onsemi 2N4124TAR

Overview

2N4124TAR from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor designed for low-power amplification and switching in discrete analog and digital circuits. It delivers DC current gain (h_FE) of 120–360 at I_C = 2 mA, supports 100 MHz small-signal bandwidth (f_T), and operates with V_CEO = 25 V and continuous I_C = 200 mA - commonly used in signal conditioning stages of industrial sensor interfaces and low-voltage logic-level translators.

For engineers reviewing the 2N4124TAR 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 @ 50 mA), noise figure (5.0 dB @ 100 µA), and guaranteed f_T ≥ 300 MHz - all critical for audio preamp, pulse generator, and low-noise amplifier design.

Technical Context

The 2N4124TAR is a silicon planar epitaxial NPN transistor optimized for linear amplification and saturated switching. Its f_T = 300 MHz and h_fe = 120–480 (at 2 mA) support high-fidelity small-signal amplification up to VHF band edges, while V_BE(sat) = 0.95 V and β = 10 switching condition confirm robust turn-on behavior in digital gate drivers.

Thermal performance is defined for FR-4 PCB mounting (1.6" × 1.6" × 0.06"), with R_θJA = 200 °C/W and maximum T_J = +150 °C. Its C_obo = 4.0 pF and C_ibo = 8.0 pF enable stable high-frequency biasing without unintended resonance in tuned amplifier stages.

Key Specifications

Pinout & Package

2N4124TAR is packaged in TO-92 - a through-hole plastic case with 3 leads, rated for 625 mW total dissipation at 25°C ambient and derated linearly above that temperature.

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 2N4124TAR offers guaranteed minimum f_T, tighter h_FE binning at low I_C, and TO-92 mechanical robustness - making it preferable for bench-testable, medium-frequency analog designs requiring repeatable performance.

Availability

2N4124TAR is available at Aetrix Electronics and suitable for industrial sensor interfaces, audio pre-amplifier stages, and digital logic level translation requiring stable component supply and long-term manufacturability.

Supply support for 2N4124TAR 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 devices before its acquisition by ON Semiconductor in 2016.

The 2N4124TAR belongs to Fairchild's legacy general-purpose bipolar transistor family, engineered for reliability in analog signal conditioning and low-speed digital switching across industrial and consumer equipment.

FAQ

What is the maximum operating junction temperature for the 2N4124TAR?

The 2N4124TAR has a maximum operating junction temperature (T_J) of +150 °C, as specified in its Absolute Maximum Ratings table. This limit applies under steady-state conditions with proper PCB thermal design - specifically a 1.6" × 1.6" × 0.06" FR-4 board. Exceeding this temperature risks permanent degradation of h_FE and increased leakage currents. Derating begins at 25 °C ambient, with PD reduced by 5.0 mW/°C for the TO-92 package.

Does the 2N4124TAR support high-frequency amplification up to 100 MHz?

Yes, the 2N4124TAR supports high-frequency amplification up to 100 MHz, as confirmed by its minimum f_T of 300 MHz and typical small-signal current gain (h_fe) > 120 at 100 MHz. Measured data shows usable gain margin at 100 MHz under standard test conditions (I_C = 10 mA, V_CE = 20 V), making the 2N4124TAR suitable for VHF-band preamplifier and RF detector stages where linearity and low noise are required.

What is the typical noise figure of the 2N4124TAR and under what conditions is it measured?

The typical noise figure of the 2N4124TAR is 5.0 dB, measured at I_C = 100 µA, V_CE = 5.0 V, R_S = 1.0 kΩ, and frequency range 10 Hz to 15.7 kHz. This value reflects its suitability for low-level audio and sensor signal amplification where preserving signal-to-noise ratio is critical. The 2N4124TAR maintains this NF across –40°C to +125°C ambient, supporting stable performance in unregulated industrial enclosures.

Can the 2N4124TAR be used as a saturated switch in 5 V logic circuits?

Yes, the 2N4124TAR can be used as a saturated switch in 5 V logic circuits. At I_C = 50 mA and I_B = 5 mA (β = 10), its V_CE(sat) is guaranteed ≤ 0.3 V, ensuring sufficient logic-high margin for TTL and CMOS inputs. Its V_BE(sat) = 0.95 V allows direct drive from 3.3 V or 5 V MCU GPIOs with appropriate base resistors. The 2N4124TAR's fast turn-on (<10 ns) and fall time (<50 ns) further support reliable digital switching up to 10 MHz.

How does the thermal resistance of the 2N4124TAR compare between junction-to-case and junction-to-ambient?

The 2N4124TAR has R_θJC = 83.3 °C/W and R_θJA = 200 °C/W when mounted on a standard 1.6" × 1.6" × 0.06" FR-4 PCB. This 2.4× difference highlights the dominant role of PCB copper area in heat dissipation. For example, at 350 mW dissipation, junction temperature rise above ambient would be ~70 °C - well within the +150 °C limit if ambient stays below +80 °C. The 2N4124TAR's thermal profile makes it viable for sealed enclosures without forced airflow, provided layout follows Fairchild's recommended pad geometry.