onsemi BC308A

Overview

BC308A 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 reliable saturation are required.

For engineers reviewing the BC308A datasheet, pinout, applications, or equivalent options, key selection criteria include its −25 V V_CEO, Class B h_FE range, low V_CE(sat) of −0.5 V at −10 mA/−0.5 mA, noise figure of 2 dB at 1 kHz, and TO-92 mechanical compatibility across BC307/308/309 family variants.

Technical Context

The BC308A is a discrete PNP bipolar junction transistor optimized for linear amplification and saturated switching in low-to-medium power analog and digital circuits. Its h_FE classification (B: 180–460) ensures predictable DC current gain under V_CE = −5 V and I_C = −2 mA conditions, while f_T = 130 MHz supports audio-frequency signal handling.

It features low base-emitter on voltage (V_BE(on) = −0.55 to −0.7 V), tight saturation characteristics (V_CE(sat) = −0.5 V @ −10 mA/−0.5 mA), and low output capacitance (C_ob = 6 pF @ V_CB = −10 V), enabling stable operation in high-input-impedance amplifier nodes and fast-switching logic interfaces.

Key Specifications

Pinout & Package

BC308A is housed in a standard TO-92 plastic package with 3 leads, compatible with through-hole PCB assembly and manual prototyping. Lead spacing and body dimensions conform to JEDEC TO-92 outline (3.60 ±0.20 mm width, 4.58 +0.25/−0.15 mm height).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC308A, BC327-40 offers higher voltage tolerance but broader h_FE variation, while PN2907A trades gain precision for robustness-making BC308A optimal for cost-sensitive, noise-critical 12 V–24 V analog and switching designs where −25 V rating suffices.

Availability

BC308A is available at Aetrix Electronics and suitable for audio preamplifiers, relay driver modules, and LED current sink circuits requiring stable component supply, long-lifecycle availability, and TO-92 through-hole compatibility.

Supply support for BC308A 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 series was developed as a family of general-purpose PNP transistors targeting cost-effective, reliable amplification and switching in consumer, industrial, and automotive auxiliary circuits.

FAQ

What is the maximum collector-emitter voltage rating for BC308A?

The BC308A 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 BC307/308/309 datasheet Rev. A2. Exceeding this voltage risks avalanche breakdown. The BC308A also specifies V_CES = −30 V for collector-emitter with base shorted to emitter-a condition sometimes used in switching layouts.

Is BC308A suitable for low-noise audio amplifier applications?

Yes, BC308A is suitable for low-noise audio amplifier applications, with a specified noise figure of 2 dB at 1 kHz (V_CE = −5 V, I_C = −0.2 mA, R_G = 2 kΩ). This performance is documented in the Electrical Characteristics section of the BC307/308/309 datasheet. While BC309 offers lower noise (10 dB at 30–15 kHz), BC308A's 2 dB figure makes it appropriate for microphone preamps and line-level stages where wideband noise is less critical than 1 kHz dominance.

What h_FE classification does BC308A belong to, and how is it verified?

BC308A belongs to h_FE Class B, with a guaranteed DC current gain range of 180–460 at V_CE = −5 V and I_C = −2 mA. This classification is explicitly defined in the "Classification" table of the Fairchild BC307/308/309 datasheet Rev. A2. Units marked "BC308A" are binned during final test to meet this gain window, ensuring consistency across production lots for bias-critical amplifier designs.

Does BC308A have the same pinout as BC307 and BC309?

Yes, BC308A shares the identical TO-92 pinout with BC307 and BC309: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter. This is confirmed in the "BC307/308/309" header and pin diagram on page 1 of the Fairchild datasheet Rev. A2. The mechanical drawing and labeling apply uniformly across the family, enabling direct substitution in existing PCB layouts without rework-provided voltage and gain requirements align.

What is the typical saturation voltage of BC308A under standard switching conditions?

The typical V_CE(sat) of BC308A is −0.5 V when operated at I_C = −10 mA and I_B = −0.5 mA, as specified in the Electrical Characteristics table. This low saturation voltage ensures minimal power loss and reliable turn-on in digital switching applications such as relay drivers and LED sinks. At higher currents (I_C = −100 mA, I_B = −5 mA), V_CE(sat) drops further to −0.3 V, confirming strong saturation capability.