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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi BC557BU

Name: BC557BU
Brand: onsemi
SKU: BC557BU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC557BU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 (TO-226AA)

Datasheet:: BC557BU.pdf

Description:: TRANS PNP 45V 0.1A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:2,780

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Product details

Overview

BC557BU from onsemi is a PNP epitaxial silicon transistor designed for general-purpose switching and linear amplification in low-power analog and digital circuits. It features V_CEO = −45 V, I_C = −100 mA, h_FE = 110–800 (Class A/B/C), V_CE(sat) = −90 to −650 mV, and f_T = 150 MHz - enabling use in audio preamplifiers, level shifters, and discrete logic interfaces.

For engineers reviewing the BC557BU datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92-3 (case 135AR) package, complementary pairing with BC547/BC548 NPN devices, low-noise capability (NF = 2–10 dB at 1 kHz), and RoHS-compliant Pb-free construction.

Technical Context

The BC557BU operates as a medium-voltage, medium-current PNP bipolar junction transistor with DC current gain spanning three h_FE classifications (A: 110–220, B: 200–450, C: 420–800). Its V_CEO = −45 V and V_CBO = −50 V support operation in negative-rail biasing schemes up to −45 V collector-emitter differential.

Thermal performance is defined by R_JA = 250 °C/W (FR-4 PCB, 76 mm × 114 mm), PD = 500 mW at 25°C with 4.0 mW/°C derating. Electrical behavior includes low V_BE(on) (−600 to −750 mV at I_C = −2 mA) and Cob = 6 pF at V_CB = −10 V, supporting stable high-frequency small-signal amplification.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−45 V: Maximum safe collector-emitter reverse voltage before breakdown in common-emitter configuration.
I_C (DC)	−100 mA: Continuous collector current rating defining linear and switching load capacity.
h_FE	110–800: DC current gain range across Class A/B/C variants, directly affecting base drive requirements.
f_T	150 MHz: Unity-gain bandwidth at V_CE = −5 V, I_C = −10 mA - sets upper limit for small-signal amplification.
V_CE(sat)	−90 to −650 mV: Saturation voltage at I_C = −10 mA / −100 mA - determines power loss and logic-level compatibility in switch mode.
C_ob	6 pF: Output capacitance at V_CB = −10 V - impacts high-frequency response and stability in amplifier stages.

Pinout & Package

BC557BU is housed in a TO-92-3 plastic package (case 135AR), with leads formed for through-hole mounting. Pin identification follows standard orientation: flat side facing viewer, leads down, left-to-right = Collector (1), Base (2), Emitter (3).

Pin/Terminal	Circuit Role	Design Meaning
1 (Left)	Collector	Main current sink terminal; connects to negative supply rail or load return path in PNP configurations.
2 (Center)	Base	Control input; requires current-limited negative bias to turn on conduction between collector and emitter.
3 (Right)	Emitter	Current source terminal; typically tied to ground or positive rail depending on circuit topology.

Key Features

Feature	Design Value
Complementary Pairing	Designed as direct PNP counterpart to BC546–BC550 NPN series - enables matched push-pull and differential pair designs.
Low-Noise Operation	NF = 2–10 dB at 1 kHz (I_C = −200 µA), making it suitable for microphone preamps and sensor signal conditioning where SNR matters.
Pb-Free & RoHS Compliance	Meets EU RoHS Directive 2011/65/EU and halogen-free/BFR-free requirements - supports environmentally compliant manufacturing.
High-Voltage Capability	V_CBO = −50 V and V_CEO = −45 V allow reliable operation in −45 V rail systems without derating or external protection.

Applications

Audio Preamp Stage	Discrete Logic Level Shifter
Use Scenario: Amplifying weak signals from electret microphones or piezoelectric sensors in battery-powered voice recorders. IC Role / Device Role / Timing Role: Small-signal PNP amplifier operating in common-emitter configuration with emitter degeneration. Use Value: Low noise (2–10 dB NF) and stable h_FE ensure high-fidelity gain without introducing audible hiss or distortion.	Use Scenario: Translating TTL/CMOS logic levels between +3.3 V and −5 V domains in legacy industrial controllers. IC Role / Device Role / Timing Role: Active pull-up switch with base driven by positive logic, emitter referenced to −5 V rail. Use Value: V_CEO = −45 V safely accommodates −5 V rail while maintaining fast edge response (f_T = 150 MHz).
LED Driver Switch	Current Mirror Reference
Use Scenario: Driving indicator LEDs from microcontroller GPIO pins in automotive body control modules. IC Role / Device Role / Timing Role: Saturated PNP switch controlling LED anode connection to positive supply. Use Value: V_CE(sat) ≤ −300 mV at I_C = −10 mA minimizes power dissipation and ensures full LED brightness.	Use Scenario: Building precision current mirrors in analog front-ends for sensor signal scaling and offset correction. IC Role / Device Role / Timing Role: Matched PNP transistor in emitter-coupled configuration with BC557B or BC557C variants. Use Value: Tight h_FE classification (B: 200–450 or C: 420–800) enables <1% mirror ratio error over temperature.

Audio Preamp Stage

Discrete Logic Level Shifter

Use Scenario: Amplifying weak signals from electret microphones or piezoelectric sensors in battery-powered voice recorders.

IC Role / Device Role / Timing Role: Small-signal PNP amplifier operating in common-emitter configuration with emitter degeneration.

Use Value: Low noise (2–10 dB NF) and stable h_FE ensure high-fidelity gain without introducing audible hiss or distortion.

Use Scenario: Translating TTL/CMOS logic levels between +3.3 V and −5 V domains in legacy industrial controllers.

IC Role / Device Role / Timing Role: Active pull-up switch with base driven by positive logic, emitter referenced to −5 V rail.

Use Value: V_CEO = −45 V safely accommodates −5 V rail while maintaining fast edge response (f_T = 150 MHz).

LED Driver Switch

Current Mirror Reference

Use Scenario: Driving indicator LEDs from microcontroller GPIO pins in automotive body control modules.

IC Role / Device Role / Timing Role: Saturated PNP switch controlling LED anode connection to positive supply.

Use Value: V_CE(sat) ≤ −300 mV at I_C = −10 mA minimizes power dissipation and ensures full LED brightness.

Use Scenario: Building precision current mirrors in analog front-ends for sensor signal scaling and offset correction.

IC Role / Device Role / Timing Role: Matched PNP transistor in emitter-coupled configuration with BC557B or BC557C variants.

Use Value: Tight h_FE classification (B: 200–450 or C: 420–800) enables <1% mirror ratio error over temperature.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC557BTA	Same die, identical electrical specs; differs only in packaging - fan-fold tape instead of bulk.	No functional difference; used interchangeably where tape-and-reel automation is required.	Select BC557BTA for automated SMT-compatible assembly; BC557BU is optimized for manual or selective soldering workflows.
BC558BTA	V_CEO = −30 V (vs. −45 V), V_CBO = −30 V - lower voltage rating; otherwise identical h_FE, f_T, and noise performance.	Suitable only in ≤−30 V systems; not recommended for −45 V rail applications without redesign.	Choose BC558BTA only when system voltage is capped at −30 V and cost sensitivity outweighs margin requirements.

Compared with BC557BTA and BC558BTA, the BC557BU offers identical core transistor performance but with bulk packaging for prototyping and low-volume production, while providing higher voltage headroom than BC558BTA - critical for robustness in −45 V industrial signal chains.

Availability

BC557BU is available at Aetrix Electronics and suitable for audio preamplifiers, discrete logic level shifters, and LED driver switches requiring stable component supply, long-term obsolescence management, and RoHS-compliant sourcing.

Supply support for BC557BU 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 BC557BU belongs to onsemi's legacy general-purpose bipolar transistor family, engineered for reliability, consistency, and broad compatibility in discrete analog and mixed-signal designs across decades of industrial deployment.

FAQ

What is the maximum collector-emitter voltage rating for BC557BU?

The BC557BU has a maximum collector-emitter voltage (V_CEO) rating of −45 V at T_A = 25°C. This rating applies under standard test conditions and must be derated at elevated ambient temperatures per the thermal characteristics table. Exceeding −45 V risks irreversible breakdown. The BC557BU datasheet confirms this value in the Absolute Maximum Ratings section, and it is consistent across all BC557 variants regardless of h_FE class.

Is BC557BU pin-compatible with BC547 or other complementary transistors?

Yes - the BC557BU shares identical TO-92-3 (case 135AR) pinout (C-B-E) with BC547, BC548, and other members of the BC5xx complementary family. However, polarity differs: BC557BU is PNP while BC547 is NPN. Direct replacement requires circuit topology adjustment (e.g., swapping supply rails and signal polarity), but mechanical layout and footprint remain unchanged.

Does BC557BU support low-noise audio applications?

Yes - the BC557BU exhibits a noise figure (NF) of 2–10 dB at 1 kHz with I_C = −200 µA and R_G = 2 kΩ, as specified in the Electrical Characteristics table. This performance is confirmed for BC556/BC557/BC558 variants and makes the BC557BU suitable for microphone preamplifiers, sensor amplifiers, and other low-level analog signal paths where signal integrity is critical.

What h_FE classification does BC557BU belong to?

The BC557BU is available in multiple h_FE classifications - A (110–220), B (200–450), and C (420–800) - indicated by the final letter in the full part number (e.g., BC557BU may be marked BC557A, BC557B, or BC557C). The "BU" suffix denotes bulk packaging but does not specify gain class; users must verify marking or ordering code to confirm h_FE bin.

Can BC557BU be used in surface-mount designs?

No - the BC557BU is supplied in a through-hole TO-92-3 package (case 135AR) and is not designed for surface-mount assembly. While some customers adapt TO-92 devices to SMT footprints using adapters or reflow-compatible epoxy, the BC557BU itself lacks SMT-compatible terminations or thermal profiles. For SMT alternatives, consider onsemi's MMBT557 or similar SOT-23 PNP transistors.

BC557BU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA)

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 100 mA

Voltage - Collector Emitter Breakdown (Max):: 45 V

Vce Saturation (Max) @ Ib, Ic:: 650mV @ 5mA, 100mA

Current - Collector Cutoff (Max):: 15nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 110 @ 2mA, 5V

Power - Max:: 500 mW

Frequency - Transition:: 150MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

BC557BU FAQ

1.How can I place an order for BC557BU through Aetrix?

Please submit a Request for Quotation (RFQ) for BC557BU on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for BC557BU reliable?

The price and inventory of BC557BU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC557BU is usually 5 days.

3.What payment methods are accepted for BC557BU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC557BU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC557BU?

BC557BU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC557BU order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for BC557BU?

For technical support, including BC557BU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC557BU requirements.

6.How does Aetrix verify that BC557BU is sourced from the original manufacturer or authorized distributors?

All BC557BU products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that BC557BU meets industry standards.

7.What is the process for return or replacement of BC557BU?

All BC557BU units undergo pre-shipment inspection (PSI). If there is an issue with BC557BU, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The BC557BU part is unused and in its original packaging.

Return procedure for BC557BU:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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