Working of NPN Transistor
Forward bias should be used at the base-emitter junction, and reverse bias should be used at the collector base intersection. As a result, the negative terminal of the VBE is linked to the N-terminal of the emitter-base intersection, and the positive terminal of the battery is linked to the P-terminal of the VBE. The N-terminal is connected to the VCB’s positive terminal to invert the authority base intersection, while the P-terminal is connected to the battery VCE’s negative terminal. As a result, the gatherer base intersection will have a wide exhaustion layer and the emitter base intersection will have a limited consumption layer.
The electrons in the N-area will repel from the battery’s negative terminal and move toward the base region when forward bias is applied to the emitter-base junction. When compared to the area of the emitter and collector, the base area is very small. Additionally, the base’s doping force is greatly diminished. As a result, there are fewer holes in it.
A few electrons and holes will recombine due to the absence of many holes in the base region. Various electrons that have not yet recombined will move toward the gatherer district. This will include the circuit’s current. Because of its enormous size, the gatherer can dissipate heat and gather additional charge transporters. Since electrons are the primary charge transporters in the NPN transistor, the current is caused by electrons. The emitter current in an NPN semiconductor is equivalent to the amount of base and gatherer current. Numerically it tends to be composed as:
IE = IB + IC
In NPN transistor , in the common emitter configuration, the emitter is doped heavily compared to that of collector and current flows from base to emitter , as NPN transistor is used in CE configuration as an amplifier so we will discuss it in detail:
Common Emitter Configuration
The base is the input terminal in a common emitter configuration, the collector is the output terminal, and the emitter is the common input and output terminal. This indicates that the collector terminal and the common emitter terminal are referred to as output terminals, while the base terminal and the common emitter terminal are referred to as input terminals.
In like manner producer design, the producer terminal is grounded so the normal producer setup is otherwise called grounded producer arrangement. Common emitter configuration, common emitter amplifier, and CE amplifier are also sometimes used interchangeably. The most common transistor configuration is the common emitter (CE) configuration. When a significant current gain is required, common emitter (CE) amplifiers are utilized. The base and emitter terminals receive the input signal, while the collector and emitter terminals receive the output signal. The term “common emitter configuration” refers to the fact that a transistor’s emitter terminal serves as both the input and output terminal.
VBE is the supply voltage between the base and the emitter, and VCE is the supply voltage between the collector and the emitter. IB stands for input current, also known as base current, and IC stands for output current, also known as collector current, in a configuration known as common emitter (CE). The input and output impedance levels of the common emitter amplifier are moderate.
Therefore, the common emitter amplifier has a voltage gain and current gain that are medium. However, the gain in power is substantial. We require two sets of characteristics—input characteristics and output characteristics—to fully describe the behavior of a transistor with CE configuration.
α and β Relationship in a NPN Transistor
DC Current Gain=[Tex]\frac{Output Current}{Input Current}[/Tex]=[Tex]\frac{I_C}{I_B}[/Tex]
using KCL
[Tex]I_E=I_B+IC [/Tex]
[Tex]\alpha=\frac{I_C}{I_E}[/Tex]
so,
[Tex]\beta[/Tex] can be calculate as
[Tex]\beta=\frac{I_C}{I_B}=\frac{I_C}{I_E(1-\alpha)}=\frac{\alpha}{1-\alpha}[/Tex]
Input Characteristics of NPN Transistor: Input characteristics refer to the curve between base current and base-emitter voltage for a particular collector-emitter voltage value.
Output Characteristics of NPN Transistor: In below figure shows the output characteristics of an NPN transistor. The curves show the connection between the collector current (IC) and the collector-emitter voltage (VCE) with the differing base current (IB). We realize that the semiconductor is ‘ON’ just when essentially a modest quantity of current and a limited quantity of voltage is applied at its base terminal compared with a producer in any case the semiconductor is in an ‘OFF’ state.
The collector current (IC) is for the most part impacted by the collector voltage (VCE) at 1.0V level however this IC value isn’t exceptionally impacted over this value. As of now, we realize that the emitter current is the amount of base and collector current. for example IE =IC+ IB. The ongoing coursing through the resistive load (RL) is equivalent to the authority current of the semiconductor. The condition for the authority current is given by,
IC= (VCC-VCE)/RL
The straight line demonstrates the Dynamic load line which is interfacing the focuses A (where VCE = 0) and B (where IC = 0). The region along this heap line addresses the ‘active area’ of the transistor. The common emitter design attributes bends are utilized to ascertain the gatherer current when the collector voltage and base current are given. The heap line is utilized to decide the Q-point in the diagram. The incline of the heap line is equivalent to the proportional of the heap opposition. i.e. -1/RL.
NPN Transistor
An NPN Transistor is a Negative-Positive-Negative transistor that has a significant and varied impact on electronic circuits. The NPN transistor is made up of three semiconductor layers that are arranged in a particular way. One of the layers is of the negative (N) type and is sandwiched between two of the positive (P) types.
Its name is derived from this distinctive arrangement: NPN. Electrons flow from the N-type region through the P-type region when a voltage is applied across the transistor’s terminals, resulting in controlled conductivity and allowing the transistor to act as an amplifier or switch.
Table of Content
- NPN Transistor
- Construction
- Working
- Applications
- Advantages
- Disadvantages