onsemi 2N3905_D29Z

Overview

2N3905_D29Z from Fairchild Semiconductor is a PNP bipolar junction transistor designed for general-purpose amplification and switching in low-power analog and digital circuits, with 40 V V_CEO, 200 mA I_C, and −55 °C to +150 °C operating temperature range; commonly used in signal inversion stages, discrete logic gates, and bias networks in industrial sensor interfaces.

For engineers reviewing the 2N3905_D29Z datasheet, pinout, applications, or equivalent options, key selection criteria include verified PNP polarity, TO-92 package compatibility, guaranteed h_FE ≥30 at 100 mA, saturation voltage ≤0.40 V under 50 mA/5 mA drive, and thermal resistance R_θJA = 200 °C/W for ambient-limited PCB layouts.

Technical Context

The 2N3905_D29Z operates as a standard junction-isolated PNP BJT with fixed emitter-base and collector-base junctions, supporting both linear amplification (via h_FE-controlled I_C/I_B ratio) and saturated switching (with V_CE(sat) ≤ 0.40 V at I_C = 50 mA). Its small-signal h_fe reaches 200 at 1 mA, and Cob = 4.5 pF enables stable operation up to ~100 MHz in common-emitter configurations.

Thermal design relies on its 625 mW total dissipation at 25 °C, derated by 5.0 mW/°C above ambient, and junction-to-ambient thermal resistance of 200 °C/W - requiring no heatsink below ~250 mW in still air. Noise figure is specified at 5.0 dB for 100 µA I_C, making it suitable for low-level audio preamplifier stages.

Key Specifications

Pinout & Package

2N3905_D29Z is housed in a through-hole TO-92 package (3-lead, epoxy-bodied, flat side facing viewer), with standardized lead orientation: Emitter (left), Base (center), Collector (right) when viewed with flat side toward user and leads pointing downward.

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 2N3905_D29Z provides the best balance of proven reliability, tight thermal spec (R_θJA = 200 °C/W), and broad h_FE applicability across 0.1–100 mA - ideal for cost-sensitive, medium-volume industrial controls where qualification history matters.

Availability

2N3905_D29Z is available at Aetrix Electronics and suitable for industrial sensor interfaces, discrete logic gates, and audio signal inversion requiring stable component supply, long-term obsolescence management, and traceable lot-level documentation.

Supply support for 2N3905_D29Z 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 2N3905_D29Z belongs to Fairchild's legacy general-purpose BJT family, engineered for robustness and consistency in industrial and commercial linear/switching applications where second-source availability and long-term manufacturability were critical.

FAQ

What is the maximum collector current rating for the 2N3905_D29Z?

The 2N3905_D29Z has a maximum continuous collector current (I_C) rating of 200 mA at T_A = 25 °C. Derating applies above this temperature - for example, at 85 °C ambient, usable I_C drops to approximately 170 mA to maintain junction temperature ≤150 °C. This rating supports typical relay drivers, LED switches, and preamp loads without forced cooling.

Is the 2N3905_D29Z pin-compatible with the 2N3904?

No - the 2N3905_D29Z is a PNP transistor while the 2N3904 is NPN, so their polarities are opposite. Though both use TO-92 packages with identical physical pinouts (E-B-C left-to-right), substituting one for the other without circuit revision will cause functional failure. The 2N3905_D29Z must be used in PNP-specific topologies such as high-side switches or inverting amplifiers with reversed supply connections.

What is the typical noise figure of the 2N3905_D29Z and under what conditions is it measured?

The 2N3905_D29Z has a specified noise figure 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 makes the 2N3905_D29Z suitable for low-level analog signal conditioning - for instance, amplifying thermocouple outputs or piezoelectric sensor signals where preserving signal integrity is essential.

Does the 2N3905_D29Z have a documented thermal resistance from junction to case (R_θJC)?

Yes - the 2N3905_D29Z has a documented R_θJC of 83.3 °C/W, measured under standard test conditions (T_A = 25 °C). This value is useful when estimating junction temperature rise under forced convection or when mounting to a heatsink via the collector tab (though TO-92 lacks a dedicated thermal pad, the metal leadframe offers limited conduction path).

Can the 2N3905_D29Z be used in switching applications above 10 MHz?

No - the 2N3905_D29Z is not optimized for RF switching. Its small-signal current gain (h_fe) falls to unity around 250 MHz, and Cob = 4.5 pF limits bandwidth in common-emitter configurations. For switching above 10 MHz, the 2N3905_D29Z is unsuitable; instead, consider RF-optimized transistors like the MMBT2907A or BFR92A, which specify f_T > 1 GHz and lower capacitance.