onsemi 2N3905BU

Overview

2N3905BU from Fairchild Semiconductor is a PNP bipolar junction transistor designed for general-purpose amplification and switching in low-power analog and digital circuits, with V_CEO = 40 V, I_C = 200 mA continuous, h_FE = 30–150 (at I_C = 0.1–100 mA), and TO-92 package. It serves as an active switch or small-signal amplifier in discrete logic interfaces, sensor biasing, and LED drivers.

For engineers reviewing the 2N3905BU datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, 40 V breakdown rating, 200 mA collector current capability, thermal resistance (R_θJA = 200 °C/W), and verified performance across –55 °C to +150 °C junction temperature range.

Technical Context

The 2N3905BU operates as a silicon PNP BJT with fixed-emitter bias topology, supporting both linear amplification (V_CE ≥ 1 V, h_FE-dependent gain) and saturated switching (V_CE(sat) ≤ 0.40 V at I_C = 50 mA). Its DC current gain varies significantly with collector current-30 at 100 mA, 50 at 10 mA, and up to 150 at 0.1 mA-enabling design flexibility across operating points.

Small-signal parameters include h_fe = 50–200 (f = 1 kHz), C_ob = 4.5 pF, C_ib = 10 pF, and NF = 5.0 dB (at 100 µA, 10 Hz–15.7 kHz), confirming suitability for audio-frequency amplification and low-noise preamplifier stages where bandwidth and noise floor matter.

Key Specifications

Pinout & Package

2N3905BU is housed in a through-hole TO-92 package (3-lead, epoxy-bodied, standard outline per JEDEC TO-92). Lead identification follows EIAJ SC-43 standard: flat side facing viewer, leads down, left-to-right = Emitter (E), Base (B), Collector (C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA56 and BC557, the 2N3905BU offers tighter h_FE consistency at mid-currents (50 at 10 mA), lower cost in high-volume production, and proven thermal stability over –55 °C to +150 °C-making it optimal for cost-sensitive industrial controls where predictable gain and ruggedness outweigh extreme parameter ranges.

Availability

2N3905BU is available at Aetrix Electronics and suitable for industrial control panels, audio signal conditioning circuits, and discrete logic interface modules requiring stable component supply and long-term manufacturability.

Supply support for 2N3905BU 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 2N3905BU belongs to Fairchild's legacy general-purpose bipolar transistor family, engineered for reliability and consistency in cost-sensitive, medium-speed amplification and switching applications across consumer, industrial, and computing markets.

FAQ

What is the maximum collector-emitter voltage rating for the 2N3905BU?

The 2N3905BU has a maximum collector-emitter voltage (V_CEO) rating of 40 V at T_A = 25 °C. This rating is based on a maximum junction temperature of 150 °C and must be derated at elevated ambient temperatures per the device's thermal characteristics. Exceeding this voltage risks irreversible breakdown and permanent damage to the 2N3905BU.

Does the 2N3905BU support operation at elevated temperatures?

Yes, the 2N3905BU is rated for junction temperatures from –55 °C to +150 °C. Its thermal resistance (R_θJA = 200 °C/W) and power dissipation curve confirm stable operation across this full range when mounted on standard PCBs without forced airflow. The 2N3905BU maintains specified h_FE and V_CE(sat) performance within these limits.

What is the typical DC current gain (h_FE) of the 2N3905BU at 10 mA collector current?

At V_CE = 1.0 V and I_C = 10 mA, the 2N3905BU exhibits a typical DC current gain (h_FE) of 50, with a guaranteed minimum of 30 and maximum of 150 across production lots. This value is confirmed in the device's official electrical characteristics table and reflects its behavior in linear amplification and partially saturated switching modes.

Can the 2N3905BU be used as a direct replacement for the 2N3906 in circuit designs?

No-the 2N3905BU is not a direct replacement for the 2N3906. Although both are PNP transistors in TO-92 packages, the 2N3906 has V_CEO = 40 V and h_FE = 100–300, while the 2N3905BU has h_FE = 30–150 and slightly different saturation characteristics. Circuit validation is required before substituting the 2N3905BU in a design originally using the 2N3906.

What is the noise figure specification for the 2N3905BU and under what conditions is it measured?

The 2N3905BU has a noise figure (NF) of 5.0 dB, measured at V_CE = 5.0 V, I_C = 100 µA, R_S = 1.0 kΩ, and bandwidth from 10 Hz to 15.7 kHz. This specification confirms its suitability for low-noise preamplifier applications, and the value is explicitly listed in the "Small Signal Characteristics" section of the official 2N3905BU datasheet.