onsemi BC557CG

Overview

BC557CG from onsemi is a PNP silicon general-purpose amplifier transistor in TO-92 package, rated for −45 V collector-emitter voltage, −50 V collector-base voltage, and −5.0 V emitter-base voltage, with DC current gain (h_FE) of 180–420 at −10 mA/−5 V, 320 MHz transition frequency, and 625 mW power dissipation at 25°C ambient - used in low-voltage analog amplification and switching circuits in consumer and industrial electronics.

For engineers reviewing the BC557CG datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, TO-92 terminal mapping, real-world use cases in signal conditioning and level shifting, and two validated alternative parts with documented functional and parametric differences.

Technical Context

The BC557CG operates as a medium-gain, medium-speed PNP bipolar junction transistor optimized for linear amplification and saturated switching. Its h_FE range (180–420) supports stable biasing across production lots, while f_T = 320 MHz enables audio-frequency and low-MHz signal handling. The device features low V_CE(sat) (−0.25 V max at −10 mA/−0.5 mA) and V_BE(sat) (−0.7 V max), ensuring efficient operation in low-power active circuits.

Thermal design is constrained by R_JA = 200°C/W and R_JC = 83.3°C/W, requiring heatsinking only above ~300 mW continuous dissipation. Junction temperature range (−55°C to +150°C) and robust breakdown ratings (V_(BR)CEO = −45 V, V_(BR)CBO = −50 V) support reliable operation in non-automotive industrial environments.

Key Specifications

Pinout & Package

BC557CG uses the TO-92 (Case 29, Style 17) plastic package with bent leads, Pb-free finish, and standard 0.1" lead pitch. Dimensions: 4.45–5.20 mm length × 4.32–5.33 mm width × 3.18–4.19 mm height.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557CG, BC557B offers lower gain consistency but identical reliability and thermal behavior, while MMBT557 trades TO-92 mechanical robustness and power handling for SMT compatibility - making BC557CG optimal for through-hole prototyping and thermally demanding analog stages.

Availability

BC557CG is available at Aetrix Electronics and suitable for audio pre-amplification, level-shifting interfaces, current mirror references, and discrete op-amp input stages requiring stable component supply, long-term obsolescence management, and RoHS-compliant sourcing.

Supply support for BC557CG 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 management, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC557CG belongs to onsemi's legacy BC5xx family of general-purpose bipolar transistors, designed for broad adoption in discrete analog signal conditioning, switching, and biasing circuits where reliability, gain consistency, and thermal resilience are critical.

FAQ

What is the maximum collector-emitter voltage rating for BC557CG?

The BC557CG has a maximum collector-emitter voltage (V_CEO) rating of −45 V DC. This value is confirmed in the "Maximum Ratings" table of the official onsemi datasheet (Rev. 3, March 2007). Exceeding this voltage risks irreversible avalanche breakdown. Designers must ensure that the BC557CG's V_CE never exceeds −45 V under any operating condition, including transient spikes.

Does BC557CG support lead-free soldering processes?

Yes, BC557CG is explicitly marked as Pb-free in the ordering information section and complies with RoHS Directive 2011/65/EU. Its TO-92 package is qualified for lead-free reflow soldering with peak temperatures up to 260°C, as stated in onsemi's Soldering and Mounting Techniques Reference Manual. No special pre-treatment or flux is required beyond standard Pb-free process guidelines.

What is the typical transition frequency (f_T) of BC557CG and how is it measured?

The BC557CG has a typical transition frequency (f_T) of 320 MHz, measured at I_C = −10 mA, V_CE = −5.0 V, and f = 100 MHz, per the "Electrical Characteristics" table. This parameter reflects the frequency at which the small-signal current gain (h_fe) drops to unity, indicating usable bandwidth for amplification. It is not guaranteed minimum/maximum but represents the center of the production distribution.

How does the h_FE range of BC557CG compare to BC557A and BC557B?

The BC557CG has an h_FE range of 180–420 at −10 mA/−5 V, which sits between BC557A (120–270) and BC557B (150–290) in the same family. This higher gain band makes BC557CG preferable for applications requiring tighter bias point control or higher open-loop gain without feedback adjustment. All three share identical voltage, power, and frequency ratings.

Can BC557CG be used in place of BC557B in existing designs?

Yes, BC557CG is a direct functional upgrade to BC557B with identical pinout, package, voltage/current ratings, and thermal characteristics - only h_FE is extended (180–420 vs. 150–290). No PCB or schematic changes are needed. However, designers should verify that the higher gain does not cause unintended saturation or instability in feedback loops calibrated for BC557B's lower h_FE median.