[Exact] Function of Transistor explained with examples

The transistor is one of the most useful and simple electronic components which changed the whole world of electronics. Almost all electronic circuits are used transistors. Integrated circuits or ICs also not possible to make without transistor. In this article, we are going to discuss the main function of the transistor. A transistor is an active device having a minimum of three terminals. There are mainly two types of transistors are mostly used- BJT or Bipolar Junction Transistor, FET, or Field Effect Transistor.

BJT has three terminals named as Collector, Base, Emitter. FET has three terminals named as Source, Gate, and Drain. Both of them are used for different purposes but the function of them almost the same.

Transistor Function

Don't confuse with the function provided by a transistor and the applications of the transistor because a transistor can provide only two functions. Only those two functions we used for different purposes and different applications. The two functions provided by a transistor are,

1. Switching

2. Amplifying

So the two functions provided by transistors are switching of electronic signals and amplifying electronic signals.

Now let's go to understand those two functions with examples.

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Transistor as a Switch

Generally, in digital electronic circuits transistor is used as an electrically operated solid state switch. Transistor is used in both high power and low power switching applications. Using a low power signal we can control or switch the high power signal by using a transistor.

Here you can see the circuit diagram in the below figure where a transistor is used as a switch.

Here, you can see a LED is connected with the DC supply in series with a Bipolar Junction Transistor(BJT) through the Collector(C) and Emitter(E) terminals. In normal conditions, the transistor acts as an open switch so it does not allow the flow of current hence the LED will not glow.

To operate the transistor as a closed switched we have to give a voltage across the base terminal of the transistor. So, here in the above figure, you can see an LDR(Light Dependent Resistor) is connected with the base terminal. So when light is applied on the LDR its resistance will decrease and it allows the flow of current through it. As here a voltage will be applied across the base terminal, the base terminal will consume some current.

Once the voltage is applied across the base terminal, the transistor will act as a closed switch and it allows the flow of current through it, so the LED will be glow.

As the transistor is a solid-state device, no power loss occurs during switching action, and it provides also a very fast switching facility.

BJT is a current controlled device whereas FET is a voltage controlled device. Remember that, mostly Field Effect Transistors(FET) is used for the switching of the electronic or electrical signals, especially MOSFET(Metal Oxide Semiconductor Field Effect Transistor) because they provide very fast switching facility and very low electrical power loss.

Example: Most useful digital logic gates are made of transistors where they act as an electronic switch.

Read Also: Transistor applications explained with examples

Transistor as an Amplifier

Another function of a Transistor is amplifying electronic signals. There are huge applications of transistors as amplifiers in electrical and electronics engineering. All smaller to bigger amplifier circuits use transistors to amplifying the electronic signal.

Here you can see a simple circuit diagram amplifier circuit using transistor,

When we applied a weak electronic signal as an input of the transistor it produces a stronger signal as an output with the help of external reference voltage or biasing voltage. Here in the above figure, you can see the external reference voltage denoted by Vcc.

So, a transistor does not increase the magnitude or power of the input weak signal, it produces a new signal as an output which exactly the same as the input signal, just the difference is, its magnitude is high. Remember that, transistor not able to amplify any electronic signal until we give an external power supply(DC supply) as a reference voltage.

Remember that, mostly Bipolar Junction Transistors(BJT) are uses for the amplifying of electronic signals because they provide higher gain, low noise distortion, etc.

Example: In amplifier circuits, transmitter, receiver circuits transistors are uses for amplifying purposes.

So, the conclusion is, a transistor can provide only two functions, one is switching and another one is amplifying.

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