onsemi 2N4125TA

Overview

2N4125TA from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor used for low-to-medium current amplification and switching in analog and digital circuits, with V_CEO = 30 V, I_C = 200 mA continuous, h_FE = 50–150 at I_C = 2 mA, and TO-92 package. It serves in signal conditioning stages of sensor interfaces, discrete logic inverters, and load-switching circuits in industrial control modules.

For engineers reviewing the 2N4125TA datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, 30 V breakdown rating, 200 mA collector capability, thermal resistance (R_θJA = 200 °C/W), and suitability for linear amplification or saturated switching below 100 mA.

Technical Context

This PNP BJT operates in common-emitter or common-base configurations with verified DC current gain (h_FE) ranging from 50 to 150 depending on bias point, and exhibits V_BE(sat) = 0.95 V at I_C = 50 mA / I_B = 5 mA. Its small-signal h_fe reaches 200 at 1 kHz but drops to 2.0 at 100 MHz, confirming audio- and low-RF applicability.

Thermal design is constrained by R_θJA = 200 °C/W and maximum junction temperature of +150 °C, requiring derating above 25 °C at 5.0 mW/°C. Cutoff leakage (I_CBO ≤ 50 nA at V_CB = 20 V) supports stable operation in low-power standby circuits.

Key Specifications

Pinout & Package

2N4125TA is housed in a through-hole TO-92 package with standard PNP lead assignment: Emitter (pin 1), Base (pin 2), Collector (pin 3), viewed with flat side facing outward and leads down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557B and MPSA92, the 2N4125TA offers balanced trade-offs: moderate voltage rating (30 V), verified low-noise performance (5.0 dB), and robust DC gain stability-making it optimal for cost-sensitive, medium-speed analog and switching roles where neither ultra-high gain nor extreme voltage tolerance is needed.

Availability

2N4125TA is available at Aetrix Electronics and suitable for industrial sensor interfaces, audio preamplifiers, and discrete logic inverters requiring stable component supply across long-lifecycle embedded programs.

Supply support for 2N4125TA 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 2N4125TA belongs to Fairchild's legacy general-purpose bipolar transistor family, designed for cost-effective, reliable amplification and switching in non-automotive industrial and consumer electronics.

FAQ

What is the maximum collector-emitter voltage rating for the 2N4125TA?

The 2N4125TA has a maximum collector-emitter voltage (V_CEO) rating of 30 V under open-base conditions at T_A = 25 °C. This rating remains valid up to +125 °C ambient, but derating is required above 25 °C per the device's thermal characteristics. Exceeding 30 V risks irreversible breakdown and permanent damage to the 2N4125TA.

Does the 2N4125TA support linear amplification at audio frequencies?

Yes, the 2N4125TA supports linear amplification at audio frequencies, evidenced by its specified noise figure of 5.0 dB at 10 Hz–15.7 kHz and small-signal current gain (h_fe) of 50–200 across 1 kHz–100 MHz. Its low C_ob (4.5 pF) and stable h_FE make it suitable for microphone preamp and line-level gain stages when biased appropriately in the 2N4125TA's active region.

What is the typical base-emitter saturation voltage of the 2N4125TA?

The typical base-emitter saturation voltage (V_BE(sat)) of the 2N4125TA is 0.95 V when operated at I_C = 50 mA and I_B = 5.0 mA. This value is confirmed in the device's "ON CHARACTERISTICS" table and reflects the forward-biased PNP junction drop under hard saturation-critical for calculating base resistor values in switching applications using the 2N4125TA.

Can the 2N4125TA be used in high-frequency RF circuits?

No, the 2N4125TA is not intended for high-frequency RF circuits. Its small-signal current gain (h_fe) falls to 2.0 at 100 MHz, and its transition frequency (f_T) is not specified in the datasheet. The 2N4125TA is characterized for audio and low-speed switching applications up to ~10 MHz; for RF use, purpose-built RF transistors with documented f_T > 100 MHz should be selected instead of the 2N4125TA.

Is the 2N4125TA RoHS compliant and halogen-free?

The 2N4125TA was manufactured prior to full RoHS enforcement and is not certified RoHS compliant or halogen-free. Fairchild's documentation for this legacy part does not list Pb-free or green packaging options. For new designs requiring compliance, consult ON Semiconductor's modern PNP equivalents (e.g., NSS series) or verify material declarations directly with Aetrix Electronics' traceable lot data for the 2N4125TA.