onsemi BC238A

Overview

BC238A from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for low-noise amplification and general-purpose switching in analog and digital circuits, with hFE 120–220, V_CEO = 25 V, I_C = 100 mA, P_C = 500 mW, and f_T = 150 MHz (typ.) - used in audio preamplifiers, signal conditioning stages, and discrete logic interfaces.

For engineers reviewing the BC238A datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-92 package, DC current gain classification (A), collector-emitter saturation voltage (V_CE(sat) ≤ 0.2 V at I_C = 10 mA), noise figure (2 dB at 1 kHz), and thermal rating (T_J = 150°C).

Technical Context

The BC238A operates as a medium-speed, low-noise bipolar junction transistor optimized for linear amplification and saturated switching. Its hFE classification A (120–220) ensures predictable DC biasing stability, while f_T = 150 MHz (typ. at V_CE = 3 V, I_C = 0.5 mA) supports audio and low-RF signal handling. V_BE(on) = 0.55–0.7 V enables reliable turn-on with standard TTL-compatible drive levels.

Thermal design is supported by T_J = 150°C maximum junction temperature and T_STG = –55 to +150°C storage range. The device's Cob = 3.5–6 pF and Cib = 8 pF limit high-frequency parasitic coupling, making it suitable for stable small-signal gain stages without oscillation risk.

Key Specifications

Pinout & Package

BC238A is housed in a through-hole TO-92 plastic package (3.60 × 4.58 × 1.02 mm), with standardized lead spacing and mechanical robustness for manual and wave-solder assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC238A, BC546A offers higher voltage tolerance but no noise specification, while 2N3904 provides wider hFE spread and greater power margin but lacks documented low-noise performance - BC238A remains preferred where 2 dB NF and tight hFE control are design-critical.

Availability

BC238A is available at Aetrix Electronics and suitable for audio preamplifiers, discrete logic level shifters, and LED driver switches requiring stable component supply, consistent parametric binning, and long-lifecycle availability.

Supply support for BC238A 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 company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The BC238A belongs to Fairchild's BC237/238/239 family of general-purpose NPN transistors engineered for low-noise amplification and reliable switching in cost-sensitive consumer, industrial, and audio applications.

FAQ

What is the hFE range for BC238A?

The BC238A is binned to Class A, with a guaranteed DC current gain (hFE) range of 120 to 220 when measured at V_CE = 5 V and I_C = 2 mA. This tight hFE specification allows predictable biasing in amplifier and switching circuits without iterative trimming. The BC238A datasheet confirms this classification explicitly in the "hFE Classification" table and distinguishes it from BC238B (180–460) and BC238C (380–800). Designers should reference the BC238A specifically - not generic BC238 - to ensure compliance with this gain window.

Does BC238A have a specified noise figure?

Yes, the BC238A has a verified noise figure of 2 dB at 1 kHz, measured under V_CE = 5 V, I_C = 0.2 mA, and R_G = 2 kΩ. This value is shared with BC237 and confirmed in the "Noise Figure" section of the BC237/238/239 datasheet. It is lower than BC239's 4 dB (at 30–15 kHz), making BC238A particularly suitable for audio-band preamplification where low intrinsic noise is essential. The BC238A noise performance is a defined parameter - not estimated - and applies directly to the A-grade variant.

What is the maximum collector-emitter voltage for BC238A?

The BC238A has a maximum collector-emitter voltage (V_CEO) of 25 V, as specified in the Absolute Maximum Ratings table under "BC238/239". This rating applies under open-base conditions and must not be exceeded in circuit operation. It is lower than BC237's 45 V, reflecting the BC238A's optimization for lower-voltage, low-noise applications. Designers using BC238A must ensure that transient and steady-state V_CE remain within this 25 V limit to prevent avalanche breakdown or parametric shift.

Is BC238A suitable for switching applications?

Yes, BC238A is qualified for saturated switching with V_CE(sat) ≤ 0.2 V at I_C = 10 mA and I_B = 0.5 mA, and ≤ 0.6 V at I_C = 100 mA and I_B = 5 mA. Its fast turn-on/turn-off characteristics - supported by f_T = 150 MHz and low C_ob (3.5–6 pF) - enable reliable operation up to ~100 kHz in non-critical digital switching. While not optimized for high-speed power switching like RF transistors, BC238A delivers predictable, low-loss switching in LED drivers, relay drivers, and logic interface circuits.

What package type does BC238A use?

The BC238A uses the industry-standard TO-92 plastic package, with mechanical dimensions of 3.60 mm (length) × 4.58 mm (width) × 1.02 mm (thickness) and lead spacing matching JEDEC TO-92 specifications. Pinout is fixed as Emitter (1), Base (2), Collector (3) - confirmed in the "Package Dimensions" drawing and "Pin Identification" section of the datasheet. This package supports through-hole assembly and is compatible with legacy PCB footprints designed for BC546, 2N3904, and other TO-92 NPN transistors.