2N4123 NPN General Purpose Transistor

General Purpose NPN Bipolar Junction Transistor

The Fairchild Semiconductor 2N4123 is a highly reliable, single NPN silicon bipolar junction transistor designed for small-signal amplification and high-speed digital switching applications. Fabricated using advanced planar epitaxial processing technology, this discrete semiconductor provides exceptional linearity and consistent electrical performance across a wide operating junction temperature range from -55 degrees Celsius to +150 degrees Celsius. Encapsulated in a standard 3-pin through-hole TO-92 plastic package, the 2N4123 serves as a foundational component for robust analog front-ends, control logic interfaces, and discrete driver stages.

Electrical Characteristics and Thermal Dynamics

Engineered to handle low-to-medium power demands, the 2N4123 features a maximum Collector-Emitter Voltage (VCEO) rating of 30V, a Collector-Base Voltage (VCBO) of 40V, and an Emitter-Base Voltage (VEBO) of 5.0V. It supports a continuous DC collector current (IC) of up to 200mA, making it suitable for driving small loads, relays, and indicators. Thermal management is supported by a total device power dissipation limit of 625 mW at an ambient temperature of 25 degrees Celsius, with a thermal resistance from junction to ambient rating of 200 degrees Celsius per Watt. Dynamic parameters include a minimum DC current gain (hFE) of 50 at 2mA collector current, alongside a transition frequency (fT) reaching up to 250 MHz, ensuring fast switching transitions and low phase distortion in high-frequency applications.

Circuit Applications and Design Integration

The 2N4123 excels across a broad spectrum of commercial, industrial, and educational electronic applications. Common implementations include low-noise audio preamplifiers, active filter circuits, analog signal buffering, and sensor interface signal conditioning. Its rapid response time and high current-gain bandwidth product allow it to function effectively in high-speed logic gate switching, VHF oscillators, and pulse generation circuits. Board layout engineers benefit from the standard TO-92 EBC lead configuration, which simplifies breadboard prototyping, automated through-hole insertion, and PCB routing for embedded control units, power management sub-circuits, and instrumentation modules.