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

onsemi BC557

Name: BC557
Brand: onsemi
SKU: BC557
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC557

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BC557.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:5,444

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Product details

Overview

BC557 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 = −45 V, I_C = −100 mA, h_FE range of 110–800 (depending on grade), V_CE(sat) ≤ −300 mV at I_C = −10 mA / I_B = −0.5 mA, and f_T = 150 MHz - enabling use in audio preamps, relay drivers, and level-shifting interfaces.

For engineers reviewing the BC557 datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92-3 package compatibility, complementary pairing with BC547/BC548 NPN devices, low-noise performance (NF = 2–10 dB at 1 kHz), and RoHS-compliant Pb-free construction suitable for industrial and consumer-grade designs.

Technical Context

The BC557 operates as a medium-gain, medium-voltage PNP bipolar junction transistor optimized for DC-coupled amplification and saturated switching. Its h_FE classification (A/B/C) defines gain spread, while V_CEO = −45 V and V_CBO = −50 V establish safe operating limits for negative-rail biasing in dual-supply or single-supply inverted configurations.

Thermal design is constrained by R_JA = 250 °C/W and P_D = 500 mW at T_A = 25 °C, with linear derating of 4.0 mW/°C above ambient. The device exhibits Cob = 6 pF at V_CB = −10 V, supporting stable operation up to mid-VHF frequencies when used in tuned amplifier stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−45 V: Maximum collector-emitter voltage before breakdown in common-emitter configuration; supports rail-to-rail signal swing in −40 V systems.
I_C (DC)	−100 mA: Continuous collector current rating; sufficient for driving LEDs, small relays, or logic-level translators without heatsinking.
h_FE	110–800: DC current gain range across A/B/C grades; enables predictable biasing in Class-A amplifiers or robust saturation in switch mode.
V_CE(sat)	−300 mV max at I_C = −10 mA / I_B = −0.5 mA: Low saturation voltage ensures minimal power loss and high efficiency in switching applications.
f_T	150 MHz: Current gain bandwidth product; permits stable small-signal amplification up to ~10–20 MHz with proper compensation.
C_ob	6 pF at V_CB = −10 V: Output capacitance affects high-frequency roll-off and stability in RF-coupled stages or oscillator feedback paths.
NF	2–10 dB at 1 kHz: Noise figure specifies low-noise capability for audio preamplifier front-ends where signal integrity is critical.

Pinout & Package

BC557 is housed in a TO-92-3 plastic package (case 135AR), with standardized leadform: flat side facing viewer, leads downward, left-to-right pin order: Collector (1), Base (2), Emitter (3).

Pin/Terminal	Circuit Role	Design Meaning
1 - Collector	Current sink terminal	Connected to most negative potential in circuit; handles full load current and must be routed with adequate copper area for thermal dissipation.
2 - Base	Control input	Receives forward-biased current to turn on transistor; requires series resistor to limit I_B and prevent damage during saturation.
3 - Emitter	Current source terminal	Typically tied to ground or positive rail in PNP configurations; provides reference point for bias network and emitter degeneration.

Key Features

Feature	Design Value
Complementary pairing	Matched as PNP counterpart to BC547/BC548 NPN transistors, enabling balanced push-pull output stages and differential amplifiers.
Low-noise operation	NF = 2–10 dB at 1 kHz allows use in microphone preamps and sensor signal conditioning without added noise degradation.
Pb-free & RoHS compliant	Fully compliant with EU RoHS Directive 2011/65/EU and halogen-free/BFR-free requirements for environmentally regulated production.
High-voltage tolerance	V_CBO = −50 V and V_CEO = −45 V support reliable operation in −36 V industrial control rails and legacy telecom supplies.
TO-92 mechanical standardization	Case 135AR footprint ensures drop-in replacement across BC556–BC560 family and compatibility with automated assembly equipment.

Applications

Audio Signal Amplification	Relay & Solenoid Driving
Use Scenario: Low-noise preamplification of electret microphone outputs in portable voice recorders and intercom systems. IC Role / Device Role / Timing Role: PNP common-emitter amplifier providing 20–40 dB voltage gain with minimal added noise. Use Value: NF = 2–10 dB at 1 kHz preserves signal fidelity; h_FE ≥ 110 ensures stable bias under battery-voltage drift.	Use Scenario: Saturated switching of 12 V/50 mA electromagnetic relays in PLC I/O modules and HVAC controllers. IC Role / Device Role / Timing Role: PNP switch controlling relay coil current with base-driven saturation. Use Value: V_CE(sat) ≤ −300 mV minimizes coil power loss; I_C = −100 mA exceeds typical relay hold current.
Level Shifting Interface	Discrete Logic Inversion
Use Scenario: Translating 3.3 V CMOS logic signals to −5 V TTL-compatible levels in mixed-voltage test equipment. IC Role / Device Role / Timing Role: Emitter-follower or common-base level translator handling bidirectional voltage inversion. Use Value: V_CEO = −45 V accommodates wide negative rail margins; f_T = 150 MHz supports >1 MHz digital edge rates.	Use Scenario: Implementing NOT gates and simple combinational logic in repairable analog-digital hybrid boards. IC Role / Device Role / Timing Role: Discrete inverter stage using fixed-base bias and emitter resistor pull-up. Use Value: h_FE ≥ 110 ensures clean logic transitions; TO-92 package allows manual replacement without PCB redesign.

Audio Signal Amplification

Relay & Solenoid Driving

Use Scenario: Low-noise preamplification of electret microphone outputs in portable voice recorders and intercom systems.

IC Role / Device Role / Timing Role: PNP common-emitter amplifier providing 20–40 dB voltage gain with minimal added noise.

Use Value: NF = 2–10 dB at 1 kHz preserves signal fidelity; h_FE ≥ 110 ensures stable bias under battery-voltage drift.

Use Scenario: Saturated switching of 12 V/50 mA electromagnetic relays in PLC I/O modules and HVAC controllers.

IC Role / Device Role / Timing Role: PNP switch controlling relay coil current with base-driven saturation.

Use Value: V_CE(sat) ≤ −300 mV minimizes coil power loss; I_C = −100 mA exceeds typical relay hold current.

Level Shifting Interface

Discrete Logic Inversion

Use Scenario: Translating 3.3 V CMOS logic signals to −5 V TTL-compatible levels in mixed-voltage test equipment.

IC Role / Device Role / Timing Role: Emitter-follower or common-base level translator handling bidirectional voltage inversion.

Use Value: V_CEO = −45 V accommodates wide negative rail margins; f_T = 150 MHz supports >1 MHz digital edge rates.

Use Scenario: Implementing NOT gates and simple combinational logic in repairable analog-digital hybrid boards.

IC Role / Device Role / Timing Role: Discrete inverter stage using fixed-base bias and emitter resistor pull-up.

Use Value: h_FE ≥ 110 ensures clean logic transitions; TO-92 package allows manual replacement without PCB redesign.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC557BTA	Same die, identical electrical specs, TO-92-3 case 135AR, fan-fold packaging instead of tape & reel.	No functional difference; differs only in shipping format and reel orientation.	Select BC557BTA for manual prototyping or low-volume hand assembly where tape-and-reel feed is unnecessary.
BC558BTF	V_CEO = −30 V (vs. −45 V), V_CBO = −30 V (vs. −50 V); otherwise matched h_FE, f_T, and package.	Not suitable for −40 V rail applications; limited to ≤ −24 V systems due to lower breakdown ratings.	Choose BC558BTF only when supply voltage is capped at −24 V and cost sensitivity outweighs voltage headroom needs.

Compared with BC557BTF, BC557BTA offers identical performance with alternate packaging for flexibility in assembly methods, while BC558BTF trades 15 V of collector-emitter voltage margin for marginal cost reduction - making BC557BTF the optimal choice for designs requiring robust −45 V operation.

Availability

BC557 is available at Aetrix Electronics and suitable for audio preamplification, relay driving, and level-shifting interfaces requiring stable component supply, long-term obsolescence resilience, and RoHS-compliant manufacturing.

Supply support for BC557 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 manufacturer specializing in energy-efficient power management, analog, and discrete components for automotive, industrial, and consumer markets.

The BC557 belongs to onsemi's legacy general-purpose bipolar transistor family, engineered for reliability, manufacturability, and broad compatibility in cost-sensitive analog and mixed-signal designs.

FAQ

What is the maximum collector-emitter voltage rating for BC557?

The BC557 has a guaranteed V_CEO rating of −45 V at T_A = 25 °C. This value is specified in the Absolute Maximum Ratings table of the official onsemi datasheet (Rev. 3, June 2024) and defines the upper limit for safe DC operation in common-emitter configuration. Exceeding this voltage risks avalanche breakdown and permanent device failure.

Is BC557 compatible with BC547 in complementary amplifier designs?

Yes, BC557 is explicitly designed as the PNP complement to the NPN BC547, sharing matching h_FE ranges, thermal characteristics, and TO-92 packaging. The onsemi datasheet confirms this complementary pairing for push-pull output stages and differential amplifiers, ensuring symmetrical gain and offset behavior when both devices are used together in the same circuit.

What does the "B" suffix in BC557BTF indicate?

The "B" in BC557BTF denotes the h_FE gain classification - specifically, a DC current gain range of 200–450 at I_C = −2 mA and V_CE = −5 V. The "TF" suffix indicates tape-and-reel packaging in TO-92-3 case 135AR, per onsemi's ordering nomenclature defined on page 2 of the BC556–BC560 datasheet.

Can BC557 be used in low-noise audio applications?

Yes, BC557 is rated for noise figure (NF) of 2–10 dB at 1 kHz with V_CE = −5 V and I_C = −200 µA, making it suitable for low-noise preamplifier stages. Its low-noise performance is confirmed in the Electrical Characteristics table and is shared with BC556 and BC558 - distinguishing it from higher-noise variants like BC559/BC560.

What is the thermal resistance junction-to-ambient for BC557 in TO-92 package?

The BC557 in TO-92-3 (case 135AR) has a specified thermal resistance R_JA of 250 °C/W under standard PCB conditions (FR-4, 76 mm × 114 mm, minimum land pattern). This value is listed in the Thermal Characteristics section and governs allowable power dissipation: P_D derates linearly at 4.0 mW/°C above 25 °C ambient.

BC557 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

BC557 FAQ

1.How can I place an order for BC557 through Aetrix?

Please submit a Request for Quotation (RFQ) for BC557 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 BC557 reliable?

The price and inventory of BC557 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC557 is usually 5 days.

3.What payment methods are accepted for BC557?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC557 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC557?

BC557 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC557 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 BC557?

For technical support, including BC557 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC557 requirements.

6.How does Aetrix verify that BC557 is sourced from the original manufacturer or authorized distributors?

All BC557 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 BC557 meets industry standards.

7.What is the process for return or replacement of BC557?

All BC557 units undergo pre-shipment inspection (PSI). If there is an issue with BC557, 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 BC557 part is unused and in its original packaging.

Return procedure for BC557:

1.Submit a request within 90 days.

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

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