What is transistor | transistor definition

 

What is transistor?

The transistor is an electronics switching device or component. it is the semiconductor electronics component, this is made by semiconductor material, such as Silicon, Germanium, Gallium Arsenide, etc.

It use for switching or amplifying to electrical signals and current or power. It has only these two main functions, which are switching and amplification, it has no other function.

The transistor gives most revolution to modern electronics or industries also innovations. Because the Cell phones, Computers, Laptops are based on micro processor and processor based on the transistor, it shows that the all digital technology spread with help of transistor.
The function of a transistor is very similar to a mechanical switch, but we cannot switch fastly by mechanical switch, but transistor can very fatly control to switching.

Any transistor has three pins or terminals.

      1-    Input pin

      2-   Output pin

      3-   Signal pin

But we have transistors of different values, so any transistor has the same pins, but it pins placed in different places, it depends on the design of the circuit.

Placement change stands for, transistor pin such as Input - Output - Signal, or Signal - Input - Output, or Output - Input - Signal and Input – Signal Output, etc.

Working of Transistor & How to use transistor

1- Switching

Switching means ON or OFF to any device, it can turn ON or OFF current a million times a second. It we use where we want high frequency or switching, this means that where we need to turn ON or OFF any device or current many times, so we use a transistor.

Example of switching

Suppose:-

We have a 3v of LED and a battery of 3v, which we want turn ON or OFF by electrical signal, so we will use a transistor, and connect positive wire of LED to battery's positive, while negative wire of battery connect to Emitter of transistor and negative wire Of LED connect to Collector of transistor, so LED will not glow, until give positive signal of battery to Base of transistor, when battery's positive signal connected to transistor's Base, after circuit will complete and glow LED.

You can understand easily by watch this figure,

In this diagram transistor used as a switching 

 2-Amplification

The amplification means convert low signals to high signals, it mostly used in Radio, Telecommunication, and Speaker circuits and etc.
Another, to convert low signals into high signals means that we can control high voltage devices or equipment with the help of transistors through low voltage.

Example of Low Signal to High Signal or Amplify.
This is mostly used in speaker's circuit; because we need audio volume convert to high volume, while audio signals have very low.

Suppose:-
We have a 5v of Bulb and a battery of 5v, which bulb we want ON or OFF by 1.5 signal, so we will use a transistor, and connect positive wire of LED to 5v battery's positive, while negative wire of battery connect to Emitter of transistor and LED negative wire connect to Collector, now use another battery of 1.5v use for signal provide to transistor's Base, but which battery we use for signal, it also has negative and positive wire, positive wire used for signal to Base, but negative wire most be connect to transistor's emitter, so Bulb will not glow, until give positive signal of battery to Base of transistor, when battery's positive signal connected to transistor's Base, after circuit will complete and glow LED.
This example learns it that we low signal converted to high signal, because we control 5v Bulb by 1.5v.

Like same this, in speaker's circuit, where we connected Bulb in above example, there will connect a speaker and audio (Mic) signal connect will instead of 1.5 batteries.

Note:- If we not connect other battery's negative to Emitter so transistor will not properly work.
You can understand better by watch this diagram,

In this diagram transistor used as a amplification.

Types of Transistor

There are two types of transistor.

·              BJT Bipolar junction transistor   

·              FET Field Effect transistor

1- BJT use for low current and it’s used in low power circuits, it is the current controlled transistor, and that is, it can operate by current signal.

The BJT transistor three pins name known by Emitter, Collector, Base.

Input = Emitter

Signal = Base

Output = Collector

Also BJT has two types

·                PNP

·               NPN

There is no big different it has only polarity change.

 In PNP type transistor, Emitter pin required Positive voltage, and Base required negative signal, and Collector will give positive voltage or current.

In NPN type transistor, Emitters pin required negative, and Base required Positive signal, and Collector will give negative current.

Its names clearly show that PNP means Positive - negative - positive and vice versa.

2- FET use for high current or high voltage, it is the voltage controlled transistor, that is, it can operate by voltage signal.

The FET transistor three pins name known by Gate, Drain, Source.

Input = Source

Signal = Gate

Output = Drain

The FET has more two types

1- Junction FET

2- Mosfet

1- The Junction FET operate only in depletion mode and it used for low noise.

Also Junction FET has two types.

1- P channel

2- N channel

The Mosfet has two modes

1- Depletion Mode

2- Enhance Mode

The Depletion mode is same work but it is reverse, when give signal to its gate then it not complete circuit, means when its gate signal remain "0" then it work like closed circuit, when gives voltage signal to gate then it work like open circuit.

2- Enhance mode has not any changing, just to separate the upper mode, the mosfet is divided into two parts.

Again Mosfet has two types in both mode.

1- P channel
2- N channel

There is no big different it has only polarity change.

How to identify Emitter, Collector, Base pins of transistor?

This discussed above that any transistor has three pins, but it placed on different location so how to check emitter, collector or base pins by multimeter.

Step  1

Select the diode range in your multimeter, and connect the meter's probe to each pin of the transistor alternately.

Example:-

Connect the multimeter red probe to one of the transistor pins and the black probe to the other second pin, If the meter shows a reading, leave the red probe in one place and connect the black probe to the third pin of the transistor, If meter shows a reading, it means that the pin with the red probe is the base pin of the transistor, and this means it is the NPN transistor, because the red probe is placed on that pin, and the reading has coming on both pin.

if transistor will be PNP so wire be vice versa, means if black prob of meter connect to Base so meter will show reading to other two pins.

We have identified the base pin.

NOW

Step 2

Connect the first probe of the meter to the base pin, and connect the second probe to the second pin of the transistor, and remember the meter reading, now pick up the probe and connect to the third pin and remember the meter reading again, now compare the two values, The which value is higher than the second value, the higher value is the emitter and the second is the pin collector which has a lower value.