onsemi MMBT3904LT3

Overview

MMBT3904LT3 from onsemi is a general-purpose NPN silicon transistor in SOT-23 package, rated for 40 V_CEO, 200 mA continuous collector current, and 300 MHz transition frequency (f_T). It delivers low V_CE(sat) (0.2 V at I_C = 10 mA, I_B = 1 mA) and high DC current gain (H_FE = 100–300 at I_C = 10 mA), commonly used in low-voltage switching and amplification circuits in consumer power supplies and signal conditioning stages.

For engineers reviewing the MMBT3904LT3 datasheet, pinout, applications, or equivalent options, key selection criteria include its SOT-23 footprint compatibility, guaranteed f_T ≥ 300 MHz, V_CE(sat) ≤ 0.3 V under 50 mA drive, RoHS-compliant Pb-free construction, and AEC-Q101 qualification for automotive-grade reliability validation.

Technical Context

This discrete NPN bipolar junction transistor operates in active, saturation, and cutoff regions with defined small-signal parameters: h_fe = 100–400 at 1 kHz, input impedance h_ie = 1–10 kΩ, output admittance h_oe = 1–40 μS, and noise figure ≤ 5.0 dB at 1 kHz with 100 μA collector bias.

Its thermal design supports 225 mW dissipation on FR-5 board (derated 1.8 mW/°C above 25°C) and 300 mW on alumina substrate (derated 2.4 mW/°C), with R_JA = 556 °C/W (FR-5) and 417 °C/W (alumina), enabling use in thermally constrained PCB layouts without forced cooling.

Key Specifications

Pinout & Package

SOT-23 (TO-236) surface-mount package: 2.90 mm × 1.30 mm × 1.00 mm body, 1.90 mm lead pitch, JEDEC-standard footprint compatible with automated placement and reflow.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN general-purpose transistor applications.

Compared with PN2222A and BC846B, the MMBT3904LT3 offers superior high-frequency performance (300 MHz vs. ≤250 MHz) and optimized SOT-23 thermal resistance (R_JA = 556 °C/W), making it preferred for compact, speed-critical switching and amplification where layout density and bandwidth are prioritized.

Availability

MMBT3904LT3 is available at Aetrix Electronics and suitable for LED driver circuits, microcontroller interface logic, DC-DC converter feedback networks, and audio pre-amplifier stages requiring stable component supply, consistent parametric performance, and long-term manufacturability.

Supply support for MMBT3904LT3 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensors, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The MMBT3904LT3 belongs to onsemi's general-purpose bipolar transistor product line, designed for cost-sensitive, high-volume applications demanding proven reliability, standardized packaging, and broad operating temperature support.

FAQ

What is the maximum junction temperature rating for the MMBT3904LT3?

The MMBT3904LT3 has a specified junction and storage temperature range of −55°C to +150°C. This allows operation in harsh environments such as automotive engine compartments or industrial motor drives. Thermal design must respect the 225 mW power dissipation limit on FR-5 board at 25°C ambient, derated linearly by 1.8 mW/°C above that point to avoid exceeding T_J(max). The MMBT3904LT3 maintains functional integrity across this full range when operated within its absolute maximum ratings.

Is the MMBT3904LT3 pin-compatible with other SOT-23 NPN transistors like the BC847?

The MMBT3904LT3 uses Style 6 pinout (Pin 1 = Base, Pin 2 = Emitter, Pin 3 = Collector), which matches BC847 variants marked with the same SOT-23 configuration. However, direct substitution requires verification of H_FE distribution, V_CE(sat), and f_T - BC847 typically offers higher gain but lower f_T (≈100 MHz). The MMBT3904LT3 is not guaranteed pin-compatible with BC847 variants using Style 7 (Emitter/Base/Collector) or other pinout variants. Always confirm marking diagram and mechanical drawing before replacement.

Does the MMBT3904LT3 support automotive applications?

Yes - the MMBT3904LT3 is AEC-Q101 qualified and PPAP capable, meeting stress-test requirements for automotive electronics including high-temperature operating life, temperature cycling, and electrostatic discharge. Its −55°C to +150°C operating range, Pb-free construction, and robust parametric stability make it suitable for cabin control modules, body electronics, and non-safety-critical ADAS subsystems. The MMBT3904LT3 is explicitly listed in onsemi's automotive-grade transistor portfolio.

What is the typical noise figure of the MMBT3904LT3 in small-signal amplifier configurations?

The MMBT3904LT3 has a maximum noise figure of 5.0 dB at V_CE = 5.0 V, I_C = 100 μA, R_S = 1.0 kΩ, and f = 1.0 kHz. At lower collector currents (e.g., 10–50 μA), NF improves to ~2–3 dB depending on source resistance - ideal for low-noise pre-amplifiers in sensor interfaces. This value is measured under standardized conditions and confirmed in the official onsemi datasheet; actual noise performance in a given MMBT3904LT3 circuit depends on biasing, layout, and external component selection.

Can the MMBT3904LT3 be used in linear (analog) amplifier applications?

Yes - the MMBT3904LT3 supports linear operation with verified small-signal parameters: h_fe = 100–400, h_ie = 1–10 kΩ, h_oe = 1–40 μS, and f_T ≥ 300 MHz. Its low distortion and stable gain across temperature make it suitable for Class-A audio pre-amplifiers, sensor signal conditioning, and feedback amplifiers. For best linearity, bias the MMBT3904LT3 at I_C = 0.1–10 mA with appropriate emitter degeneration and thermal stabilization.