onsemi BCW33

Overview

BCW33 from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for low-power amplification and switching in compact circuits. It features a 32 V V_CEO, 500 mA I_C, DC current gain (h_FE) of 420–800 at 2 mA, and operates across –55 °C to +150 °C. It is commonly used in portable audio preamplifiers, LED driver stages, and signal conditioning circuits.

For engineers reviewing the BCW33 datasheet, pinout, applications, or equivalent options, key selection considerations include its SOT-23 package footprint, low V_CE(sat) of 0.25 V at 10 mA/0.5 mA drive, f_T of 200 MHz, and noise figure of 10 dB at 1 kHz - all critical for low-noise analog front-ends and high-speed switching.

Technical Context

The BCW33 is a silicon NPN planar epitaxial transistor optimized for general-purpose linear and switching operation up to 300 mA DC collector current. Its design emphasizes stable h_FE over temperature, low saturation voltage, and predictable small-signal behavior with f_T = 200 MHz and C_obo = 4.0 pF.

Thermal performance is defined for mounting on a 40 mm × 40 mm × 1.5 mm FR-4 PCB, delivering R_θJA = 357 °C/W and P_D = 350 mW at 25 °C, derating linearly at 2.8 mW/°C above ambient. Junction temperature must not exceed 150 °C under operation.

Key Specifications

Pinout & Package

BCW33 is housed in a surface-mount SOT-23 package (JEDEC TO-236AB), marked "D3", with standardized 1.90 mm × 1.30 mm footprint and 0.95 mm lead pitch. The device uses a 3-pin configuration: Pin 1 = Base, Pin 2 = Emitter, Pin 3 = Collector.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BCW33, BC847B offers higher voltage tolerance but reduced gain linearity, while MMBT3904 delivers better noise and bandwidth at the cost of lower h_FE - making BCW33 optimal for balanced gain, noise, and saturation performance in general-purpose analog stages.

Availability

BCW33 is available at Aetrix Electronics and suitable for audio pre-amplifier stages, LED constant-current drivers, signal level shifters, and low-speed digital interface buffers requiring stable component supply and long-term obsolescence management.

Supply support for BCW33 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

Fairchild Semiconductor was a U.S.-based semiconductor manufacturer specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The BCW33 belongs to Fairchild's general-purpose BJT family, engineered for cost-effective, reliable amplification and switching in consumer, industrial, and automotive auxiliary circuits.

FAQ

What is the maximum continuous collector current for BCW33?

The BCW33 supports a maximum DC collector current (I_C) of 500 mA, as specified in its Absolute Maximum Ratings. This rating assumes proper thermal management - specifically, mounting on a 40 mm × 40 mm × 1.5 mm FR-4 PCB. At ambient temperatures above 25 °C, power dissipation must be derated by 2.8 mW/°C to prevent exceeding the 150 °C maximum junction temperature. The BCW33 is typically operated at ≤300 mA for sustained reliability in general-purpose applications.

Does BCW33 have a documented pinout configuration, and what is it?

Yes, the BCW33 has a confirmed SOT-23 pinout: Pin 1 is Base, Pin 2 is Emitter, and Pin 3 is Collector - verified in the official Fairchild datasheet Rev. A (August 2002) and consistent across authorized distributor documentation. This arrangement matches JEDEC TO-236AB standard orientation, with the marking "D3" adjacent to Pin 1. No alternate pinouts or variants are documented for the BCW33; this configuration applies universally to all units supplied under this part number.

What is the typical noise figure of BCW33, and under what conditions is it measured?

The BCW33 has a typical noise figure (NF) of 10 dB, measured at I_C = 0.2 mA, V_CE = 5.0 V, R_S = 2.0 kΩ, f = 1.0 kHz, and BW = 200 Hz. This value reflects its suitability for low-level analog signal amplification, such as electret microphone pre-amplification or sensor signal conditioning. The BCW33's noise performance is competitive among general-purpose BJTs and is explicitly characterized in the "Small Signal Characteristics" section of its datasheet - not extrapolated or estimated.

Can BCW33 be used in switching applications, and what is its V_CE(sat)?

Yes, the BCW33 is qualified for switching use, with a typical collector-emitter saturation voltage (V_CE(sat)) of 0.25 V at I_C = 10 mA and I_B = 0.5 mA. This low saturation voltage reduces conduction losses and self-heating during on-state operation. Its f_T of 200 MHz and documented switching time curves (t_r, t_f, t_d, t_s) confirm usability in low-to-moderate speed digital and PWM-driven circuits - though it is not optimized for >1 MHz switching due to charge storage limitations inherent to its process.

What is the thermal resistance (R_θJA) of BCW33, and how does it affect PCB layout?

The BCW33 has a junction-to-ambient thermal resistance (R_θJA) of 357 °C/W when mounted on a standard 40 mm × 40 mm × 1.5 mm FR-4 PCB per JEDEC JESD51-3. This value implies that at 350 mW dissipation, the junction will rise ~125 °C above ambient - approaching its 150 °C limit. To maintain reliability, PCB layout should include ≥2 cm² of copper pour connected to the emitter pad (Pin 2), avoid enclosing the device under shields, and ensure airflow if ambient exceeds 50 °C. Derating is mandatory above 25 °C.