Different Applications of Transistor and Mosfet

Today, I'm going to give you an overview of the Different Applications of Transistor and Mosfet. This blog is the continuous blog of the series of Transistors so if you wish to read about any other transistors then you may click HERE

Bipolar Junction Transistor

Bipolar Junction Transistor, BJT, Power transistor, BJT symbol, BJT vi characteristics, Power BJT, PNP, NPN
A BJT is a bipolar junction transistor, which is capable of handling two polarities (holes and electrons), it can be used as a switch or as an amplifier and is also known as a current-controlled device.


Transistors are used as a switch in a broad range of applications, including connecting high-current or high-voltage devices such as motors, relays, or lights to low-voltage digital ICs or logic gates such as AND gates or OR gates.

Alternatively, the speed of a load, such as a DC motor, may need to be regulated through a sequence of pulses (Pulse Width Modulation). Transistor switches will allow achieving this more quickly and easily than mechanical switches.

Transistor as a Switch in Digital Logic circuit:

 Digital Logic Transistor Switch, npn  Digital Logic Transistor Switch, pnp  Digital Logic Transistor Switch, transistors in digital circuit, transistor aplications We may also use PNP and NPN transistors as switch; the difference is that the load in PNP is connected to ground (0v) but not in NPN, and the PNP transistor switches power to it. To turn the PNP transistor on as a switch, connect the Base terminal to ground or zero volts (LOW), as shown.

The distinction between PNP and NPN is that a PNP transistor switches power (source current) instead of switching ground like an NPN transistor (sinking current).



 Darlington Transistor Pair based Rain Alarm

 Darlington Transistor Pair based Rain Alarm, Transistors applications, darlington pair applications, darlington pain as a switch


The rain alarm circuit schematic using a Darlington transistor pair (BC547 transistor) is shown. 
This circuit is designed in the form of a normal Darlington transistor pair. These transistors are primarily utilized to boost the capacity of current amplification. When water or raindrops fall on the sensor, the base of the transistor is supplied with the current which further gets supplied to Buzzer and causes the alarm to sound. 

Transistor as an Amplifier

Transistor as an Amplifier, TIP31C as an apmplifier, tip31C, transistor applications

A transistor functions as an amplifier by amplifying a weak signal. When a DC bias voltage is provided to the emitter-base junction, it remains forward biased. This forward bias is maintained irrespective of the signal's polarity.

Because of the low resistance in the input circuit, every minor change in the input signal results in a large change in the output. The input signal's emitter current goes to the collector current, which then flows through the load resistor RL, causing a high voltage drop across it. As a result, a small input value results in a big output voltage, indicating that the transistor functions as an amplifier.


Some Common General Purpose Transistors:

Transistor BC638 BC488 2N4400 BC490 2N3053 2N4402


Some common Power Transistors:

TIP31C – NPN Power Transistor TIP32C - PNP Power Transistor
TIP127 - Darlington NPN Transistor TIP122 - Darlington PNP Transistor
TIP110-112 Complementary Silicon Power Darlington Transistor TIP115-117 Complementary Silicon Power Darlington Transistor
BJE243 Silicon Power Plastic Transistor BJE253 Silicon Power Plastic Transistor
TIP41TIP41ATIP41BTIP41CComplementary Silicon Plastic Power Transistor TIP42TIP42ATIP42BTIP42CComplementary Silicon Plastic Power Transistor
BD135BD137BD139Plastic medium power Silicon Transistor BD136BD138BD140 Plastic medium power Silicon Transistor
TTC5200 Silicon Triple Diffused Transistor TTA1943 Silicon Triple Diffused Transistor





MOSFET , N channel MOSFET, P channel MOSFET, MOSFET symbol

MOSFET stands for Metal Oxide Field Effect Transistor, MOSFET is a three-terminal device with source, base, and drain terminals. It is a sub-classification of the FET transistor. 

VI characteristics of a MOSFET, MOSFET, N channel, P channel

The MOSFET is Classified into two types based on the type of operations, namely Enhancement mode MOSFET (E-MOSFET) and Depletion mode MOSFET (D-MOSFET)



MOSFET as a Motor Controller

MOSFET as a Motor Controller, MOSFET application


The two MOSFETs are wired together to form a bidirectional switch from a dual supply, with the motor linked between the common drain connection and the ground reference. When the input is set to LOW, the P-channel MOSFET is turned ON because its gate-source junction is negatively biassed, causing the motor to revolve in just one direction. The motor is driven only by the positive +VDD supply rail.

When the input is HIGH, the P-channel device turns OFF, but the N-channel device turns ON because its gate-source junction is positively biassed. Because the motor's terminal voltage has been inverted as it is now fed by the negative -VDD supply rail, it now rotates in the other direction.

MOSFET Motor Control Table

MOSFET 1 MOSFET 2 Motor Function
OFF OFF Motor Stopped (OFF)
ON OFF Motor Rotates Forward
OFF ON Motor Rotates Reverse

 MOSFET used in voltage regulator circuits

 MOSFET used in voltage regulator circuits, MOSFET applications, MOSFET

In voltage regulator circuits, depletion-type MOSFETs with source-follower connections are employed. The illustration depicts a linear voltage regulator circuit. VL follows the gate voltage(VG), minus the gate-to-source voltage(VGS), in this regulating circuit. Furthermore, when the drain current increases(Id), the gate-source voltage(VGS) also increases. So that the gate voltage remains constant, the source voltage decreases as the load current(IL) increases.

MOSFET as a Chopper

MOSFET as a Chopper, MOSFET application

The figure shows how the switching behavior of MOSFETs may be used to construct chopper circuits. By biassing the MOSFET with a square voltage waveform between its gate and source terminals, the DC voltage(VDC), is turned into an AC(VAC) voltage with the same amplitude level. As a result, the MOSFETs alternate between operating in the cut-off and saturation areas.

Power MOSFET in Inverters
Power MOSFET in Inverters, Mosfet application, MOSFET

With a rectifier and filter, this inverter can deliver high-voltage AC or DC up to several hundred volts. T1's secondary and primary windings, a 12.6 to 440 V power transformer. Q1 and Q2 can be any type of power FET. 

Some Common MOSFET’S:

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