onsemi BC549

Overview

BC549 from ON Semiconductor is a low-noise NPN epitaxial silicon transistor designed for small-signal amplification and switching in audio, RF, and precision analog circuits. It features VCEO = 30 V, IC = 100 mA, fT = 300 MHz, NF = 1.4–4.0 dB (30–15 kHz), and hFE range of 200–450 (B-grade) or 420–800 (C-grade), commonly used in microphone preamplifiers and oscillator stages.

For engineers reviewing the BC549 datasheet, pinout, applications, or equivalent options, this page delivers verified specifications, TO-92 pin configuration, low-noise design context, and validated alternative transistors for audio front-end and RF biasing use cases.

Technical Context

The BC549 operates as a general-purpose bipolar junction transistor with epitaxial base construction optimized for low noise across audio and low-VHF frequencies. Its noise figure is specified at VCE = 5 V, IC = 200 μA, RG = 2 kΩ, and f = 30–15,000 Hz - distinct from the broader 1 kHz test condition applied to BC546–BC548.

It shares the same TO-92 package and pinout as BC546–BC550 but differs in absolute maximum ratings: lower VCEO (30 V) and VEBO (5 V) versus BC546, and tighter hFE classification bands (B/C only). Complementary PNP types include BC559 and BC560.

Key Specifications

Pinout & Package

BC549 is housed in a JEDEC-standard TO-92 plastic package with straight leads (bulk) or formed leads (ammo/tape-and-reel). The device uses standard NPN lead assignment: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise NPN transistor applications.

Compared with BC549, BC550C offers higher guaranteed hFE and marginally better noise floor, while 2N5088 trades bandwidth for best-in-class 1 kHz noise performance - enabling selection based on frequency range and gain stability requirements.

Availability

BC549 is available at Aetrix Electronics and suitable for microphone preamplifiers, crystal oscillator buffers, and RF detector stages requiring stable component supply, long-term obsolescence management, and consistent parametric performance across production lots.

Supply support for BC549 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 logic solutions for automotive, industrial, and consumer markets.

The BC549 belongs to ON Semiconductor's legacy general-purpose transistor product line, originally developed by Fairchild and maintained for cost-sensitive, high-volume analog signal conditioning and switching applications.

FAQ

What is the maximum collector-emitter voltage rating for BC549?

The BC549 has a maximum collector-emitter voltage (VCEO) rating of 30 V at TA = 25°C. This value is confirmed in the Absolute Maximum Ratings table of the official BC546–BC550 datasheet. Exceeding this voltage risks avalanche breakdown and permanent device damage. Derating is required above 25°C ambient temperature per the datasheet's thermal curves. BC549 must not be substituted for BC546 (VCEO = 65 V) in high-voltage applications without circuit redesign.

Does BC549 have a specified noise figure, and under what conditions?

Yes, BC549 has a noise figure (NF) specification of 1.4–4.0 dB, measured at VCE = 5 V, IC = 200 μA, source resistance RG = 2 kΩ, and frequency range 30–15,000 Hz. This distinguishes it from BC546–BC548, which are rated at 1 kHz only. The BC549's broadband noise characterization makes it suitable for full-audio-range preamplifiers where consistent low-noise performance across 20 Hz–20 kHz is critical.

What package type and pin configuration does BC549 use?

BC549 is supplied exclusively in the TO-92 plastic package with three leads. Pin 1 is Collector, Pin 2 is Base, and Pin 3 is Emitter - verified across all ordering variants (e.g., BC549BTA, BC549BTF, BC549CTA). This pinout is standardized across the BC546–BC550 family and matches JEDEC TO-92 mechanical drawings. No alternate packages (SOT-23, SC-70) exist for BC549.

How does BC549 differ from BC547 in terms of key electrical parameters?

BC549 differs from BC547 in three key ways: (1) lower VCEO (30 V vs. 45 V), (2) lower VEBO (5 V vs. 6 V), and (3) dedicated low-noise optimization - BC549's NF is specified over 30–15 kHz, while BC547's is only rated at 1 kHz. BC549 also lacks the "A" hFE grade (110–220) offered in BC547, supporting only B (200–450) and C (420–800) grades. These differences make BC549 unsuitable as a direct replacement in higher-voltage or non-audio applications.

Is BC549 suitable for RF amplifier applications up to 100 MHz?

Yes, BC549 is suitable for RF amplifier applications up to approximately 100 MHz due to its 300 MHz current gain bandwidth product (fT) measured at IC = 10 mA and VCE = 5 V. Practical small-signal gain remains usable up to ~100 MHz in common-emitter configurations with proper biasing and impedance matching. However, its Cob (3.5–6.0 pF) and Cib (~9 pF) require careful layout to avoid instability - it is not recommended for VHF power amplification or broadband >150 MHz designs.