, the second layer is the base layer (p) which is moderately doped, third layer collector drift region (n-) which is lightly doped, and the fourth layer collector region (n+) which is highly doped.

BJT is preferred for low current applications, as it has low switching frequency and has a negative temperature coefficient.


What is MOSFET?

It is also known as metal oxide-silicon-transistors, it can be classified as a type of transistor which has insulated-gate field-effect transistors which are further fabricated by the controlled oxidation of semiconductor mostly with silicon and it is unipolar.

MOSFET is used for amplifying or switching the voltage within the circuit. The field produced by the voltage at the gate allows the flow of current between the source and the drain.

MOSFET working depends upon the MOS capacitor which is the semiconductor surface between the source and the drain. their infinite input impedance allows the amplifier to catch almost all signals.

MOSFETs are available in two basic forms; depletion type in which the transistor requires the gate-source voltage to switch the device off.

Applications of MOSFET includes; radio-controlled applications (such as boats, drones, or helicopters), controlling the auto intensity of street lights, motor torque-speed control, industrial control environment, robotics, pairing with microcontrollers to establish systems that control lights, etc.

MOSFET is suitable for high power, current control applications and even for analogue and digital circuits. Its output is controlled by controlling the gate voltage. It has a positive temperature coefficient.


Main Differences Between BJT and MOSFET

  1. BJT is used for current control devices whereas MOSFET is used for voltage control devices.
  2. The input impedance of BJT is low on the other hand input impedance of MOSFET is high.

  1. ttps://ieeexplore.ieee.org/abstract/document/8249838/
  2. https://ieeexplore.ieee.org/abstract/document/1486756/
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