2N4921 Pinout, Equivalent, Application, Datasheet

The 2N4921 pinout and electrical performance make it a reliable medium-power NPN transistor ideal for switching and amplification tasks. With its TO-126 package, 40V voltage rating, and 1A current handling, it fits well in circuits requiring moderate gain and efficient heat dissipation. Its compact design and stable characteristics make it a common choice for driver stages, regulators, and low-frequency amplifier applications.

Introduction to 2N4921 NPN Transistor

The 2N4921 is an NPN silicon power transistor designed primarily for low-to-medium power applications. It offers a good balance between collector current, voltage capability, and power dissipation, which makes it versatile for use in both consumer and industrial electronics. The transistor features a maximum collector-emitter voltage of 40V and can handle up to 1A collector current, providing robust performance for small power loads.

With a TO-126 case, the 2N4921 ensures efficient thermal transfer, allowing safe operation at up to 30 watts when properly heat-sinked. It is commonly used in relay drivers, DC motor control circuits, small amplifiers, and voltage regulators.

2N4921 NPN Transistor

Pinout of 2N4921

Understanding the 2N4921 Pinout Configuration

The transistor follows a standard E–C–B pin configuration when viewed from the front (leads facing downward). Proper pin identification is crucial to prevent reverse connection, which could damage the transistor or affect circuit functionality.

Pin Configuration of 2N4921 Pinout

Key Features of 2N4921 Transistor

• Medium power NPN silicon transistor
• High current handling up to 1A
• Suitable for switching and amplification applications
• Stable performance under thermal stress
• Compact TO-126 package with good heat dissipation
• Reliable for general-purpose and industrial circuits

2N4921 Transistor Datasheet and Specifications

• Transistor Type: NPN Silicon
• Collector–Emitter Voltage (Vce): 40V
• Collector–Base Voltage (Vcb): 40V
• Collector Current (Ic): 1.0A
• Power Dissipation (Ptot): 30W
• Package Type: TO-126
• Pin Configuration: Emitter–Collector–Base (E–C–B)
• Transition Frequency (fT): Typically around 3 MHz
• DC Current Gain (hFE): 40–160 (depending on collector current)
• Junction Temperature (Tj): 150°C (maximum)

Working Principle of 2N4921 NPN Transistor

As an NPN transistor, the 2N4921 functions by allowing current to flow from collector to emitter when a small biasing current is applied to its base terminal. In this mode, it acts as a controlled current amplifier. The transistor’s internal structure allows it to efficiently manage moderate power levels while maintaining stability even at elevated temperatures, making it suitable for both linear and switching operations.

More Circuit Layouts

Typical Applications of 2N4921

• Audio and signal amplifier stages
• DC motor drivers and control circuits
• Voltage regulators and DC switching
• Relay and solenoid drivers
• General-purpose small power circuits
• Battery-powered devices requiring medium load control

Equivalent Transistors and Alternatives

Several transistors can substitute the 2N4921 in circuits with similar ratings and pinout. Common equivalents include:

• BD139 (slightly higher voltage rating, same current range)
• MJE180 (medium power NPN with similar characteristics)
• 2N2222A (for lower current versions)
• TIP29A (for higher power margin and TO-220 case)

Always ensure pin configuration and package compatibility when using equivalents.

Frequently Asked Questions (FAQ)

What is the 2N4921 transistor used for?

It’s used for switching, amplification, and power control in audio, motor, and voltage regulator circuits.

What type of transistor is 2N4921?

It is an NPN silicon transistor.

What is the 2N4921 pin configuration?

It has Emitter–Collector–Base (E–C–B) pin sequence in the TO-126 package.

What is the complementary transistor for 2N4921?

The complementary PNP transistor is 2N4924.

Can I use BD139 instead of 2N4921?

Yes, BD139 can be used as a replacement in most circuits with similar ratings, but check the pinout before use.

Conclusion

The 2N4921 transistor provides reliable and efficient performance for medium-power applications. Its 40V rating, 1A collector current, and 30W power handling make it an excellent choice for small amplifier circuits and controlled switching tasks. With its E–C–B configuration in the TO-126 package, it fits perfectly into designs where compact power transistors are required. Pairing it with its PNP complement 2N4924 allows designers to build balanced, efficient amplifier or driver stages.

Datasheet & Pinout of 2N4921 PNP Transistor

Click the following Button to download the datasheet of 2N4921 Transistor :

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