What is Transistor?
it is a three-terminal semiconductor electronic device. The three-terminal of the transistor are Base, Collector, and emitter. it is widely used in electronics and electrical circuits.it is used as a switch and amplifier in the circuit. when the transistor is used as an amplifier it transfers weak signal from low resistance circuit to high resistance circuit. When it is used as a switch then its gate terminal is used to control the flow of current between collector and emitter.
Construction of Transistor
Construction of transistor can be assumed as two PN junction diode are connected back to back. When two PN Junction diode will connect back to back then it has two PN Junctions. The outer part of the diodes is known as either emitter or collector and the middle part is known as the base. The base is narrow as compared to the emitter and collector. But as compared to the collector, Emitter is narrow.
Transistor Symbol
While representing the transistor on paper, a symbol of the transistor is used that is given below. there are two types of transistors, namely NPN and PNP transistors. When an N-type semiconductor material is sandwiched between two P-type materials then an NPN transistor is formed and When a P-type semiconductor material is sandwiched between two N-type materials then an NPN transistor is formed.
Terminal description of Transistor
The terminal of transistors is used to connect it inside the circuit to provide input and to take the output from the circuit. So it becomes necessary to know about the terminal of the transistor. here we will discuss the terminal of the transistor.
What is Emitter Terminal?
It is the first terminal of the transistor. As its name suggests that it emit a majority charge carrier inside the junction. During the operation of the transistor, the emitter is always forward biased with respect to the base terminal. Due to emitting nature of the majority charge carrier, it is highly doped and its width is wider than the base. In symbol, it is represented by capital letter E.
What is BaseTerminal?
it is the middle part of the transistor and is used to control the flow of electric current between the emitter and collector terminal of the transistor. it is the common terminal of the transistor. its width is narrow as compared to both emitter and terminal. In Symbol it is represented by capital letter B.
What is CollectorTerminal?
It is the left part of the transistor and the last terminal of the transistor. As its name is collector because it collects the majority charge carrier of transistor that is emitted by emitter during the operation of the transistor. its width is wider than the base and emitter. it is always reversed bias. it is represented by the capital letter C.
What is Biasing of transistors?
When all three terminals of the transistor are connected by external voltage then it is known as biasing of transistor. there are two ways to connect a transistor with the external voltage source it means that there are two ways of biasing a transistor :
- Forward Bias
- Reverse Bias
Working of Transistor
As we have discussed above a transistor is used either as an amplifier or switch. Both operations of the transistor are different and also working of the transistor in different modes is different.
Transistor As a Switch
When the transistor is used as a switch then its base terminal is used as ON/OFF by providing an appropriate base voltage. Controlling the flow of current between emitter and collector by providing base voltage is done in both types of BJT either NPN or PNP. The basic Switch connection of the transistor is shown in the given figure below
Transistor As Amplifier
In most DC circuits transistor is used as an amplifier. When the transistor has used an amplifier, its emitter-base terminals are forward biased and Emitter collector terminals are reversed bias. Biasing of the different terminals are the same in both types of BJT whether it is NPN or PNP. The basic Connection of the transistor as an amplifier is given below.
From the circuit diagram, it is clear that a weak signal is provided on the base terminal and the amplified version of the weak signal is taken out between the emitter and collector terminal.