Introduction to 2n4401

Introduction to 2n4401

• 2n4401 is an NPN bipolar junction transistor which is used for general purpose amplification and switching purpose.
• It is called bipolar junction transistor because conduction is carried out by both charge carriers i.e electrons and holes, but majority charge carriers will be electrons.
• It mainly consists of three terminals called emitter, base, and collector.
• Small current present at the base side is used to control the large current at the emitter and conductor side.

• P layer of this transistor represents the base terminals while other two N layers represent emitter and collector respectively. Base is positive with respect to emitter.
• 2n4401 is actually a current control device where small current at the base side is used to control the large current at the emitter and collector side.
• When a positive voltage is applied at the base side, it gets biased and allows the current to flow from emitter to collector.
• The emitter emits the electrons which are then collected by the collector and base controls the number of electrons.
• A transistor is a combination of diodes joined back to back.

2n4401 Pinout

• Base side of this transistor is lightly doped while emitter side is heavily doped.
• When small current controls the large current at the emitter and collector, this process is used for amplification purpose.

Circuit Diagram of 2n4401

• The voltage at the collector side is more than the voltage at the base side.
• This transistor comes with three main configurations i.e common base configuration, common emitter configuration, and common collector configuration.
• Common emitter configuration is mainly used for amplification purpose because it exhibits the required voltage and power gain for amplification purpose.
• This configuration helps in increasing the input signal by 20dB which is nearly 100 times more than the input signal.
• Emitter current is the combination of base and collector current.
• Collector and emitter can be differentiated by their size and doping concentration. The emitter is highly doped while the collector is lightly doped.
• The forward current gain of the transistor can be denoted by beta ß which is a ratio between collector current and base current. This beta is actually an amplification factor which is a measure of current being amplified. Beta value ranges between 20 to 1000 but its standard value is 200. Beta is a ratio of two current so it has no unit.
• The current gain of this transistor is represented by alpha a which is a ratio between collector current and emitter current. Alpha value ranges between 0.95 to 0.99 and most of the times its value is considered as a unity.

Absolute Maximum Ratings of 2n4401

• Collector-Emitter and Collector-Base voltages are 40 and 60 V respectively.
• If stresses are exceeded above these absolute maximum ratings, they can damage the device.
• Similarly, if stresses are applied for the extended period of time, they can affect the device reliability.

Difference between NPN and PNP transistors

• The main difference between NPN and PNP transistor is the availability of charge carriers. Electrons are majority charge carriers in case of NPN transistor while holes are majority charge carriers in case of PNP transistors.
• Most of the professional prefer NPN transistor over PNP transistor because conduction carried out by the mobility of electrons is better than conduction through mobility of holes.
• These NPN and PNP bipolar junction transistors are current controlled devices and are different than unipolar MOSFET that is a voltage controlled device.

Applications

• This transistor is mainly used for general purpose amplification.
• In many applications, this transistor behaves as a simple switch. When a voltage is applied at the base side, it gets biased and transistor behaves as an ON switch. When there is no voltage at the base side, it won't get biased and the transistor behaves as an OFF switch.