onsemi 2N4124TF

Overview

2N4124TF from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) optimized for low-noise amplification and switching applications, with DC current gain (h_FE) of 120–360 at I_C = 2 mA, V_CE = 1 V; V_CEO = 25 V; f_T = 300 MHz; and noise figure of 5.0 dB at 10 Hz–15.7 kHz. It operates across –55°C to +150°C and supports 100 mA switching and 100 MHz RF amplification in consumer audio, signal conditioning, and discrete logic interfaces.

For engineers reviewing the 2N4124TF datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92 package thermal resistance (R_θJA = 200°C/W), saturation voltage (V_CE(sat) = 0.3 V @ I_C = 50 mA), input/output capacitance (C_ibo = 8.0 pF, C_obo = 4.0 pF), and guaranteed h_FE range - all critical for analog front-end design, discrete amplifier staging, and low-power switching circuits.

Technical Context

The 2N4124TF is a silicon planar epitaxial NPN BJT designed for linear amplification and saturated switching. Its f_T = 300 MHz and h_fe = 120–480 (at 1 kHz) support mid-band RF and audio-frequency small-signal gain, while V_BE(sat) = 0.95 V and V_CE(sat) = 0.3 V enable efficient low-voltage switching in discrete logic and driver stages.

Thermal performance is defined for FR-4 PCB mounting (1.6" × 1.6" × 0.06"), with R_θJA = 200°C/W and maximum junction temperature of 150°C. Absolute ratings include V_CBO = 30 V, V_EBO = 5.0 V, and I_C = 200 mA continuous - confirming suitability for general-purpose analog and digital interfacing where robustness and predictable gain are required.

Key Specifications

Pinout & Package

2N4124TF is housed in a through-hole TO-92 package (JEDEC TO-92 variant), with leads arranged in standard C-B-E configuration when viewed from flat side with leads down. Thermal derating begins above 25°C at 5.0 mW/°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN general-purpose amplifier applications.

Compared with MMBT4124 and 2N3904, the 2N4124TF offers superior thermal management in TO-92 (R_θJA = 200°C/W vs. 357°C/W) and tighter h_FE control - making it preferable for analog-intensive, manually assembled, or thermally demanding applications where gain predictability and noise floor matter.

Availability

2N4124TF is available at Aetrix Electronics and suitable for audio pre-amplifier stages, discrete logic level shifters, RF signal buffers, and industrial sensor interfaces requiring stable component supply and long-term manufacturability.

Supply support for 2N4124TF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016; its legacy BJT portfolio remains widely deployed and supported.

The 2N4124TF belongs to Fairchild's general-purpose NPN amplifier family, engineered for broad utility in analog signal conditioning, switching, and interface circuits where reliability, gain consistency, and low noise are prioritized over ultra-high speed or integrated functionality.

FAQ

What is the maximum collector current rating for the 2N4124TF?

The 2N4124TF has a continuous collector current rating (I_C) of 200 mA per its Absolute Maximum Ratings table. This value assumes operation at T_A = 25°C with proper PCB thermal relief; derating is required above 25°C at 5.0 mW/°C. The device is commonly used at ≤100 mA for reliable switching and amplification, aligning with its specified dynamic range.

Does the 2N4124TF have a guaranteed minimum h_FE at high collector currents?

Yes - the 2N4124TF guarantees h_FE ≥ 60 at I_C = 50 mA and V_CE = 1.0 V, in addition to the 120–360 range at I_C = 2.0 mA. This dual-point specification ensures usable gain even under moderate switching loads, supporting robust bias design in both linear and saturated operating regions.

Is the 2N4124TF suitable for audio-frequency low-noise amplification?

Yes - the 2N4124TF specifies a noise figure (NF) of 5.0 dB at I_C = 100 µA, V_CE = 5.0 V, R_S = 1.0 kΩ, and 10 Hz–15.7 kHz bandwidth. This measured value, combined with its low C_ibo and stable h_FE, makes it appropriate for microphone preamps, sensor signal conditioning, and other low-level analog gain stages where noise contribution must be minimized.

What is the thermal resistance (R_θJA) of the 2N4124TF in its TO-92 package?

The 2N4124TF exhibits R_θJA = 200°C/W when mounted on a standard FR-4 PCB (1.6" × 1.6" × 0.06"). This value reflects junction-to-ambient conduction and convection under defined test conditions; actual thermal performance may vary with board copper area, airflow, and enclosure design. For sustained >150 mW dissipation, heatsinking or forced cooling should be considered.

Can the 2N4124TF replace the 2N2222A in existing designs?

The 2N4124TF shares similar topology and many electrical parameters with the 2N2222A (e.g., V_CEO = 25 V, f_T ≈ 300 MHz), but differs in guaranteed h_FE range (120–360 vs. 35–300) and noise figure (5.0 dB vs. unspecified). It can serve as a functional upgrade in low-noise or gain-critical roles, but validation of bias point stability and thermal margin is recommended before drop-in replacement.