onsemi BC550BU

Overview

BC550BU from ON Semiconductor is a low-noise NPN epitaxial silicon transistor optimized for small-signal amplification in audio and RF front-end stages, with VCEO = 45 V, hFE = 420–800 (Class C), fT = 300 MHz, and NF = 1.4–3.0 dB at 1 kHz. It operates in linear mode with IC ≤ 100 mA and PC = 500 mW in TO-92 packaging.

For engineers reviewing the BC550BU datasheet, pinout, applications, or equivalent options, key selection criteria include noise figure performance at low collector currents (200 µA), DC current gain linearity across 1–100 mA, saturation voltage under switching conditions, and compatibility with legacy BC-series bias networks in discrete amplifier designs.

Technical Context

The BC550BU belongs to the BC546–BC550 family of general-purpose NPN transistors designed for dual-role use in both linear amplification and digital switching. Its low-noise specification (NF ≤ 3.0 dB) and high fT (300 MHz) are validated at VCE = 5 V, IC = 200 µA and IC = 10 mA respectively - distinguishing it from BC546/BC547 variants with higher VCEO but higher noise.

It shares identical TO-92 3L package dimensions and pinout (Collector–Base–Emitter, pins 1–2–3) with BC546–BC549, enabling drop-in replacement where gain and noise requirements align. The hFE Class C bin (420–800) ensures predictable bias point stability in emitter-follower and common-emitter configurations with fixed-base resistors.

Key Specifications

Pinout & Package

BC550BU is housed in a JEDEC TO-92 3L molded plastic package with straight leads (bulk packing). Dimensions conform to standard TO-92 footprint (1.27 mm lead pitch, 4.7 mm body height), enabling compatibility with manual soldering and wave-solder processes.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN small-signal transistor applications.

Compared with BC550CTA, BC550BU offers identical performance in bulk packaging for lab use, while 2N5088 requires pinout adaptation and delivers marginally lower voltage headroom - making BC550BU preferable for legacy BC-series design continuity and rapid evaluation.

Availability

BC550BU is available at Aetrix Electronics and suitable for audio pre-amplifiers, RF intermediate frequency amplifiers, LED driver switches, and discrete logic level shifters requiring stable component supply across prototyping, low-volume production, and educational lab environments.

Supply support for BC550BU 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 manufacturer specializing in energy-efficient power management, analog, sensors, and connectivity solutions for automotive, industrial, and consumer markets.

The BC550BU belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, originally developed by Fairchild Semiconductor to provide standardized, low-cost, high-reliability discrete amplification and switching devices for broad analog design reuse.

FAQ

What is the pin configuration of BC550BU?

The BC550BU uses a standard TO-92 3L package with pinout: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter (viewed from flat side with leads down). This matches all BC546–BC550 variants and differs from complementary PNP types like BC560C, which follow E-B-C ordering. Always verify orientation using the flat-side marking before soldering.

Does BC550BU support audio-frequency amplification?

Yes, BC550BU is specifically characterized for low-noise audio applications, with NF = 1.4–3.0 dB measured at 1 kHz, VCE = 5 V, IC = 200 µA, and RG = 2 kΩ. Its hFE Class C (420–800) ensures consistent gain across the 20 Hz–20 kHz band when biased at IC = 1–10 mA, making it suitable for microphone preamps and line-level buffers.

How does BC550BU differ from BC547C?

BC550BU has lower noise (NF ≤ 3.0 dB vs. BC547C's 2.0–10.0 dB), same hFE Class C range (420–800), but reduced VCEO (45 V vs. 45 V for BC547C - identical), and identical fT (300 MHz). BC547C is optimized for general-purpose switching; BC550BU prioritizes signal integrity in analog gain stages where noise dominates performance.

Can BC550BU replace BC549B in an existing design?

BC550BU can replace BC549B in most cases, but verify operating point: BC549B has NF = 1.4–4.0 dB and hFE Class B (200–450), while BC550BU offers tighter hFE (420–800) and lower max NF (3.0 dB). If the original design relies on BC549B's lower gain or higher noise tolerance, minor bias resistor adjustment may be needed to maintain quiescent current.

What is the maximum power dissipation of BC550BU?

The BC550BU has a rated collector power dissipation (PC) of 500 mW at TA = 25°C in free air. Derating is required above 25°C - approximately 4.5 mW/°C - meaning usable power drops to ~300 mW at 70°C ambient. For sustained 100 mA operation, ensure junction temperature remains below 150°C via adequate copper area or airflow.