onsemi BC549B

Overview

BC549B from ON Semiconductor (formerly Fairchild) is an NPN epitaxial silicon transistor optimized for low-noise amplification and general-purpose switching in analog and signal-conditioning circuits. It features VCEO = 30 V, IC = 100 mA, hFE = 200–450 (Class B), fT = 300 MHz, and NF = 1.4–4.0 dB at 30–15 kHz, commonly deployed in audio preamplifiers, sensor interface stages, and low-power linear regulators.

For engineers reviewing the BC549B datasheet, pinout, applications, or equivalent options, key selection criteria include its low-noise performance, TO-92 package compatibility, DC current gain classification, saturation voltage behavior under 10 mA/0.5 mA drive, and suitability for discrete amplifier topologies requiring stable hFE across temperature.

Technical Context

The BC549B operates as a single-element NPN bipolar junction transistor with epitaxial base construction, enabling improved high-frequency response and reduced noise compared to diffused-base variants. Its design targets linear amplification where low input-referred noise and predictable hFE are critical - especially in microphone preamps and instrumentation front-ends.

It shares the same TO-92 3L package and pinout (Collector–Base–Emitter) with the BC546–BC550 family but is specifically binned for Class B hFE (200–450) and optimized for noise figure below 4.0 dB in the audio band. Unlike BC546/BC547, it does not support 65 V or 45 V VCEO ratings - its absolute maximum VCEO is 30 V, limiting use to sub-30 V rail applications.

Key Specifications

Pinout & Package

BC549B is housed in a JEDEC-standard TO-92 3-lead plastic package with straight leads (bulk or ammo/tape-and-reel variants). The case outline conforms to TO-92 dimensions per Figure 7 and Figure 8 of the original Fairchild datasheet Rev. 1.1.1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC549C and 2N3904, BC549B delivers the best compromise of verified low-noise operation (1.4–4.0 dB), predictable Class B hFE (200–450), and TO-92 compatibility - making it ideal for cost-sensitive, high-SNR analog signal chains operating below 30 V.

Availability

BC549B is available at Aetrix Electronics and suitable for audio preamplifiers, temperature sensor interfaces, and low-power LED drivers requiring stable component supply, long-term obsolescence management, and traceable sourcing.

Supply support for BC549B 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 (formerly Fairchild Semiconductor) is a global supplier of energy-efficient semiconductor solutions, specializing in power management, analog, sensors, and discrete devices for automotive, industrial, and consumer markets.

The BC549B belongs to ON Semiconductor's legacy general-purpose transistor product line, originally designed for cost-effective, high-reliability analog signal conditioning and switching in mass-produced electronic systems.

FAQ

What is the maximum collector-emitter voltage rating for BC549B?

The BC549B has an absolute maximum VCEO rating of 30 V, as specified in the Fairchild/ON Semiconductor datasheet Rev. 1.1.1. This value is strictly enforced - exceeding 30 V risks avalanche breakdown and permanent device failure. Designers must ensure all operating conditions, including transient spikes, remain within this limit. The BC549B is not rated for 45 V or 65 V rails like BC547 or BC546 variants.

How does BC549B differ from BC549C in practical circuit design?

The BC549B and BC549C share identical package, pinout, VCEO (30 V), and noise figure (1.4–4.0 dB), but differ in hFE binning: BC549B is Class B (200–450), while BC549C is Class C (420–800). In practice, BC549B provides more predictable gain control in feedback-based amplifiers, whereas BC549C suits ultra-low-base-current applications like high-impedance sensor buffers. BC549B remains preferred where gain stability outweighs maximum hFE.

Is BC549B suitable for RF amplifier applications?

Yes - the BC549B has a specified fT of 300 MHz and low Cob (3.5–6.0 pF), enabling use in VHF receiver front-ends, crystal oscillator buffers, and low-power RF detectors up to ~100 MHz. However, its noise figure is optimized for audio frequencies; for >10 MHz RF, verify impedance matching and stability with S-parameter models. BC549B is not characterized for UHF or microwave operation beyond 200 MHz.

What is the typical base-emitter on voltage (VBE(on)) for BC549B at 2 mA collector current?

The BC549B exhibits a typical VBE(on) of 660 mV at VCE = 5 V and IC = 2 mA, with a guaranteed range of 580–700 mV per the datasheet. This value is critical for calculating base resistor values in switch or amplifier bias networks. At higher currents (e.g., IC = 10 mA), VBE(on) rises to 720 mV - designers should reference the actual test condition when selecting operating points.

Does BC549B have a documented lead-free and RoHS-compliant version?

Yes - BC549B is manufactured by ON Semiconductor in RoHS-compliant, lead-free versions, as confirmed by official ON Semiconductor product change notices and packaging data. The TO-92 package uses matte tin plating on leads, and the device meets JEDEC J-STD-020 moisture sensitivity level (MSL) 1 requirements. No special handling or reflow profile deviations are needed for standard lead-free soldering processes.