onsemi BC238ATFR

Overview

BC238ATFR from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for low-noise amplifier and general-purpose switching applications, with V_CEO = 25 V, I_C = 100 mA, P_C = 500 mW, h_FE = 120–800 (Class A/B/C), and f_T = 85–250 MHz - used in audio preamplifiers, signal conditioning stages, and discrete logic interface circuits.

For engineers reviewing the BC238ATFR datasheet, pinout, applications, or equivalent options, key selection criteria include DC current gain classification, saturation voltage at defined drive conditions, noise figure in low-current biasing, TO-92 thermal derating behavior, and safe operating area limits under pulsed vs. DC loads.

Technical Context

The BC238ATFR operates as a medium-speed, low-noise bipolar junction transistor optimized for linear amplification and soft-switching roles in analog front-ends and discrete logic translators. Its h_FE classification (A/B/C) defines gain binning at V_CE = 5 V, I_C = 2 mA, while f_T varies from 85 MHz (I_C = 10 mA) to 250 MHz (I_C = 0.5 mA), indicating frequency-dependent gain roll-off.

Noise performance is specified only for BC237/238 variants (NF = 2 dB at V_CE = 5 V, I_C = 0.2 mA, f = 1 kHz, R_G = 2 kΩ), distinguishing it from BC239's higher-noise profile. Saturation parameters (V_CE(sat), V_BE(sat)) are validated at two drive levels (I_C/I_B = 10/0.5 mA and 100/5 mA), supporting both small-signal and moderate-power switching design.

Key Specifications

Pinout & Package

BC238ATFR is housed in a standard TO-92 plastic package (3.60 mm × 4.58 mm × 4.58 mm max), with lead spacing of 1.27 mm and thermal resistance θ_JA ≈ 200°C/W (typical, free-air).

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, BC238ATFR offers verified low-noise performance at 1 kHz and broader h_FE binning - making it preferred for precision analog front-ends where gain consistency and SNR outweigh raw speed or voltage headroom.

Availability

BC238ATFR is available at Aetrix Electronics and suitable for audio preamplifiers, discrete logic level shifters, low-power LED drivers, and analog signal conditioning circuits requiring stable component supply and long-term obsolescence management.

Supply support for BC238ATFR 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 BC238ATFR belongs to Fairchild's legacy BC237/238/239 family of general-purpose NPN transistors, engineered for reliable low-noise amplification and robust switching in consumer, industrial, and communication equipment.

FAQ

What is the maximum collector-emitter voltage rating for BC238ATFR?

The BC238ATFR has a V_CEO rating of 25 V, meaning it can safely withstand up to 25 volts between collector and emitter with the base open. This value is confirmed in the Absolute Maximum Ratings table of the Fairchild BC237/238/239 datasheet Rev. A2. Exceeding this voltage risks avalanche breakdown and permanent device failure. Always apply appropriate derating for temperature and reliability margins when using BC238ATFR in production designs.

Does BC238ATFR have a specified noise figure, and under what conditions?

Yes, BC238ATFR has a noise figure of 2 dB, measured at V_CE = 5 V, I_C = 0.2 mA, f = 1 kHz, and R_G = 2 kΩ - explicitly stated for BC237/238 variants in the Electrical Characteristics table. This makes BC238ATFR suitable for low-noise preamplifier stages where signal integrity is critical. The BC239 variant has higher noise (10 dB), so BC238ATFR is the preferred choice when low-noise performance is required.

What h_FE classification does BC238ATFR carry, and how is it marked?

BC238ATFR is a Class A/B/C h_FE transistor, with gain ranges of 120–220 (A), 180–460 (B), and 380–800 (C). The "TFR" suffix denotes tape-and-reel packaging and does not indicate gain bin; actual h_FE is marked on the device body per Fairchild's standard coding (e.g., "A", "B", or "C"). Datasheet Table "hFE Classification" confirms these bins apply to BC238, and BC238ATFR inherits them fully.

Is BC238ATFR pin-compatible with other TO-92 NPN transistors like 2N3904?

Yes, BC238ATFR uses the standard TO-92 package with pinout 1 = Emitter, 2 = Base, 3 = Collector - identical to 2N3904, BC547, and PN2222. Mechanical compatibility is confirmed by Fairchild's Package Dimensions drawing showing 1.27 mm lead pitch and 3.60 mm body width. However, electrical differences (e.g., V_CEO, h_FE, NF) require circuit validation before substitution, even though BC238ATFR fits the same footprint.

What is the typical f_T of BC238ATFR, and how does it vary with operating conditions?

The BC238ATFR exhibits f_T = 85 MHz at V_CE = 5 V, I_C = 10 mA and f_T = 250 MHz at V_CE = 3 V, I_C = 0.5 mA, as shown in the Electrical Characteristics table. This strong current dependence means f_T drops significantly at higher collector currents - a key consideration when designing RF amplifiers or high-speed switches. Designers must consult the Typical Characteristics Figure 6 to model f_T vs. I_C for BC238ATFR in their specific bias point.