onsemi 2N4125TFR

Overview

2N4125TFR from Fairchild Semiconductor is a PNP general-purpose amplifier and switch optimized for low-to-moderate current linear amplification and switching applications, with V_CEO = 30 V, I_C = 200 mA continuous, h_FE = 50–150 at I_C = 2 mA, and TO-92 package. It operates across –55°C to +150°C and supports collector currents from 10 µA to 100 mA in discrete analog stages and digital logic interfaces.

For engineers reviewing the 2N4125TFR datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, 30 V breakdown ratings, thermal resistance (R_θJA = 200 °C/W), saturation performance (V_CE(sat) = 0.4 V @ I_C = 50 mA), and suitability for low-noise audio preamplifier or relay driver circuits.

Technical Context

The 2N4125TFR is a silicon planar epitaxial PNP bipolar junction transistor designed for general-purpose linear amplification and saturated switching. Its DC current gain (h_FE) varies from 50 to 150 depending on operating point, and small-signal h_fe reaches 200 at 1 kHz but drops to 2.0 at 100 MHz - confirming its primary use in audio and DC/low-frequency signal paths.

It features low noise figure (NF = 5.0 dB @ f = 10 Hz–15.7 kHz, I_C = 100 µA, R_S = 1 kΩ), tight V_BE(sat) = 0.95 V @ I_C = 50 mA, and robust thermal design with T_J(max) = 150°C and derating of 5.0 mW/°C above 25°C - enabling reliable operation in ambient temperatures up to +125°C at full power.

Key Specifications

Pinout & Package

2N4125TFR is housed in a through-hole TO-92 plastic package with standard PNP lead configuration: Emitter (pin 1), Base (pin 2), Collector (pin 3) - viewed with flat side facing outward and leads pointing down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA92 and BC557, the 2N4125TFR delivers balanced performance: moderate voltage (30 V), verified 200 mA capability, consistent h_FE, and industry-standard TO-92 compatibility - making it ideal for cost-sensitive, thermally stable, mid-current analog and switching roles.

Availability

2N4125TFR is available at Aetrix Electronics and suitable for industrial control panels, audio signal conditioning circuits, and embedded relay interface modules requiring stable component supply and long-term manufacturability.

Supply support for 2N4125TFR 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.

The 2N4125TFR belongs to Fairchild's legacy general-purpose bipolar transistor family, engineered for reliability in linear amplification and robust switching across industrial, instrumentation, and consumer electronics.

FAQ

What is the pin configuration of the 2N4125TFR?

The 2N4125TFR uses a standard TO-92 package with Emitter (pin 1), Base (pin 2), and Collector (pin 3) - identified with the flat side facing the viewer and leads downward. This matches JEDEC TO-92 outline and is confirmed in Fairchild's Rev A datasheet for 2N4125TFR. Pinout is identical across all TO-92 variants of this part number, including the TFR suffix denoting tape-and-reel packaging.

Does the 2N4125TFR support switching applications?

Yes, the 2N4125TFR is explicitly rated for switching use with V_CE(sat) = 0.4 V at I_C = 50 mA and I_B = 5 mA, and t_on/t_off specified down to tens of nanoseconds. Its PNP architecture allows direct interfacing with microcontroller GPIOs driving relay coils or LED strings. The 2N4125TFR datasheet confirms pulsed operation up to 300 µs duty cycle, supporting both linear and saturated-mode designs.

What is the maximum operating temperature for the 2N4125TFR?

The 2N4125TFR has a specified junction temperature range of –55°C to +150°C, with thermal resistance R_θJA = 200 °C/W. At ambient temperatures up to +75°C, it can sustain full 625 mW dissipation; above that, linear derating applies (5.0 mW/°C). This makes the 2N4125TFR suitable for sealed enclosures and non-ventilated industrial environments where passive cooling is the only option.

How does the noise performance of the 2N4125TFR compare to other general-purpose transistors?

The 2N4125TFR specifies NF = 5.0 dB at 10 Hz–15.7 kHz with I_C = 100 µA and R_S = 1 kΩ - competitive with low-noise PNP devices like the BC557 (NF ≈ 5–10 dB) and superior to high-voltage types such as MPSA92 (NF > 10 dB). Its low C_ib = 10 pF and stable h_fe further reduce broadband noise contribution, making the 2N4125TFR a preferred choice for first-stage audio amplification where signal integrity is critical.

Is the 2N4125TFR RoHS compliant?

Yes, the 2N4125TFR is RoHS compliant per Fairchild's product change notification and packaging documentation. The "TFR" suffix denotes tape-and-reel packaging conforming to J-STD-020 moisture sensitivity level (MSL) 1, and the device contains no lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE above threshold limits. Full compliance documentation for the 2N4125TFR is available through Aetrix Electronics' component traceability portal.