onsemi 2N4400BU

Overview

2N4400BU from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for amplification and switching in low-to-medium power circuits, with V_CEO = 40 V, I_C = 600 mA continuous, h_FE = 20–150 at I_C = 1–500 mA, and TO-92 package. It serves in discrete amplifier stages, digital logic interface drivers, and relay/LED load switches in industrial control and consumer electronics.

For engineers reviewing the 2N4400BU datasheet, pinout, applications, or equivalent options, key selection criteria include its 40 V V_CEO, 600 mA I_C rating, TO-92 mechanical compatibility, saturation voltage performance under 0.75 V at 500 mA, and thermal resistance of 200 °C/W (R_θJA).

Technical Context

The 2N4400BU operates as a silicon NPN BJT with fixed-emitter configuration, optimized for linear amplification (h_fe = 2–250 at 1–20 mA, f = 100 MHz) and saturated switching (V_CE(sat) ≤ 0.75 V, V_BE(sat) ≤ 0.95 V at I_C = 500 mA). Its junction temperature range spans –55 °C to +150 °C, supporting operation in non-derated industrial ambient environments up to +70 °C.

Switching behavior is characterized by t_d = 15 ns, t_r = 20 ns, t_s = 225 ns, and t_f = 30 ns under V_CC = 30 V, I_C = 150 mA conditions. Small-signal parameters include C_ob = 6.5 pF and C_ib = 30 pF at specified bias points, enabling use in audio-frequency amplifiers and low-speed digital interfaces.

Key Specifications

Pinout & Package

2N4400BU is housed in a through-hole TO-92 package (JEDEC TO-92 variant), with standard lead configuration: Emitter (E), Base (B), Collector (C) arranged left-to-right when viewing the flat side with leads downward. The package supports manual soldering and socket insertion in prototyping and low-volume production.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN switching and amplification applications.

Compared with 2N2222A and MPS2222A, the 2N4400BU offers lower cost and proven stability in industrial temperature cycling, but has narrower h_FE range and longer storage time-making it optimal for cost-sensitive, moderate-speed switching rather than precision analog or high-frequency use.

Availability

2N4400BU is available at Aetrix Electronics and suitable for industrial control panels, consumer audio interfaces, and embedded sensor interface modules requiring stable component supply and long-term obsolescence management.

Supply support for 2N4400BU 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 2N4400BU belongs to Fairchild's general-purpose NPN transistor family, engineered for reliability in industrial-grade amplification and switching applications where cost, thermal robustness, and manufacturability are prioritized over ultra-high speed or ultra-low noise.

FAQ

What is the maximum collector-emitter voltage rating for the 2N4400BU?

The 2N4400BU has a maximum collector-emitter voltage (V_CEO) rating of 40 V. This value is measured with the base open and defines the absolute upper limit for voltage applied between collector and emitter before risk of avalanche breakdown. Operating above this rating-even briefly-may cause irreversible device failure. Designers should maintain at least 20 % derating margin (i.e., ≤32 V) in safety-critical or transient-prone applications.

Is the 2N4400BU suitable for switching a 500 mA load at 12 V?

Yes, the 2N4400BU supports 600 mA continuous collector current and 40 V V_CEO, making it suitable for switching a 500 mA, 12 V resistive or inductive load. At I_C = 500 mA and I_B = 50 mA, V_CE(sat) ≤ 0.75 V ensures <375 mW conduction loss. However, ensure adequate PCB copper area and ambient temperature ≤ 50 °C to avoid exceeding the 625 mW P_D limit at 25 °C.

Does the 2N4400BU have a documented transition frequency (f_T)?

No, the official Fairchild datasheet for the 2N4400BU does not specify transition frequency (f_T). While small-signal current gain h_fe is given as 2.0 at f = 100 MHz (I_C = 20 mA), this reflects degraded gain-not the unity-gain bandwidth. Therefore, the 2N4400BU is not characterized or recommended for RF amplification or high-speed digital switching above ~1 MHz.

What is the pin configuration of the 2N4400BU in TO-92 package?

The 2N4400BU uses 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 specification and is identical to 2N2222 and PN2222 devices, enabling mechanical and layout compatibility in most legacy designs.

Can the 2N4400BU replace a 2N3904 in existing circuit designs?

The 2N4400BU is not a direct replacement for the 2N3904 due to differences in current rating and gain: the 2N3904 is rated for I_C = 200 mA and h_FE = 100–300, while the 2N4400BU handles 600 mA but has h_FE = 20–150. Substitution may work in low-current switching roles if base drive is increased, but risks saturation failure or gain mismatch in linear amplifier stages. Always verify V_CE(sat), power dissipation, and h_FE requirements before substitution.