onsemi BC557C

Overview

BC557C from onsemi is a PNP silicon small-signal transistor in TO-92 package, rated for −45 V V_CEO, −50 V V_CBO, and −5.0 V V_EBO, with DC current gain (h_FE) of 180–420 at I_C = −10 mA, V_CE = −5.0 V, used in general-purpose amplification and switching circuits including discrete logic inverters and low-power load control.

For engineers reviewing the BC557C datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, TO-92 mechanical compatibility, guaranteed h_FE range, V_CEO rating, and thermal resistance (R_JA = 200°C/W) for ambient-limited designs.

Technical Context

The BC557C operates as a discrete bipolar junction transistor with fixed PNP topology, requiring external base current control to regulate collector-emitter conduction. Its electrical behavior is defined by DC current gain (h_FE), saturation voltages (V_CE(sat) ≤ −0.25 V at I_C = −10 mA, I_B = −0.5 mA), and breakdown limits across all three junctions.

It exhibits f_T = 320 MHz at I_C = −10 mA, V_CE = −5.0 V, supporting audio-frequency amplification and moderate-speed switching. Noise figure is 2.0 dB at I_C = −0.2 mA, V_CE = −5.0 V, R_S = 2.0 kΩ, f = 1 kHz - confirming suitability for low-noise preamplifier stages.

Key Specifications

Pinout & Package

BC557C is housed in TO-92 (Case 29, Style 17) plastic package with 3 leads, standardized for through-hole mounting and manual prototyping. Lead spacing and body dimensions comply with JEDEC TO-92 mechanical specifications (A = 4.45–5.20 mm, B = 4.32–5.33 mm, C = 3.18–4.19 mm).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557B and BC857C, the BC557C offers the highest guaranteed h_FE floor (180) in through-hole format, balancing ease of prototyping, thermal robustness (R_JA = 200°C/W), and gain consistency - making it optimal for production-grade discrete analog and power-control circuits where reliability and testability matter.

Availability

BC557C is available at Aetrix Electronics and suitable for discrete amplifier stages, PNP switching loads, logic level translation, and temperature-stable bias networks requiring stable component supply across industrial, automotive, and consumer electronics programs.

Supply support for BC557C 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, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BC557C belongs to onsemi's legacy BC5xx PNP/NPN transistor family, designed for general-purpose linear amplification and switching in cost-sensitive, high-reliability applications where proven performance and long-term manufacturability are critical.

FAQ

What is the maximum collector-emitter voltage rating for BC557C?

The BC557C has a guaranteed V_CEO rating of −45 V, meaning it can safely block up to 45 V in reverse polarity across collector and emitter terminals before breakdown. This rating applies at I_C = −2.0 mA with base open, and must not be exceeded in circuit design - especially in inductive load switching where flyback spikes could exceed this limit. Always include appropriate clamping if transient risks exist.

Does BC557C have Pb-free packaging?

Yes, the BC557CZL1G variant (and other "G" suffix versions) is explicitly specified as Pb-free in the official onsemi datasheet and complies with RoHS Directive 2011/65/EU. The TO-92 package uses lead-free molding compound and termination plating, qualified for standard lead-free reflow profiles per J-STD-020. Standard BC557C (non-G) is legacy leaded; confirm suffix when ordering.

What is the typical DC current gain (h_FE) of BC557C at 10 mA collector current?

The BC557C is binned to guarantee h_FE between 180 and 420 when tested at I_C = −10 mA and V_CE = −5.0 V. Typical value is 270, but design must accommodate the full min–max range. This wide spread means base resistors should be sized for worst-case h_FE = 180 to ensure saturation in switching applications, while linear amplifiers benefit from the high-end consistency.

Can BC557C be used in audio amplifier circuits?

Yes, BC557C is suitable for low-noise audio preamplifier stages due to its 2.0 dB noise figure at 1 kHz, f_T = 320 MHz, and stable h_fe characteristics. It performs well in common-emitter configurations with emitter degeneration, delivering flat frequency response up to ~100 kHz. Avoid use in high-power output stages - its 625 mW P_D rating limits it to line-level or microphone-level signal conditioning.

What is the thermal resistance (R_JA) of BC557C in free-air conditions?

The BC557C has a specified R_JA of 200°C/W under natural convection (free-air) conditions, meaning junction temperature rises 200°C for every watt dissipated without heatsinking. At its rated 625 mW maximum power, this yields a theoretical ΔT of 125°C above ambient - so operation at full power requires ambient ≤ 25°C to stay within the −55°C to +150°C T_J limit. Derate linearly above 25°C per 5.0 mW/°C.