onsemi BC308

Overview

BC308 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 range of 120–800 (Class A/B/C), and TO-92 package. It operates in audio preamplifier stages and relay driver circuits where moderate gain and low saturation voltage are required.

For engineers reviewing the BC308 datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, −25 V V_CEO, −0.5 V typical V_CE(sat) at −10 mA/−0.5 mA, 130 MHz f_T, and classification-dependent h_FE spread - all critical for bias stability and small-signal linearity in discrete analog designs.

Technical Context

The BC308 is a junction-transistor device fabricated using epitaxial base technology to achieve consistent DC current gain and low noise performance across h_FE classes (A: 120–220, B: 180–460, C: 380–800). Its structure supports stable operation up to 150°C junction temperature and exhibits Cob = 6 pF and Cib = 12 pF at specified test conditions.

It functions as a linear amplifying element or saturated switch, with V_BE(on) = −0.55 to −0.7 V and V_BE(sat) = −0.7 to −0.85 V depending on drive level. The device is not optimized for RF power but delivers usable bandwidth up to 130 MHz under small-signal conditions (V_CE = −5 V, I_C = −10 mA).

Key Specifications

Pinout & Package

BC308 is housed in a standard TO-92 plastic package with 3 leads, compatible with through-hole PCB assembly and manual prototyping. Lead spacing and outline conform to JEDEC TO-92 specifications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC327 and 2N3906, the BC308 offers superior noise performance and graded h_FE bins for analog matching, while trading off maximum voltage and current capability - making it ideal for mid-performance audio and precision biasing where parameter consistency matters more than raw ratings.

Availability

BC308 is available at Aetrix Electronics and suitable for audio preamplifier stages, relay driver circuits, and LED current sink applications requiring stable component supply, long-term obsolescence management, and traceable sourcing.

Supply support for BC308 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 BC307/308/309 family was developed for general-purpose linear amplification and switching in consumer, industrial, and instrumentation equipment where reliability, gain consistency, and low-noise operation were prioritized over ultra-high speed or power density.

FAQ

What is the maximum collector-emitter voltage rating for BC308?

The BC308 has a maximum collector-emitter voltage (V_CEO) rating of −25 V at T_A = 25°C. This value is confirmed in the Absolute Maximum Ratings table of the Fairchild BC307/308/309 datasheet Rev. A2. Exceeding this voltage risks avalanche breakdown and permanent device failure. Derating is required at elevated temperatures per the datasheet's thermal curves.

Does BC308 have multiple hFE gain classifications, and how do they differ?

Yes, the BC308 is offered in three h_FE classifications: Class A (120–220), Class B (180–460), and Class C (380–800), all tested at V_CE = −5 V and I_C = −2 mA. These bins enable selective matching for differential pairs or consistent gain in production batches. The BC308 part number itself does not indicate classification - it must be verified via date code or packaging marking per Fairchild's labeling convention.

What is the noise figure of BC308, and under what conditions is it specified?

The BC308 has a noise figure (NF) of 2 dB, measured at V_CE = −5 V, I_C = −0.2 mA, R_G = 2 kΩ, and f = 1 kHz. This specification applies to BC307 and BC308 variants only; BC309 has a higher 4 dB NF at 30–15 kHz. The low NF makes BC308 suitable for first-stage amplification in low-level analog signal chains where noise contribution must be minimized.

Is BC308 pin-compatible with BC327 or 2N3906?

Yes, BC308 is pin-compatible with both BC327 and 2N3906 in the TO-92 package: Collector (pin 1), Base (pin 2), Emitter (pin 3). However, electrical differences - including V_CEO, I_C, h_FE range, and noise figure - require circuit validation before substitution. The BC308 datasheet confirms identical pinout mapping across the BC307/308/309 series.

What is the typical collector-emitter saturation voltage for BC308?

The typical collector-emitter saturation voltage (V_CE(sat)) for BC308 is −0.5 V at I_C = −10 mA and I_B = −0.5 mA, and −0.3 V at I_C = −100 mA and I_B = −5 mA. These values are specified in the Electrical Characteristics table of the Fairchild BC307/308/309 datasheet and reflect low conduction loss essential for efficient switching in relay and LED driver applications.