Today, I am going to unlock the details on the Introduction to 2n4400. It is an NPN (negative-positive-negative) bipolar transistor which is mainly designed for general purpose amplification and switching applications.
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It is mainly composed of three terminals called emitter, base, and collector, where small current at the base side is used to control large current at the emitter and collector side.
This NPN transistor consists of two N doped layers which cover the one P doped layer. The P terminal shows the base of the transistor while other two terminals show collector and emitter respectively.
Most of the old transistors were made of germanium. However, new transistors are made from silicon.
When a voltage is applied at the base terminal, it triggers electron reaction, gets biased, draws current which is then used to control large current at the collector and emitter side.
All three terminals are different in terms of size and doping concentration. An emitter is highly doped as compared to collector and base while a base is lightly doped. However, a voltage at the collector side is more than the voltage at the base side.
Actually, movement of electrons acts like a bridge between emitter and collector.
2n4400 is also referred as bipolar junction transistor where conduction is carried out by the movement of electrons and holes, however, majority charge carriers are electrons.
Pinout of the 2n4400 is shown in the figure below.
The base controls the number of electrons and draws current which is then used to control large current at the other terminals. This process is used for amplification purpose.
Circuit Diagram of 2n4400
Following figure shows the circuit diagram of the 2n4400.
Emitter current is equal to the sum of base and collector current because doping concentration of emitter is more than both collector and base.
This transistor can be configured into three configurations called common base configuration, common collector configuration, and common emitter configuration. Common emitter configuration is mostly used for the amplification purpose because it provides the required power and voltage for the amplification purpose.
Forward current gain is an important feature in this NPN transistor, which is also called amplification factor that defines the measure of current being amplified. It is called beta ß, and it is a ratio between collector current and base current. Beta value is a ratio between two currents so it exhibits no unit.
Beta value ranges between 20 to 1000. However, standard value of beta is 200.
Current gain is another important factor which is called alpha a and it is a ratio between collector current and emitter current. Alpha value ranges between 0.95 to 0.99. However, most of the time alpha value is taken as unity.
Transistors always operate in forward biased mode. If we interchange emitter and collector and makes it reverse biased, then the value of alpha and beta will be much lesser than they will be in forward biased mode.
In the ON state current will flow from emitter to collector and free movement of electrons from the base side is used to control the current between emitter and collector.
Absolute Maximum Ratings
Following figure shows the absolute maximum ratings of 2n4400
It is important to note that, these are the stress ratings, which if exceed from the absolute maximum ratings, can damage the device quality and overall functionality of the device.
It is recommended to apply these stress ratings for the specific period of time given by the manufacturer. If these ratings are applied for a maximum period of time they can affect the device reliability.
This NPN transistor is widely used for general purpose amplification and switching purpose.
That's all for today. I have tried my best to cover each and everything related to this amplification transistor. However, if still you feel skeptical or have any question you can ask me in the comment section below. I'd love to help you based on my best of my knowledge and expertise.
I'd suggest you have a look at PNP transistor where holes are majority carriers, different than NPN transistor where electrons are majority carriers.
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I am Syed Zain Nasir, the founder of The Engineering Projects (TEP). I am a
programmer since 2009 before that I just search things, make small projects and now I am sharing my
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