Everything about 2N4401 NPN Transistor: Datasheet, Pinout, and Equivalent

The 2N4401 NPN transistor is a frequently utilized component in various applications, presenting itself in a compact package with commendable features. Designed primarily for deployment as a switch and a medium-power amplifier, this transistor boasts three layers—N, P, and N—and is equipped with three terminals: emitter, base, and collector. The P-doped layer is strategically positioned between the two N-doped layers in this NPN transistor configuration. This article provides an overview of the 2N4401 transistor, delving into its functionality and applications.

What is 2N4401 NPN Transistor?

The 2N4401 functions as an NPN transistor. Consequently, with the base pin grounded, the collector and emitter remain open (reverse-biased), transitioning to a closed state (forward-biased) when a signal is applied to the base pin. The transistor's amplification capacity is determined by its gain value, hfe, set at 500. Limiting the current to 500mA is crucial to avoid overloading the transistor, as the maximum allowable current through the Collector pin is 800mA.

 

A current must be supplied to the base pin for proper biasing, constrained to 5mA (IB). In a fully biased state, the transistor, known as the Saturation Region, permits a maximum current flow of 800mA between the collector and emitter. During this stage, the permissible voltage across the Collector-Emitter (V­CE) or Base-Emitter (VBE) ranges from 200mV to 900mV. Upon removal of the base current, the transistor enters the fully off state, termed the Cut-off Region, with a Base-Emitter voltage of approximately 660mV.

2N4401 Pinout

The 2N4401 NPN transistor exhibits a pin configuration characterized by three terminals. Each terminal, along with its designated function, is elaborated upon below.

Pin Configuration

Pin No.	Pin Name	Description
1	Emitter	Current Drains out through emitter, normally connected to ground
2	Base	Controls the biasing of transistor, Used to turn ON or OFF the transistor
3	Collector	Current flows in through collector, normally connected to load

Features & Specifications

• High DC Current Gain (hFE), typically 80 at IC=10mA

• Sustained Collector Current (IC): 500mA

• Maximum Collector Current: 600 mA

• Collector-Emitter Voltage (VCE): 40 V

• Collector-Base Voltage (VCB): 60V

• Emitter-Base Breakdown Voltage (VBE): 6V

• Power Dissipation: 625 mW

• Transition Frequency: 100MHz

• DC Current Gain (hFE): 20 - 300

• Storage & Operating Temperature: -55 to +150 Centigrade

• Available in To-92 Package

2N4401 Circuit Diagram

The circuit diagram of the 2N4401 is depicted in the figure below.

The voltage at the collector side surpasses that at the base side. This transistor is available in three main configurations: common base, emitter, and collector. The common emitter configuration is primarily used for amplification, offering the necessary voltage and power gain. This configuration enhances the input signal by 20dB, nearly 100 times more than the input signal.

The emitter current is a combination of base and collector current. Collector and emitter can be distinguished by their size and doping concentration, with the emitter being highly doped and the collector lightly doped.

The forward current gain of the transistor, denoted by beta (ß), represents the ratio between collector current and base current. Beta is an amplification factor measuring the amplified current, and its value ranges between 20 and 1000, with a standard value of 200. Beta is a unitless ratio of two currents.

The current gain of this transistor is represented by alpha (α), which is the ratio between collector current and emitter current. Alpha values range between 0.95 and 0.99, with its value often considered as unity.

2N4401 Test Circuits

2N4401 Saturated Turn-On Switching Timer

2N4401 Saturated Turn-Off Switching Timer

Moisture Sensor Switch Circuit

The uncomplicated application circuit featuring the 2N4401 NPN transistor is a moisture sensor switch, as illustrated below. This circuit is a straightforward moisture sensor, enabling equipment activation within a specified moisture range in diverse materials such as wood, soil, and plants.

The essential components for constructing this moisture sensor circuit include a 6V DC power supply, two probes, a 6V relay, 1N4007 diode, 2N4401 NPN transistor, and a 300k variable resistor.

In this arrangement, moisture is gauged within the substance using two probes. The circuit's sensitivity can be fine-tuned via the variable resistor to trigger the relay within the desired moisture threshold. The transistor functions like a switch for the relay, facilitating the control of any load connected to the relay through this circuit.

The operational principle of this circuit is straightforward, attributed to the minimal components employed. Once the two probes detect moisture in the substance, they permit the voltage supply, activating the transistor and energizing the relay. Consequently, the connected load activates promptly. This circuit operates effectively with 6V/12V, and the relay within the circuit must align with a comparable value to the input voltage.

2N4401 Alternative NPN Transistors

2N4401 Alternatives include BC549, BC636, BC639, BC547, 2N2369, 2N3055, 2N3904, 2N3906, 2SC5200 and 2N5551.

2N4401 Equivalents

2N3904 and 2N2222A can equivalent to 2N4401.

2N4401 PNP Complementary

2N4403: The 2N4401 and 2N4403 transistors form a PNP complementary pair, offering similar electrical characteristics. The 2N4403 is the NPN counterpart to the 2N4401.

Absolute Maximum Ratings of 2N4401

The absolute maximum ratings of the 2N4401 are illustrated in the figure below.

• The Collector-Emitter and Collector-Base voltages are specified as 40 V and 60 V, respectively. 

• Exceeding these absolute maximum ratings can result in damage to the device.

• Additionally, if stresses are applied for an extended period, they may impact the device's reliability.

Where 2N4401 Transistor is Used

The 2N4401 transistor is similar to the commonly used NPN transistor, 2N2222. However, two crucial features set the 2N4401 apart from the 2N2222. The 2N4401 can accommodate a collector current of up to 500mA and has a power dissipation of 652mW, making it suitable for medium loads compared to the 2N2222. It can drive loads more effectively than the BC547.

If you are searching for an NPN transistor capable of switching loads or providing moderate amplification, the 2N4401 might be the ideal choice for your project.

How to use 2N4401 Transistor

Like all others, this transistor can function as a switch and an amplifier. The Base-Emitter voltage of this transistor is 6V, so you need to supply this voltage across the base and emitter to induce a base current. This forward-biases the transistor, closing the connection between the collector and emitter. However, it's crucial to note the presence of the Base resistor, also known as the current-limiting resistor. As the name implies, this resistor restricts the current flowing through the transistor to prevent damage. The value for this resistor can be calculated using the formula:

RB = VBE / IB

To simplify, I've presented a basic circuit to illustrate using a transistor as a switch. Actual circuit modifications may be necessary. I've chosen a base voltage of 5V and a 1K resistor as the current-limiting resistor.

It's important to highlight that the motor in this setup draws about 500mA from the 12V power source. Since the 2N4401 has a collector current rating of up to 500mA, this circuit is feasible. If a BC547 were used, the transistor could be damaged.

2N4401 Applications

Suitable for switching high-current loads (up to 500mA), the 2N4401 transistor offers versatile applications, including:

• Various switching applications.

• Speed control of motors.

• Inverter and other rectifier circuits.

• Integration into Darlington Pair configurations.

• Sensor circuits.

• Deployment in audio preamplifiers.

• Use in audio amplifier stages.

• Efficient switching of loads under 500mA.

• Reliable performance in RF circuits under 250MHz.

2N4401 Package

2D-Model and Dimensions

What's the Difference between 2N4401 and 2N2222?

The 2N4401 transistor closely resembles the commonly used 2N2222 NPN transistor. Despite their similarities, two crucial distinctions set the 2N4401 apart from the 2N2222. The 2N4401 comes with a collector current limit of 500mA and a power dissipation of 652mW, rendering it suitable for medium loads compared to the 2N2222. However, it exhibits the capability to drive loads greater than the BC547.

What's the Difference between 2N4401 and 2N3904?

The 2N3904 and the 2N4401 are highly similar in all specifications. While the 2N4401 boasts a higher current rating, overall, they are similar in price and other features. When examining various performance parameters, it becomes apparent that the 2n3904 is more finely tuned for operation at lower currents than the 2n4401. In many applications, the difference is insufficient to warrant attention, making them interchangeable for such purposes.

Advantages & Disadvantages

Advantages

The 2N4401 enjoys a prominent status in the field of electronics. Let's delve into the reasons behind the widespread admiration for this diminutive device within the realm of electronics.

• Versatility

The 2N4401 is a versatile component, adept at serving as a switch, an amplifier, or even both in specific applications. This adaptability renders it a favored choice in circuit design.

• Durability

Despite its compact dimensions, the 2N4401 exhibits robustness. It can endure a broad range of temperatures and boasts high resilience to electrical noise, establishing itself as a dependable component in various electronic systems.

Disadvantages

Like any electronic component, the 2N4401 transistor has limitations that must be considered during circuit design.

• Handling High Power

The 2N4401 is not intended for high-power applications. It is engineered to manage low to moderate power levels, making it unsuitable for systems requiring high power.

• Sensitivity to Environmental Conditions

Despite its general resilience, the 2N4401 can exhibit sensitivity to extreme environmental conditions. Prolonged exposure to high temperatures or moisture has the potential to impact its performance gradually.

2N4401 Datasheet

Download 2N4401 datasheet PDF.

Conclusion

The 2N4401 NPN transistor is a versatile component widely used in electronics for signal amplification and switching applications. Understanding its specifications, pinout, and characteristics is crucial for designing effective and reliable circuits. Whether you're building amplifiers, switching circuits, or oscillators, the 2N4401 is a valuable tool in electronic design.

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