2N4123 Pinout, Equivalent, Application, Datasheet

The 2N4123 pinout follows the Emitter–Base–Collector (E–B–C) sequence and it is a general-purpose NPN transistor widely used in low-power signal processing, amplifier, and switching applications. Known for its fast response, high transition frequency, and low noise characteristics, the 2N4123 is a versatile choice for RF circuits, analog signal amplification, and digital switching.

Introduction to 2N4123 NPN Transistor

The 2N4123 is a silicon NPN bipolar junction transistor (BJT) specifically designed for high-speed low-power amplification and switching circuits. It operates efficiently at low voltages and currents, making it ideal for use in audio stages, signal amplifiers, and oscillator circuits.

This transistor is housed in a TO-92 package, providing a compact design suitable for through-hole PCB mounting. It features a maximum collector-emitter voltage of 30 V, collector-base voltage of 40 V, collector current up to 200 mA, and a total power dissipation of 625 mW. The combination of reliability, low cost, and stable performance has made the 2N4123 a popular choice in general electronics and communication circuits.

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2N4123 NPN Transistor

Pinout of 2N4123

Understanding the 2N4123 Pinout Configuration

The 2N4123 pinout is arranged as Emitter–Base–Collector (E–B–C) when viewed from the flat side of the TO-92 package. This configuration simplifies its use in breadboard circuits and small PCB designs.

Pin Configuration of 2N4123 Pinout

Key Features of 2N4123 Transistor

• General-purpose NPN transistor for low-power applications
• Fast switching response suitable for digital circuits
• Excellent gain stability and low noise figure
• Compatible with complementary PNP transistor 2N4125
• Compact TO-92 package for easy prototyping and PCB assembly
• Reliable for high-frequency signal amplification

2N4123 Transistor Datasheet and Specifications

• Collector–Emitter Voltage (Vce): 30 V
• Collector–Base Voltage (Vcb): 40 V
• Emitter–Base Voltage (Veb): 6 V
• Collector Current (Ic): 200 mA
• Total Power Dissipation (Pc): 625 mW
• DC Current Gain (hFE): 40 to 200
• Transition Frequency (fT): 250 MHz (typical)
• Package Type: TO-92
• Polarity Type: NPN
• Pin Configuration: Emitter–Base–Collector (E–B–C)

Working Principle of 2N4123 NPN Transistor

The 2N4123 operates as a current-controlled semiconductor device. A small base current allows a much larger collector current to flow between the collector and emitter terminals. This current amplification property makes it ideal for both switching and amplifying low-level signals.

When used as a switch, applying a small base voltage turns the transistor fully ON (saturation), allowing current through the collector to the load. In amplifier configurations, such as common-emitter stages, it provides linear voltage and current gain for weak signals, making it valuable in audio pre-amps, oscillators, and modulation circuits.

More Circuit Layouts

Typical Applications of 2N4123

• Signal amplification and waveform generation
• Low-power switching circuits
• High-frequency oscillators and modulators
• Audio pre-amplifier stages
• Pulse and waveform shaping circuits
• RF and IF amplifier stages

PNP Complementary Transistor

The complementary PNP transistor for the 2N4123 is the 2N4125. Both are designed as matched pairs for push-pull amplifier configurations or symmetrical switching circuits. The 2N4125 provides mirror performance with opposite polarity, allowing designers to create balanced amplification and efficient analog signal control.

Equivalent Transistors and Alternatives

• 2N3904 (general-purpose NPN equivalent)
• BC547 (low-noise NPN alternative)
• 2N4401 (higher current version)
• S8050 (Asian equivalent with similar ratings)
• PN2222A (slightly higher power rating alternative)

Comparison Summary: 2N4123 vs 2N4125

The 2N4123 (NPN) and 2N4125 (PNP) transistors are complementary devices designed for low-power signal applications. Both share similar voltage, current, and gain characteristics but differ in polarity and current flow direction.

The 2N4123 conducts when a positive voltage is applied to the base relative to the emitter, while the 2N4125 conducts with a negative base bias. This complementary relationship makes them ideal for Class-B amplifier stages, analog signal processing, and digital switching pairs, ensuring balanced operation across both halves of a waveform.

Frequently Asked Questions (FAQ)

What is the maximum voltage rating of 2N4123?

It supports up to 30 V between collector and emitter and 40 V between collector and base.

What is the maximum collector current of 2N4123?

The maximum collector current (Ic) is 200 mA, suitable for small-signal loads.

What is the 2N4123 pinout configuration?

The 2N4123 pinout is Emitter–Base–Collector (E–B–C) when viewed from the flat side of the TO-92 package.

What is the complementary transistor for 2N4123?

The 2N4125 is the complementary PNP transistor for 2N4123.

Can 2N4123 be used for amplification?

Yes, it is commonly used in low-noise signal amplification and audio pre-amplifier circuits.

Conclusion

The 2N4123 NPN transistor is a reliable, low-power, and high-frequency component ideal for signal processing, switching, and amplifier circuits. Its TO-92 package, low noise, and fast transition characteristics make it a strong choice for both hobbyists and professional circuit designers.

With a maximum collector current of 200 mA and power dissipation of 625 mW, it performs efficiently in a wide range of analog and digital circuits, particularly when paired with its PNP complement 2N4125.

Datasheet of 2N4123 NPN Transistor

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