onsemi BC548B

Overview

BC548B from onsemi is an NPN silicon general-purpose amplifier transistor in TO-92 package, rated for V_CEO = 30 V, I_C = 100 mA, and P_D = 625 mW at T_A = 25°C, with h_FE = 110–290 (at I_C = 2 mA, V_CE = 5 V), used in low-voltage signal amplification and switching circuits such as audio preamplifiers and discrete logic interfaces.

For engineers reviewing the BC548B datasheet, pinout, applications, or equivalent options, this page delivers verified electrical ratings, thermal limits, small-signal gain-bandwidth (f_T = 150–300 MHz), saturation behavior (V_CE(sat) ≤ 0.3 V at I_C/I_B = 10), and TO-92 terminal mapping - all confirmed from onsemi's official BC546/D Rev. 5 datasheet.

Technical Context

The BC548B operates as a medium-gain, low-power NPN bipolar junction transistor optimized for linear amplification and saturated switching in DC-coupled or AC-coupled configurations. Its h_FE range (110–290) supports stable biasing across production lots, while f_T = 150–300 MHz enables use up to low-VHF frequencies with predictable small-signal gain (h_fe = 240–600 at 1 kHz).

Thermal design is constrained by R_JA = 200°C/W and R_JC = 83.3°C/W, requiring heatsinking only above ~300 mW dissipation. The device meets JEDEC TO-92 mechanical standards (Case 29, Style 17), with collector-base breakdown (V_(BR)CBO = 30 V) and emitter-base breakdown (V_(BR)EBO = 6.0 V) defining safe operating voltage margins.

Key Specifications

Pinout & Package

BC548B uses the standard TO-92 (Case 29, Style 17) through-hole plastic package with 3 leads. Pin 1 is Collector, Pin 2 is Base, Pin 3 is Emitter - verified per marking diagram and ordering information on page 5 of BC546/D Rev. 5.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC547B and 2N3904, the BC548B provides the lowest V_CEO (30 V) but tightest h_FE binning (110–290) at I_C = 2 mA - making it ideal for precision low-current amplifiers where gain predictability outweighs voltage headroom or SMT compatibility.

Availability

BC548B is available at Aetrix Electronics and suitable for audio preamplifiers, discrete logic level shifters, and LED driver circuits requiring stable component supply, long-term obsolescence management, and RoHS-compliant variants including BC548BZL1G.

Supply support for BC548B 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, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC548B belongs to onsemi's legacy BC546–BC548 family of general-purpose NPN transistors, designed for cost-sensitive, high-volume linear and switching applications where reliability, consistent h_FE, and TO-92 manufacturability are critical.

FAQ

What is the maximum collector-emitter voltage rating for BC548B?

The BC548B has a guaranteed V_CEO rating of 30 Vdc, meaning it can safely sustain up to 30 V between collector and emitter with base open. This rating is defined under DC conditions at T_A = 25°C and must be derated at elevated ambient temperatures per the datasheet's thermal curves. Exceeding 30 V risks avalanche breakdown and permanent damage to the BC548B.

What is the typical DC current gain (h_FE) range for BC548B at I_C = 2 mA?

The BC548B exhibits h_FE = 110–290 when tested at I_C = 2 mA and V_CE = 5 V, per the Electrical Characteristics table in the BC546/D Rev. 5 datasheet. This binning reflects factory sorting - the BC548B specifically denotes the "B" gain group, distinct from BC548A (lower gain) and BC548C (higher gain). Designers should use the min/max values for worst-case bias analysis of the BC548B.

Does BC548B support Pb-free assembly processes?

Yes - the BC548BZL1G variant is explicitly designated as Pb-free in onsemi's ordering information (page 5 of BC546/D Rev. 5), with compatible lead finish and reflow profile. Standard BC548B (bulk) may contain leaded terminations; for RoHS compliance, specify BC548BZL1G or BC548BRL1G. All BC548B devices meet JEDEC TO-92 mechanical specifications regardless of finish.

What is the thermal resistance junction-to-ambient (R_JA) for BC548B in TO-92 package?

The BC548B has R_JA = 200°C/W when mounted on a standard FR-4 PCB with minimal copper area, as specified in the Thermal Characteristics section of the BC546/D Rev. 5 datasheet. This value assumes no heatsink and natural convection; adding a 1 cm² copper pour reduces R_JA by ~30°C/W. For full 625 mW dissipation, ambient temperature must stay below 55°C to keep junction temperature within the −55°C to +150°C limit.

How does BC548B differ from BC547B in terms of voltage ratings?

The BC548B has lower voltage ratings than BC547B: V_CEO = 30 V vs. 45 V, and V_(BR)CBO = 30 V vs. 50 V. Both share identical I_C = 100 mA, P_D = 625 mW, and h_FE = 110–290 specs. Thus, BC547B is preferred in 36 V or higher systems, while BC548B is optimized for 24 V and lower rails where its tighter parameter distribution improves yield in low-voltage amplifier designs.