onsemi BC558B

Overview

BC558B from onsemi is a PNP epitaxial silicon transistor designed for general-purpose switching and linear amplification in low-to-medium power circuits. It features V_CEO = −30 V, I_C = −100 mA, h_FE = 200–450 (Class B), V_CE(sat) ≤ −300 mV at I_C = −10 mA/I_B = −0.5 mA, and f_T = 150 MHz - enabling use in audio preamplifiers, relay drivers, and level-shifting interfaces.

For engineers reviewing the BC558B datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92-3 package compatibility, complementary pairing with BC548B, noise performance (NF = 2–10 dB), and thermal derating profile (4.0 mW/°C above 25°C).

Technical Context

The BC558B operates as a medium-gain, medium-voltage PNP bipolar junction transistor optimized for DC-coupled amplification and saturated switching. Its h_FE classification (B: 200–450) ensures predictable current gain across production lots, while V_CEO = −30 V and V_CBO = −30 V define safe operating limits in negative-rail biasing configurations.

Thermal design is constrained by R_JA = 250 °C/W and PD = 500 mW at 25°C, requiring PCB land pattern compliance per FR-4 76 mm × 114 mm reference layout. Noise figure (2–10 dB at 1 kHz) and Cob = 6 pF support stable operation in low-noise analog stages up to mid-RF frequencies.

Key Specifications

Pinout & Package

BC558B is housed in a TO-92-3 plastic package (Case 135AR), with standardized leadform orientation: lead 1 = Collector, lead 2 = Base, lead 3 = Emitter. The package measures 4.83 mm × 4.76 mm and is RoHS-compliant, Pb-free, and halogen-free.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557B and MMBT558, BC558B offers optimal balance of voltage margin, thermal headroom, and through-hole manufacturability - making it preferred for prototyping, education, and legacy board repairs where TO-92 is specified.

Availability

BC558B is available at Aetrix Electronics and suitable for audio preamplifiers, relay drivers, and level-shifting interfaces requiring stable component supply, long-term obsolescence management, and consistent parametric performance across production batches.

Supply support for BC558B 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC558B belongs to onsemi's legacy general-purpose bipolar transistor family, engineered for reliability, consistency, and ease of integration in cost-sensitive analog and mixed-signal designs across decades of industrial deployment.

FAQ

What is the maximum collector-emitter voltage rating for BC558B?

The BC558B has a maximum collector-emitter voltage (V_CEO) rating of −30 V at T_A = 25°C. This value defines the highest reverse-biased voltage the transistor can withstand between collector and emitter while remaining in active or saturated operation. Exceeding this rating risks avalanche breakdown and permanent device damage. Derating applies above 25°C per the thermal characteristics table in the official BC558B datasheet.

Is BC558B pin-compatible with BC548B?

Yes, BC558B is a complementary PNP counterpart to the NPN BC548B, sharing identical TO-92-3 (Case 135AR) package dimensions and pinout: Collector–Base–Emitter (left-to-right, flat side facing viewer). This enables direct substitution in push-pull, differential, and mirror circuits without PCB modification - provided voltage polarity and biasing are adjusted accordingly.

What is the h_FE range for BC558B, and how is it binned?

The BC558B is binned to h_FE Class B, guaranteeing a DC current gain range of 200 to 450 when measured at V_CE = −5 V and I_C = −2 mA. This binning ensures consistent bias point behavior across production units, reducing calibration effort in volume manufacturing. The h_FE value is marked as "B" on the device body and confirmed in the ordering information table of the BC558B datasheet.

Can BC558B be used in audio amplifier stages?

Yes, BC558B is suitable for low-noise audio preamplifier stages due to its specified noise figure of 2–10 dB at 1 kHz (with V_CE = −5 V, I_C = −200 µA, R_G = 2 kΩ). Its h_FE stability, low V_CE(sat), and f_T = 150 MHz support clean gain up to mid-audio frequencies. For best results, operate within its linear region using emitter degeneration and proper decoupling, as validated in BC558B typical performance curves.

What is the thermal resistance and power dissipation limit of BC558B?

The BC558B has a junction-to-ambient thermal resistance (R_JA) of 250 °C/W and a maximum total device dissipation (P_D) of 500 mW at T_A = 25°C. Power dissipation must be derated by 4.0 mW/°C above 25°C. These values assume the recommended FR-4 PCB layout (76 mm × 114 mm, minimum land pattern), as defined in the BC558B thermal characteristics note. Real-world thermal performance depends on copper area and airflow.