onsemi BC308ABU

Overview

BC308ABU from Fairchild Semiconductor is a PNP 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 = 180–460 (Class B), and TO-92 package. It operates in audio preamplifier stages and relay driver circuits where moderate gain and low leakage are required.

For engineers reviewing the BC308ABU datasheet, pinout, applications, or equivalent options, key selection criteria include its verified −25 V V_CEO, Class B h_FE range, −0.5 V typical V_CE(sat) at −10 mA/−0.5 mA, TO-92 mechanical compatibility, and documented noise figure of 2 dB at 1 kHz - all critical for discrete analog signal path design.

Technical Context

This PNP bipolar junction transistor uses epitaxial base construction to achieve stable DC current gain and low noise performance across audio frequencies. Its breakdown ratings (V_CES = −30 V, V_EBO = −5 V) and thermal limits (T_J = 150°C) support reliable operation in linear and saturated switching modes.

The device exhibits f_T = 130 MHz at V_CE = −5 V and I_C = −10 mA, with C_ob = 6 pF and C_ib = 12 pF at specified bias conditions - enabling use in RF-coupled preamp stages up to mid-VHF range when properly stabilized.

Key Specifications

Pinout & Package

BC308ABU is housed in a standard TO-92 plastic package with 3 leads, lead spacing 1.27 mm, body length 4.58 mm, and defined mechanical dimensions per Fairchild Rev. A2 specification.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC308ABU, BC327-25 offers higher voltage tolerance but looser h_FE control, while PN2907A trades noise and gain precision for broader ruggedness - making BC308ABU optimal for audio and precision analog switching where its 2 dB NF and Class B h_FE are decisive.

Availability

BC308ABU is available at Aetrix Electronics and suitable for audio preamplifiers, relay drivers, and LED constant-current sinks requiring stable component supply, long-lifecycle availability, and traceable sourcing.

Supply support for BC308ABU 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 analog, discrete, and power ICs before its acquisition by ON Semiconductor in 2016.

The BC307/308/309 series was developed as a family of general-purpose PNP transistors targeting audio, switching, and low-noise amplifier applications with standardized TO-92 packaging and binned h_FE.

FAQ

What is the maximum collector-emitter voltage rating for BC308ABU?

The BC308ABU has a guaranteed V_CEO rating of −25 V at T_A = 25°C, meaning it can safely withstand up to 25 volts reverse bias between collector and emitter in common-emitter configuration without breakdown. This value is confirmed in Fairchild's Rev. A2 datasheet under Absolute Maximum Ratings and Electrical Characteristics tables. Exceeding this voltage risks avalanche conduction and permanent damage to the BC308ABU.

Is BC308ABU suitable for low-noise audio amplifier designs?

Yes, BC308ABU is explicitly characterized for low-noise performance with a measured noise figure of 2 dB at 1 kHz (V_CE = −5 V, I_C = −0.2 mA, R_G = 2 kΩ), as documented in the Electrical Characteristics table. Its epitaxial structure and Class B h_FE binning further support stable, low-distortion operation in microphone preamp and line-level gain stages - making BC308ABU appropriate for high-fidelity analog signal chains.

What does the 'B' in BC308ABU signify?

The 'B' in BC308ABU denotes the h_FE gain classification bin: Class B corresponds to a DC current gain range of 180–460 at V_CE = −5 V and I_C = −2 mA. This binning ensures predictable biasing behavior across production units and is verified during final test. The full part number BC308ABU thus identifies the BC308 device, Class B gain group, and TO-92 package variant per Fairchild's ordering nomenclature.

Can BC308ABU replace BC307 or BC309 in a circuit?

BC308ABU is not a direct replacement for BC307 or BC309 due to differing electrical specifications: BC307 has V_CEO = −45 V and BC309 features lower noise (10 dB at 30–15 kHz) and higher h_FE (up to 800). Substituting BC308ABU for either may compromise voltage margin or noise performance. Always verify V_CEO, h_FE, and NF requirements before interchanging BC308ABU with BC307 or BC309 in an existing design.

What is the thermal resistance junction-to-ambient for BC308ABU?

While Fairchild's BC307/308/309 datasheet does not publish an explicit R_θJA value, the 500 mW power dissipation rating at T_A = 25°C implies a typical R_θJA of approximately 250°C/W for standard TO-92 mounting on non-thermal-pad PCBs. Derating is required above 25°C ambient - e.g., at 70°C ambient, maximum allowable P_C drops to ~300 mW. For precise thermal modeling, users should apply measured board-specific thermal resistance rather than assuming fixed R_θJA for BC308ABU.