onsemi 2N4126TA

Overview

2N4126TA from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor (BJT) designed for low-to-medium current amplification and switching applications, with confirmed V_CEO = 25 V, I_C = 200 mA continuous, and h_FE = 120–360 at I_C = 2.0 mA. It operates across –55°C to +150°C and is commonly used in discrete amplifier stages, level-shifting circuits, and low-power logic interface switches.

For engineers reviewing the 2N4126TA datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, TO-92 package mechanical compatibility, DC current gain linearity at 2–50 mA, saturation voltage under β = 10 drive, and thermal resistance (R_θJA = 200°C/W on FR-4).

Technical Context

The 2N4126TA implements a silicon planar epitaxial PNP BJT structure optimized for stable h_FE over temperature and low noise figure (NF = 4.0 dB at 10 Hz–15.7 kHz). Its f_T = 250 MHz enables use in audio-frequency amplifiers and fast-switching digital interfaces up to ~10 MHz.

It features symmetrical breakdown ratings: V_(BR)CEO = V_(BR)CBO = 25 V and V_(BR)EBO = 4.0 V, with cutoff currents ICBO ≤ 50 nA and IEBO ≤ 50 nA - confirming suitability for high-impedance bias networks and battery-powered standby circuits.

Key Specifications

Pinout & Package

2N4126TA is housed in a through-hole TO-92 package (JEDEC TO-92 variant), with standardized lead configuration: Emitter (lead 1), Base (lead 2), Collector (lead 3), flat side facing viewer, leads downward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT4126, 2N4126TA offers identical electrical behavior but requires through-hole assembly and delivers lower thermal resistance (200 vs. 357°C/W); versus 2N3906, it provides higher minimum h_FE and tighter gain distribution - critical for production-stable amplifier biasing.

Availability

2N4126TA is available at Aetrix Electronics and suitable for audio signal conditioning, industrial relay control, logic level translation, and discrete analog circuit design requiring stable component supply and long-term manufacturability.

Supply support for 2N4126TA 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 (now part of ON Semiconductor) is a historically significant analog and discrete semiconductor manufacturer known for high-reliability bipolar transistors and power devices.

The 2N4126TA belongs to Fairchild's legacy general-purpose PNP BJT product line, engineered for broad utility in linear amplification, switching, and interface functions across consumer, industrial, and automotive auxiliary systems.

FAQ

What is the maximum continuous collector current rating for the 2N4126TA?

The 2N4126TA has a maximum continuous collector current (I_C) rating of 200 mA at T_A = 25°C. This value is derated above 25°C per the specified thermal resistance (R_θJA = 200°C/W), and operation beyond this limit risks thermal runaway or permanent degradation. Always verify actual board-level dissipation using V_CE × I_C and ambient conditions before finalizing the 2N4126TA design-in.

Does the 2N4126TA support audio-frequency amplification?

Yes, the 2N4126TA supports audio-frequency amplification with verified performance: f_T = 250 MHz ensures ample gain-bandwidth margin, NF = 4.0 dB at 100 µA confirms low-noise capability, and h_FE stability across –40°C to 125°C enables consistent biasing. Its PNP topology is especially effective in single-supply preamp topologies where emitter-follower buffering or common-emitter gain stages are required - all validated in the 2N4126TA datasheet's typical characteristics plots.

What is the pin configuration of the 2N4126TA in TO-92 package?

The 2N4126TA uses the standard TO-92 pinout: when viewing the flat side of the package with leads pointing downward, the left-to-right pin order is Emitter (E), Base (B), Collector (C). This matches JEDEC TO-92 configuration and is explicitly shown in the 2N4126TA datasheet's mechanical drawings. Correct orientation is essential to avoid reverse-bias damage or circuit malfunction during prototyping or production assembly of the 2N4126TA.

How does the 2N4126TA compare to the MMBT4126 in terms of thermal performance?

The 2N4126TA exhibits superior thermal performance compared to the MMBT4126: its R_θJA is 200°C/W on FR-4, whereas the MMBT4126's R_θJA is 357°C/W. This 157°C/W difference means the 2N4126TA can dissipate more power at the same ambient temperature or operate at lower junction temperatures under identical load conditions. That advantage stems directly from the TO-92 package's larger copper leadframe and thermal mass - a key differentiator when selecting between 2N4126TA and MMBT4126 for thermally demanding applications.

Is the 2N4126TA suitable for switching applications at 100 kHz?

Yes, the 2N4126TA is suitable for switching applications up to at least 100 kHz. Its f_T = 250 MHz and documented switching times (t_on, t_off, t_r, t_f) in the datasheet show sub-100 ns transitions at I_C = 10–50 mA, supporting clean square-wave generation and efficient duty-cycle control. For reliable 100 kHz operation, ensure base drive strength achieves β ≈ 10–20, maintain V_CE within 25 V, and verify layout minimizes parasitic inductance - all validated in the 2N4126TA's switching characteristics graphs.