onsemi BC546BU

Overview

BC546BU from ON Semiconductor is a general-purpose NPN epitaxial silicon transistor in TO-92 package, rated for 65 V V_CEO, 100 mA I_C, and 500 mW P_C, commonly used in low-power switching and linear amplification circuits such as signal buffering in audio preamps and sensor interface stages.

For engineers reviewing the BC546BU datasheet, pinout, applications, or equivalent options, key selection considerations include its h_FE classification (A/B/C variants), V_CEO rating relative to supply rails, saturation voltage at defined I_B/I_C conditions, noise figure in low-level amplification, and TO-92 mechanical compatibility with manual prototyping and through-hole production.

Technical Context

The BC546BU belongs to the BC546–BC550 family of discrete NPN transistors optimized for cost-sensitive, medium-speed analog and digital applications. It features a planar epitaxial base structure enabling stable h_FE across temperature and consistent V_BE(on) of 580–700 mV at I_C = 2 mA.

Its 300 MHz f_T supports operation up to mid-audio frequencies, while Cob ≤ 6.0 pF and Cib ≈ 9 pF minimize capacitive loading in high-impedance node interfaces. The device operates reliably from –65°C to +150°C junction temperature with no derating required below 25°C ambient.

Key Specifications

Pinout & Package

BC546BU is housed in a JEDEC TO-92 3-lead plastic package with straight leads (bulk packing). Pin 1 is Collector, Pin 2 is Base, Pin 3 is Emitter - verified per Fairchild/ON Semiconductor physical dimensions diagrams and ordering information tables.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC547BU and 2N3904, BC546BU provides the highest V_CEO rating in the family, making it the only choice among these three for reliable operation in 48 V systems or transient-prone industrial environments without additional clamping.

Availability

BC546BU is available at Aetrix Electronics and suitable for audio signal conditioning, sensor interface circuits, relay driver stages, and logic-level translation requiring stable component supply across prototyping, pilot production, and long-lifecycle industrial programs.

Supply support for BC546BU 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, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC546BU belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, originally developed by Fairchild and maintained for broad compatibility in cost-sensitive, through-hole-based analog and mixed-signal designs.

FAQ

What is the maximum collector-emitter voltage rating for BC546BU?

The BC546BU has a V_CEO rating of 65 V, meaning it can safely block up to 65 volts between collector and emitter when the base is open. This value is confirmed in the Absolute Maximum Ratings table of the official ON Semiconductor datasheet for BC546/BC547/BC548/BC549/BC550. Exceeding this voltage risks avalanche breakdown and permanent damage to the BC546BU.

Does BC546BU have a specified noise figure, and under what conditions?

Yes, the BC546BU has a noise figure (NF) of 2.0–10.0 dB, measured at V_CE = 5 V, I_C = 200 μA, f = 1 kHz, and R_G = 2 kΩ. This specification applies to the BC546/BC547/BC548 variants and is documented in the Electrical Characteristics section of the datasheet. The BC546BU's NF performance makes it suitable for low-noise preamplifier stages where signal integrity is critical.

What are the h_FE classification ranges for BC546BU, and how do they affect circuit design?

The BC546BU is available in A, B, and C h_FE grades: A = 110–220, B = 200–450, C = 420–800. These classifications are measured at V_CE = 5 V and I_C = 2 mA. Designers select grade based on required bias stability - e.g., C-grade enables lower base drive current in switching applications, while A-grade offers tighter gain tolerance in matched-pair amplifiers using BC546BU.

Is BC546BU pin-compatible with BC547BU or 2N3904?

Yes, BC546BU shares the same TO-92 package and pinout (Collector-Base-Emitter on pins 1-2-3) with BC547BU and 2N3904. However, it is not a drop-in replacement in all cases due to differences in V_CEO (65 V vs. 45 V vs. 40 V) and h_FE distribution. System validation is required when substituting BC546BU for either part, especially in high-voltage or precision-gain applications.

What is the typical current gain-bandwidth product (f_T) of BC546BU, and what does it imply for signal frequency response?

The BC546BU has an f_T of 300 MHz, measured at V_CE = 5 V, I_C = 10 mA, and f = 100 MHz. This indicates the frequency at which current gain drops to unity, supporting usable amplification up to several tens of MHz in optimized common-emitter configurations. In practice, BC546BU delivers clean audio band amplification (<20 kHz) and reliable digital signal conditioning up to ~10 MHz, limited more by layout and bias than intrinsic device bandwidth.