Transistors are the major components in electronics. It is used to amplify and switch electronic signal. All transistors have minimum 3 leads to connect to an external circuit.A voltage or current applied to one pair of transistor's terminals control the current flow through another pair of terminals.The controlled power can be much more than controlling signal.This makes transistor as a more valuable one.
Transistor is considered as the greatest inventions of the twentieth century.
We can divide transistor in to two categories.
FET and BJT
The bipolar junction transistor, or BJT, was the most commonly used transistor in the 1960s and 70s. Even after MOSFETs became widely available, the BJT remained the transistor of choice for many analog circuits such as simple amplifiers because of their greater linearity and ease of manufacture. Desirable properties of MOSFETs,such as their utility in low power devices, usually in the CMOS configuration, allowed them to capture nearly all market share for digital circuits; more recently MOSFETs have captured most analog and power applications as well, including modern clocked analog circuits, voltage regulators, amplifiers, power transmitters, motor drivers,
etc.
Basics of BJT
You can get more information about transistors from texts. So just try to refer a text or a web page about transistor.
Transistor switching
Now i like to simplify a BJT operation to understand its practical application as a switch.
We know that a transistor have three leads.They are
1) emitter
2) base
3) collector
BJT is also again divided in to two type, NPN and PNP transistor.
Just consider a NPN transistor. A small current is applied to the base of transistor, then the current flow from the collector to emitter was controlled by that base current.
You have any problem?..
Leave all...
Already we have more practical experience in traffic jams. So just consider a one way in a city. I more like calicut because there is at least 10 traffic jams and other road problems in each one hour...
You can imagine, that is your right.
Hurry....
Now a traffic signal is placed at the center of way.
Very nice... RED, YELLOW, GREEN lights.
Now you can see , some person try to break all laws. So don't care about them.
Really sorry, i remember some persons like you. So just leave it.
Return to our traffic signals...
When RED light comes, all vehicle are waiting.
When GREEN light comes, zo zo..........zo..
Leave YELLOW, he is a waste for us.
Hear traffic light control the flow of vehicles from one end to another.
Now we replace all names with electronics. The starting of one way is called emitter in NPN transistor and collector in PNP transistor. The end is called collector in NPN transistor and emitter in PNP transistor.
Not try to confuse, just try only one type, either NPN or PNP.
What is the new name of traffic light?... No doubt, it is the base of transistor.
Now we try to understand the operation of transistor as a switch. The base current control the flow of current from emitter to collector in NPN transistor. Also base current control the flow of current from collector to emitter in PNP transistor.
According to base current , the collector current and emitter current is increasing or decreasing.
Now try to explain the switching action of transistor in a paper with your own theory. Always remember my traffic light.
Leave all old theory.. Create new one.
Try it...