onsemi BC557BG

Overview

BC557BG from onsemi is a PNP silicon general-purpose amplifier transistor in TO-92 package, rated for −45 V V_CEO, −50 V V_CBO, −5.0 V V_EBO, −100 mA I_C, and 625 mW P_D at T_A = 25°C. It delivers h_FE = 120–800 (at I_C = −10 mA, V_CE = −5 V), f_T = 320 MHz, and V_CE(sat) ≤ −0.3 V (I_C = −10 mA, I_B = −0.5 mA), widely used in low-voltage signal amplification and switching circuits.

For engineers reviewing the BC557BG datasheet, pinout, applications, or equivalent options, this page provides verified electrical parameters, TO-92 terminal mapping, real-world use cases in discrete gain stages and level-shifting interfaces, and two validated alternative PNP transistors with documented parameter differences.

Technical Context

The BC557BG operates as a medium-speed, medium-current PNP bipolar junction transistor optimized for linear amplification and saturated switching. Its DC current gain spans three variants (A/B/C), with B-series offering h_FE = 120–270 at I_C = −2 mA and 170–500 at I_C = −100 mA, enabling stable biasing across load conditions.

Small-signal performance includes f_T = 320 MHz (I_C = −10 mA, V_CE = −5 V), C_ob = 3.0–6.0 pF (V_CB = −10 V), and NF = 2.0 dB (I_C = −0.2 mA, R_S = 2 kΩ, f = 1 kHz), supporting audio-frequency and low-MHz analog signal paths with low noise and predictable bandwidth.

Key Specifications

Pinout & Package

BC557BG uses the TO-92 (Case 29, Style 17) plastic package with bent leads, Pb-free finish, and standard 3-pin through-hole configuration. Dimensions: 4.45–5.20 mm (L) × 4.32–5.33 mm (W) × 3.18–4.19 mm (H).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557BRL1G, BC557BG offers identical performance in bulk-packaged form ideal for lab evaluation and low-volume builds; versus MMBT557LT1G, BC557BG delivers 2× higher power dissipation and simpler thermal design in TO-92, making it more suitable for production-grade discrete amplifiers and switches.

Availability

BC557BG is available at Aetrix Electronics and suitable for audio signal conditioning, industrial level-shifting interfaces, and LED driver circuits requiring stable component supply, long-term obsolescence management, and RoHS-compliant sourcing.

Supply support for BC557BG 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 BC557BG belongs to the BC556/557/558 family of general-purpose PNP transistors designed for cost-sensitive, high-reliability linear and switching applications in consumer electronics, instrumentation, and power management subsystems.

FAQ

What is the maximum collector-emitter voltage rating for BC557BG?

The BC557BG has a maximum collector-emitter voltage (V_CEO) rating of −45 Vdc. This value is confirmed in the "Maximum Ratings" table of the official onsemi datasheet (Rev. 3, March 2007) and defines the absolute upper limit for reverse-biased collector-to-emitter voltage before breakdown occurs. Exceeding −45 V risks permanent device damage, and design margins should maintain operation below −40 V in production circuits.

Does BC557BG have a guaranteed minimum h_FE at I_C = −100 mA?

Yes, BC557BG (B-series) guarantees h_FE ≥ 170 at I_C = −100 mA, V_CE = −5.0 V, and T_A = 25°C, per the "ELECTRICAL CHARACTERISTICS" table. This minimum ensures predictable base drive requirements in high-current switching applications, such as driving relays or power LEDs, without risk of incomplete saturation.

What is the thermal resistance from junction to ambient (R_JA) for BC557BG?

The BC557BG has a thermal resistance R_JA of 200 °C/W when mounted on a standard FR-4 PCB with no heatsink, as specified in the "THERMAL CHARACTERISTICS" section. This value assumes natural convection cooling and must be derated by 5.0 mW/°C above 25°C ambient to maintain safe junction temperature within the −55°C to +150°C operating range.

Is BC557BG compatible with lead-free soldering processes?

Yes, BC557BG is explicitly marked as Pb-free in the ordering information and features a Pb-free finish compliant with JEDEC J-STD-020 moisture sensitivity level (MSL) 1. It supports standard lead-free reflow profiles up to 260°C peak temperature, with no special pre-bake required, as confirmed in the "ORDERING INFORMATION" and "Pb−Free Packages" notes of the onsemi datasheet.

How does BC557BG differ from BC557C in terms of DC current gain?

BC557BG (B-series) specifies h_FE = 170–500 at I_C = −100 mA, while BC557CG (C-series) guarantees h_FE = 290–800 under identical conditions. The C-series offers higher minimum gain for ultra-low-base-drive applications, whereas the B-series provides tighter mid-range gain consistency-both share identical voltage, current, power, and frequency ratings.