onsemi 2N3905TA

Overview

2N3905TA from ON Semiconductor (formerly Fairchild) is a PNP general-purpose bipolar junction transistor used for low-power amplification and switching in discrete 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 operates across –55°C to +150°C and supports applications such as signal inversion, LED drivers, and small-signal load switching.

For engineers reviewing the 2N3905TA datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, DC current gain range, saturation voltage performance at defined I_B/I_C conditions, thermal resistance (R_θJA = 200°C/W), and compatibility with through-hole PCB layouts using TO-92 footprints.

Technical Context

The 2N3905TA functions as a medium-speed, low-voltage PNP BJT optimized for linear amplification and saturated switching. Its h_fe = 50–200 at f = 1 kHz and I_C = 1–10 mA enables stable small-signal gain in audio preamps and sensor interfaces, while t_d/t_r/t_s/t_f ≤ 35/35/200/60 ns support reliable digital logic-level switching up to ~1 MHz.

It features V_(BR)CEO = 40 V and V_(BR)EBO = 5.0 V, defining safe operating limits for emitter-base reverse bias and collector-emitter breakdown. With C_ob = 4.5 pF and C_ib = 10 pF at specified test conditions, it maintains predictable high-frequency response in common-emitter configurations.

Key Specifications

Pinout & Package

2N3905TA is housed in a TO-92 plastic package with standard three-terminal configuration: Emitter (pin 1), Base (pin 2), Collector (pin 3), viewed from flat side with leads down and text upright.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 2N3905TA, MPSA56 offers higher voltage tolerance and broader h_FE, making it more robust in variable supply environments, while BC557 delivers superior small-signal gain at low currents but lacks the 200 mA continuous rating essential for power-switching roles.

Availability

2N3905TA is available at Aetrix Electronics and suitable for audio preamplifiers, LED driver circuits, discrete logic inverters, and level translation interfaces requiring stable component supply and long-term obsolescence management.

Supply support for 2N3905TA 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

ON Semiconductor is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, communications, computing, and consumer electronics.

The 2N3905TA belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, designed for cost-sensitive, reliability-critical discrete circuit building blocks in analog signal conditioning and digital interface applications.

FAQ

What is the maximum continuous collector current rating for the 2N3905TA?

The 2N3905TA has a maximum continuous collector current (I_C) rating of 200 mA at T_A = 25°C. This value decreases with rising ambient temperature per the derating curve (5.0 mW/°C above 25°C), and actual usable current must account for V_CE(sat) and thermal resistance to maintain junction temperature ≤ 150°C. The 2N3905TA datasheet specifies this limit under steady-state DC conditions.

Is the 2N3905TA pin-compatible with the 2N3904?

No, the 2N3905TA is not pin-compatible with the 2N3904 because they are complementary devices: 2N3905TA is PNP while 2N3904 is NPN. Although both use TO-92 packages with identical physical pinouts (Emitter–Base–Collector), their polarity reversal means direct substitution without circuit modification will cause functional failure. The 2N3905TA requires reversed biasing and load placement relative to the 2N3904.

What is the typical noise figure of the 2N3905TA and under what conditions is it measured?

The 2N3905TA has a typical noise figure (NF) of 5.0 dB, measured at V_CE = 5.0 V, I_C = 100 µA, source resistance R_S = 1.0 kΩ, and frequency bandwidth from 10 Hz to 15.7 kHz. This specification confirms its suitability for low-noise small-signal amplification tasks, and the 2N3905TA maintains this performance across the specified test conditions without requiring external noise-reduction components.

Does the 2N3905TA support pulsed operation beyond its DC ratings?

Yes, the 2N3905TA supports pulsed operation beyond its DC ratings, but only within limits defined in the datasheet's "Absolute Maximum Ratings" notes: pulse width ≤ 300 µs and duty cycle ≤ 2.0%. For such conditions, peak I_C may exceed 200 mA, but thermal and secondary breakdown constraints still apply. Engineers must consult ON Semiconductor's application guidance or perform transient thermal analysis before deploying the 2N3905TA in pulsed designs.

What is the base-emitter saturation voltage (V_BE(sat)) for the 2N3905TA at common operating points?

The 2N3905TA exhibits V_BE(sat) = 0.65 V at I_C = 10 mA / I_B = 1.0 mA and 0.85–0.95 V at I_C = 50 mA / I_B = 5.0 mA. These values define the minimum base drive voltage required to achieve full saturation and are critical for calculating base resistor values in switching applications. The 2N3905TA's V_BE(sat) remains stable across its rated temperature range.