2N4401 NPN Transistor : Pin Configuration & Its Working

The 2N4401 NPN transistor is a commonly used component in different applications. It is available in a small package with some very excellent features. This kind of NPN transistor is mainly designed to use like a switch and medium power amplifier. This transistor includes three layers like N, P & N and three terminals like emitter, base, and collector. In this NPN transistor, the P-doped layer is arranged between two N-doped layers. This article discusses an overview of the 2N4401 transistor and its working with applications.

What is 2N4401 NPN Transistor?

2n4401 NPN transistor is called a bipolar junction transistor (BJT) because the conduction of this transistor can be carried out through both charge carriers like electrons and holes. However, the majority of charge carriers in this transistor will be electrons. This transistor is mainly used in general purpose applications like switching, amplification, and many more.

2N4401 NPN Transistor
2N4401 NPN Transistor

In this transistor, the large current at the emitter terminal is controlled through the small current at the base terminal. In this transistor, the two N-layers signify the two terminals like emitter and collector whereas P-layer signifies the base terminal respectively. So this transistor is known as a current-controlled device.

In this transistor, the base terminal is positive as compared to the emitter terminal. Once a positive voltage is provided at the base terminal of this transistor, the transistor will be biased & allows the flow of current from the emitter terminal to the collector terminal. Here, the emitter terminal generates the electrons. After that, the collector and base terminals will control the number of electrons.

Pin Configuration

The pin configuration of the 2N4401 NPN transistor includes the following. This transistor includes three terminals where each terminal and its purpose are discussed below.

2N4401 Transistor Pin Configuration
2N4401 Transistor Pin Configuration
  • Pin1 (Emitter): This terminal is connected to GND normally and by using this terminal, the flow of current will drain out.
  • Pin2 (Base): This terminal is used to control the transistor biasing by turn ON/OFF the transistor
  • Pin3 (Collector): This terminal is connected to load where the current supplies throughout this terminal.

Features & Specifications

The features and specifications of the 2N4401 NPN transistor include the following.

  • The Transistor family is NPN
  • Majority charge carriers are electrons
  • Minority charge carriers are holes
  • Includes three layers (N,P &N) & three terminals (E, B & C)
  • It is a general-purpose transistor
  • When the collector current is 10mA, the gain of the high DC is 80
  • Collector current of IC is 500mA
  • Collector emitter voltage (VCE) is 40 V
  • Collector base voltage (VCB) is 60 V
  • Breakdown voltage from emitter to base (VBE) is 6V
  • The frequency of transition is 100MHz
  • The available package is To-92
  • Operating temperature ranges from > -55 C < +150 C

Equivalent 2N4401 transistors are 2N3904 and 2N22A. Alternative 2N4401 transistors are BC636, BC547, BC549, BC639, 2N3055, 2N3906, 2N2369, 2N3904, 2N551 & 2SC5200.


How to use 2N4401 NPN Transistor?

The 2N4401 NPN transistor is available in three configurations mainly CE (common-emitter), CB (common base), and CC (common collector). Here the voltage supply at the collector terminal is maximum as compared to the voltage at the base terminal.

The CE configuration is used for amplification purposes mostly as it generates the necessary voltage as well as gain of power. This configuration assists in enhancing the input signal through 20dB which is almost 100 times above the input signal.

The combination of current at the base & collector terminals is equal to the current at the emitter terminal. Here, the differentiation of two terminals like emitter & collector can be done based on their doping concentration & size. Here, the emitter terminal is doped highly whereas the collector terminal is doped lightly.


In this transistor, the gain of forward current is represented with beta (β) and is a fraction between collector current (IC) & base current (IB). here, this ‘β’ is called an amplification factor and its value ranges from 20 to 1000 however its typical value is 200.

The gain of current for this transistor can be specified through alpha (α) and it is a fraction between collector current (IC) emitter current (IE). Here, the value of Alpha mainly ranges from 0.95 to 0.99 but in most of the applications, its typical value is considered as a unity.

Moisture Sensor Switch Circuit

The simple application circuit of the 2N4401 NPN transistor is a moisture sensor switch which is shown below. This is a simple moisture sensor circuit, used to switch equipment on a fixed range of moisture content within different substances like wood, soil, plant, etc.

The required components to build this moisture sensor circuit are; DC supply 6V, two probes, 6V relay, 1N4007 diode, 2N4401 NPN transistor & 300k variable resistor.

Moisture Sensor Switch with 2N4401 Transistor
Moisture Sensor Switch with 2N4401 Transistor

In this circuit, the moisture can be detected from the substance using two probes. The circuit can be adjusted by using a variable resistor to activate the relay on your preferred moisture range. A transistor works like a switch for the relay, so we can connect any load using the relay to control through this circuit.

This circuit working is very simple due to fewer components used. Once the two probes in this circuit detect the moisture of the substance then it allows the voltage supply throughout it to activate the transistor so that the relay will be activated. So the load which is connected to the relay will be activated immediately. This circuit operates with 6V/12V and the relay within this circuit must have a similar value to the input voltage.

Where to use 2N4401 Transistor/Applications

The 2N4401 NPN BJT is equivalent to the 2N2222 NPN transistor. This transistor is commonly used in different applications but the main difference between the 2N4401 & 2N222 transistors are; 2N4401 transistor allows current at collector terminal upto 500mA & it has 652mW of power dissipation. So it is applicable in medium loads as compared to 2N2222.

So this NPN transistor is used to switch different loads or used for amplification. In several applications, the 2N4401 transistor performs like a switch. Once voltage supply is provided at the base terminal then the transistor will get biased and works as an ON switch. Similarly, when there is no voltage supply at the base terminal then the transistor works like an OFF switch.

Some of the applications of 2N4401 NPN Transistor mainly includes the following

  • Audio Pre-amplifiers
  • Rectifier circuits
  • Sensor Circuits
  • Inverter circuits
  • Stages of Audio Amplifier
  • It is used in different switching applications.
  • It used to switch loads below 500mA
  • It can be used for switching maximum current loads like upto 500mA
  • Used to control the speed of a motor
  • RF circuits below 250MHz
  • Used as a Darlington pair transistor

Thus, this is all about an overview of the 2N4401 transistor datasheet which includes its pin configuration, specifications, circuit working, and its applications. The major difference between PNP & NPN transistors is the majority of charge carriers. The majority of charge carriers in NPN are electrons whereas, in PNP majority of charge carriers are holes. As compared to PNP, most of the manufacturers use NPN transistors due to conduction carried out through the electrons mobility is superior. Here is a question for you, what is a bipolar junction transistor?

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