Transistor application 

The transistors will be termed as the building blocks of the whole electronics field that many applications are written after transistors. In this article, we are discussing applications of transistors, the discussion includes multiple topics such as applications of a transistor in daily life, BJT transistor application, NPN transistor application, PNP transistor application, Power transistor application, transistor application circuits, transistor uses.


The applications of the transistor are not limited to the single-sided way, because each of the applications is mostly dependent on the types of transistors such as BJT, FET, MOSFET, Darlington transistor, Schokky transistor, multiple emitter transistor, Phototransistor, and Avalanche transistor, etc. 


Application of transistor in daily life


We mentioned earlier transistors are named as the building block of electronics, modern daily life is mostly dependent on electronic systems, and so naturally day to day applications also include transistors.


1.   Transistors have applications in both analog and digital circuits.


2.   Power regulator at the power supply section of electronic devices have,

  • Mobile phone charger
  • AC to DC adaptors 
  • TV power supply section
  • SMPS 
  • Tape recorder


       3.   Integrated circuits build with thousands of transistors.

  • Microcontrollers
  • Microprocessors 
  • Logical blocks


5. The logical operation of the microcontrollers and microprocessors is done with transistors.


6. Amplifier circuits use transistors as the amplification element.


BJT transistor application 


BJT transistor application
BJT transistor application


The bipolar junction transistor has enormous applications in almost every electronic circuit, BJT is a three-terminal device namely collector, emitter, and base, which is in two types NPN transistor and PNP transistor.


The BJT had great applications in switching circuits and amplifier circuits, switching circuits such as smaller devices to large circuits, transistors are known as the electronic switches, normal switches have minimal switching frequency, but transistor as switch works with up to 1000 HZ frequency.


And also BJTs works as an amplifier circuit, the level of amplitude of a signal is increased with the amplifier circuit, this function is done with different circuit connection of transistors such as common emitter, common base, and common collector.


NPN Transistor application 


NPN Transistor application
NPN Transistor application
Here it is clear that the n-type semiconductor is the majority carrier, the application of NPN transistors greater than PNP transistor due to the flowing nature of the n-type electrons higher than p-type holes. The NPN transistor is the BJT transistor type, which is consists of two n-type semiconductors separated with a thin layer of p-type semiconductors.

The NPN BJT transistor is a three-terminal device such as emitter, base, and collector, the connection of supply voltage is always in a way that collector will connect to positive, emitter terminal to negative and base terminal for control ON/OFF state of the transistor, which is depended on voltage.


The NPN transistors have applications in switching devices as small and large circuits, amplifier circuits, higher frequency devices, push-pull complementary transistors amplifier, and logical convertor applications. 


PNP Transistor application


PNP Transistor application
PNP Transistor application


The PNP BJT transistors are completely different from NPN transistors starting from internal structure to the whole working.


In the PNP transistor, we can see two p-type semiconductors is separated with a thin layer of n-type semiconductor, this is the reason why PNP transistors have p-type holes as majority carriers.


A small amount of base current can have the ability to control the large emitter-collector current, because of this the PNP transistor is known as the current-carrying device.


The PNP transistors are also a three-terminal device namely emitter, collector, and base and the symbol indicates that the base current flows outside.


The PNP transistor has applications in the high current application, high switching devices, Power amplifier applications, emergency shutdown devices (high-speed operation), Darlington pair circuits, matching pair circuits, heavy motor to control high current flow, and robotic applications.

Power transistor application


Power transistor application
Power transistor application


Before going to the applications of the power transistor, we need to know a basic idea about power transistors.


The power transistors are not a different device compare to the normal transistor, the basic structure and functionality of the power transistors are the same as the normal transistor, but the power rating or capacity of the power transistors is higher than the normal transistor.


This is the reason why the power transistors are the main component in power electronics applications, the general current rating of the power transistor is higher and voltage must be a constant range.


Every transistor types have its power transistor type, even it is BJT, the combination of PNP-NPN complementary transistor are works as a power amplifier, this is also a power transistor type, high frequency switching application, high current power supply applications, high current motor controlling applications, IGBT at inverter applications, Field-effect transistor (FET) on current controlling applications, POWER MOSFET at vehicular automation and automotive systems applications.


Transistor application circuits 


 1.   Common emitter circuit


Common emitter circuit
Common emitter circuit


The common emitter configuration is a commonly used transistor network, the circuit connection of this configuration is like, the transistor base terminal acts as the input of the circuit and transistor collector serves as the output of the circuit, and the transistor emitter is taken as a common connection for both base and collector.

This is the reason why the connection is a common emitter configuration.


Important points of common emitter circuit

  • Common emitters provide a much-improved voltage gain with an average current gain.
  • Common emitter have moderate input and output impedance 
  • The normal working of the circuit will be like, they invert the input signal, and in other words, we have a 180-degree phase shift across the circuit output.
  • Common emitter circuits need few components to build the circuit.


Applications of common emitter circuit 


1.   Audio amplifier circuit

2.   Low-frequency voltage amplifier

3.   Basic switching circuit for logic circuits

4.   Radio 

2.   Common collector circuit 

Common collector circuit
Common collector circuit


The common-collector circuit has applications in high current circuits, the transistor common collector circuit connections are like, and the input of the circuit taken between emitter-base terminals and the output of the circuit are collector-emitter.


Important points of common collector configuration

  • The common collector configuration has high input impedance and low output impedance.
  • The voltage gain for the circuit is less than and they had a larger current gain.
  • The signal from this circuit has input and output signals that are in-phase.


Applications of the common collector circuit


1.   Non-inverting amplifier circuit 

2.   These circuits are used as impedance matching device

3.   Used at the digital circuit at logical network

4.   Used at switching circuits

5.   Used on high current gain circuit applications 

 3.   Common base circuit


Common base circuit
Common base circuit


In the circuit, the transistor base terminal is taken as common for both input and output of the signal. 


The input signal is applied between transistor base-emitter terminals and corresponding to this output is taken between transistor base-collector terminals with the base terminal is grounded.

Important points of the common base configuration 

  • For this common base configuration, the current gain is generally equal or less than the unity.
  • The voltage gain of this circuit is high, due to this reason construction of the circuits is difficult.
  • They had high output impedance and low input impedance.
  • The input and output signals are in-phase in this circuit.

 Applications of the common base circuit 


1.   It is used as a non-inverting amplifier.

2.   Used as pre-amp at moving coil microphones.

3.   Used at UHF and VHF, RF amplifier.

4.   Used at low-frequency circuit application.

5.   Used as the current buffer circuit.


 4.   Common emitter transistor amplifier circuit 

Common emitter transistor amplifier circuit
Common emitter transistor amplifier circuit


The common emitter amplifier circuits are basic single-stage amplifiers, it will work as voltage amplifiers.


As same as common emitter configuration, the input is taken base terminal of the transistor, the output may take from collector terminal, the emitter is common for input and output terminal.


Circuit explanation of common emitter transistor amplifier circuit 


The circuit shown below is the amplifier circuit, at input R1-R2 resistor network to form a voltage divider, used to provide biasing voltage to the transistor.


The RL resistor is used at the output is the load resistor, RE resistor is for thermal stability of the whole circuit.


Then the C1 capacitor is the input capacitor for separate AC signal from the DC biasing voltage known as a coupling capacitor.


5.   Emitter follower transistor circuit

Emitter follower transistor circuit
Emitter follower transistor circuit


The construction details of transistor emitter follower circuits are much similar to the amplifier circuit. 

The output is taken from the transistor emitter terminal, instead of the collector terminal is the specialty of the emitter follower circuit.

The input is provided in between base-emitter terminals.

Important points of emitter follower circuit 

  • The circuit has no voltage gain, but high current gain and power gain.
  • High input impedance and low output impedance.
  • Input and output signals are in-phase.
  • It has an idle current for the impedance matching function.
  • The emitter follower circuit is also known as the common collector circuit.

Applications of emitter follower at some circuits

1.   Adjustable Zener diode 

These circuits are mainly used in cell phone charger circuit applications.

1.   Simple motor speed controller

The motors will be connected across the transistor emitter terminal for controlling the speed of the motor.


 6.   Two transistor amplifier circuit 

Two transistor amplifier circuit
Two transistor amplifier circuit


The main application of the transistors is the amplifier circuit, normal single-stage amplifiers proved much lower power output, two-transistor amplifiers or two-stage amplifiers consist of NPN and PNP transistors are willing to provide high power output.


One of the specialties of this circuit is, the circuit components in the amplifier is few and the transistors used at the circuit are complementary transistors.


Important points of two transistor amplifier circuit

  • The amplifier circuit provides sufficient gain or output impedance matching 
  • The circuit provides you a higher level of input-output isolation
  • The circuit has a higher gain or higher bandwidth 


Disadvantages of two transistor amplifier circuit 

  • The circuit has low power output for effective output load.
  • They had a noisy output signal when the circuit become aged.
  • The circuit had poor power transferability
  • Poor impedance matching capability
  • The circuit is bulkier in size
  • The circuit also needs heavy power supply circuits.

7.   Transistor as a switch


Transistor as a switch
Transistor as a switch


The transistor works like a normal switch at circuits, but the frequency of the switching needs to vary at applications by modifying the circuit, high-speed switching up to 1000 or 2000 HZ is the capability of the transistor switching circuit.
We know transistors are called the electronic switch, on the lights of that usage, switching applications using transistors are enormous at electronic circuits.

Generally, transistor works in 4 regions of operations, namely active state, cutoff state and saturation state, each of the circuits working will be based on the transistor in these operating regions.

The transistor operates in saturation and cutoff regions, for the working of switching circuits.

The circuit shown above is the transistor ON/OFF switching for LEDs, RB transistor base resistor setting up a voltage for the transistor to start working, which is 0.7v, connected between emitter-base terminals.

At the same time, the collector-emitter junction flows no voltage.

In this condition, the transistor operates as the switch and LED glow.

In the same way, no voltage is applied at the input terminal, the transistor function in the cutoff region, and functions as an open circuit.

The transistor switching operation have application in more circuits, bigger to smaller circuit applications


1.   Inverter switching

2.   SMPS switching 

3.   Multi-vibrator switching


8.   Relay driving circuit using transistor 



Relay driving circuit using transistor
Relay driving circuit using transistor

The relays are one of the important components in electronics, they are termed as the output device which is available in different shapes, size and they had enormous applications in electronics.

Typically relays are used to control (ON/OFF), a high-power device using an electronic setup.


Operation of relay driving circuit using transistor 


The circuit above is the relay driver transistor circuit, consist of the relay with flyback diode and transistor with base resistor RB.

The transistor base driver voltage to the transistor is the main source for controlling the relay operation, so they need to be much calculated and properly selected.

The RB base resistor is based on the current across the collector-emitter terminals of the transistor or also called the relay coil current.


Applications of a relay driver circuit using transistor 


This is a relay driver circuit using transistor, application of this particular circuit mainly at was the interaction happened between AC and DC at the same circuit.


1.   AC to DC converter circuit

2.   Inverter circuit 

 And circuit applications also at high current circuits

1.   Motor controlling devices

2.   Industrial automation systems 

3.   PLC systems

4.   Signaling systems at railway networks

5.   Distribution networks 


Conclusion for transistor application 


We know the world without transistors is called no development in electronics and technology, before the invention of transistors, the world starts working differently, the involvement of transistor applications is explained in this post not over.

The transistor works as an energy valve, using the input trigger to control the output signal, if it is a switching circuit using a transistor or amplifier circuit using a transistor, the transistor works in the almost same way, the only difference is the transistor region of operation.

When we moving on to the application level of the transistor, the working operation of the transistor circuit application is almost the same, but over the days, for the circuit’s different transistors are available for different circuits and also for different energy levels.


Transistor as a application
Transistor as a application


The BJT and MOSFET are two types of transistors, but design for different circuit applications, comparing both BJTs and MOSFETs, we can spot a higher amount of protection systems and a higher level of power delivering at MOSFETs.

For example bipolar junction transistor is used for amplification, switching and moderate energy level circuits, but the case is the same at the field-effect transistor, they are a current controlling transistor, used at extra high current applications, MOSFETs are another type of transistor, which is fastest switching component, specifically for inverter, UPS and SMPS circuit applications.


We can conclude this post as transistors have a great plot at any level of electronic development, if it is analog or digital, or if it is a small sensor or automation system, we can spot a transistor on the inner component.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *