NPN Transistor: What is it? (Symbol & Working Principle)

Hi, readers welcome to the new post. In this post, we will describe the Introduction to NPN Transistor. In the NPN transistor, there is 2 N and one P semiconductor materials are assembled. P is in med and N is at two ends. Generally, the transistor is used in the switching and amplifier process.

It has three main pinouts that are emitter, base, and collector. These components are linked in the circuit where it is used and perform respective functions. here we discuss different parameters related to NPN transistors. So let’s get started

What Is an NPN Transistor?

• The BJT transistor is the main component of electronic circuits and it has two types NPN and PNP.
• NPN is a 3-pin semiconductor layers transistor configured in a combination of P between two N layers.
• Transistors are used to control the current due to the layered design that works as the main component of operation.
• The collector-base junction is reverse-biased. That shows that electron passes is affected through voltage applied.
• But the electrical field removes most of the electrons that cross the emitter-base junction over the collected base junction. IN a result amplify current passing from the emitter to the collector.

NPN transistor symbol

Construction of NPN Transistor

• NPN transistor was created with the use of 3 semiconductor layers one P layer is connected between 2 N layers
• There are 3 pins of this transistor emitter-base and collector.
• Emitter terminals is at the left side of the N layer. Collector connected at right side N layer. The base terminal is Player.
• There are two PN junctions configured in this transistor. ON is the emitter-base configuration and the other PN junction is the collector-base junction or collector junction.

NPN Transistor Circuit

• NPN transistors are used for different circuits and the commonly used configuration is the common emitter configuration used for signal amplification.
• Here emitter is connected to the ground the collector with a positive supply and the base is connected with the input signal supply. Load resistor connected with a collector to control output volts.
• If small input volts are at the base regulates the current flow emitter to a collector as a result input gets amplified.
• Load resistor used at collector terminals and converted amplified curent in voltage signal
• Common emitter design offers high voltage gain and middle-value current gain that work as amplifiers.
• It has low impedance and high input impedance that affect on frequency circuit response.

Operating Mode of Transistor

Three modes of operation transistors are listed here

• Cut-off mode
• Saturation mode
• Active mode
• Transistors operate in three modes that are active, saturation, and cut-off modes. The operating modes of transistors are defined based on the voltage given to the transistor.

Active mode: 

• In-mode transistors work as amplifiers. Base emitter junction if in forward biased state small curent flow from base to emitter. This current control is larger curent in the collector-to-emitter and provides an amplified output signal.

Saturation Mode

• This switch works with the transistor. The base emitter is in a forward-biased state resulting in a high current from collector to base. Transistors work in saturation if the collector current is high and increases in base current not cause an increase in collector current.

Cutt off Mode

• It is off state of the transistor. The base-emitter junction is reverse-biased providing current to move the base to the emitter. Colletor current is small and transistors work like an open circuit.
• The operation mode of the transistor is regulated through varying voltage at terminals. The base-emitter voltage controls the working mode of the transistor, and the collector-emitter voltage measures the magnitude of the output signal in the active mode

 Why n-p-n Transistors Most Used

• The NPN has majority charge carriers as electrons control to NPN transistor that has hole has a majority. Electrons move easily as compared to hols in the crystal lattice. So their mobility is higher and work fastly offering good working.
• The structure of silicon-based transistors is lost cost since larger N-type silicon wafers are used. While production of PNP transistor needs 3 times more surface of the wafer and increased manufacturing cost
• Now negative ground is used as standard and the polarity of NPN transistors design preferred the negative ground.

Features	NPN Transistor	PNP Transistor
Structure	N layer between 2 P-layers	P layers between two N
Current Direction	Collector to Emitter	Emitter to Collector
Majority Carriers	Electrons	Holes
Minority Carriers	Holes	Electrons