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

NXP Semiconductors BC557B,126

Name: BC557B,126
Brand: NXP Semiconductors
SKU: BC557B,126
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC557B,126

Manufacturer:: NXP Semiconductors

Category:: Single Bipolar Transistors

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

Datasheet:: BC557B,126.pdf

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

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Product details

Overview

BC557B,126 from NXP Semiconductors is a PNP general-purpose bipolar junction transistor in TO-92 (SOT54) package, rated for −45 V V_CEO, −100 mA I_C, and 500 mW P_tot, with h_FE range 220–475 at I_C = −2 mA, used in low-voltage switching and small-signal amplification circuits.

For engineers reviewing the BC557B,126 datasheet, BC557B,126 pinout, BC557B,126 application, or BC557B,126 equivalent, key selection criteria include its PNP polarity, TO-92 mechanical compatibility, DC current gain binning (B-grade), saturation voltage performance at −10 mA/−0.5 mA, and thermal resistance of 250 K/W on FR4 PCB.

Technical Context

The BC557B,126 operates as a silicon PNP BJT with fixed emitter-base and collector-base junctions optimized for linear amplification and saturated switching in low-power analog and digital logic interface stages. Its design targets stable h_FE across −2 mA to −100 mA collector currents and predictable V_CEsat below −300 mV under standard drive conditions.

It shares pinout and package dimensions with BC556/BC557 family variants but differs in h_FE binning and absolute maximum ratings-specifically lower V_CEO (−45 V vs −65 V for BC556) and V_CBO (−50 V vs −80 V), reflecting its targeted use in sub-45 V rail applications.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−45 V: Maximum allowable collector-emitter voltage before breakdown in open-base configuration.
I_C (DC)	−100 mA: Continuous collector current limit defining safe linear/saturation operation without thermal runaway.
h_FE	220–475 @ I_C = −2 mA, V_CE = −5 V: Confirmed DC current gain range for B-grade bin, enabling predictable base drive sizing.
V_CEsat	−60 to −300 mV @ I_C = −10 mA, I_B = −0.5 mA: Low saturation voltage ensures minimal power loss in switching mode.
P_tot	500 mW @ T_amb ≤ 25 °C: Total dissipation limit requiring derating above ambient temperature per R_th(j-a) = 250 K/W.
f_T	100 MHz: Transition frequency confirming usable bandwidth up to audio and low-RF signal amplification.

Pinout & Package

BC557B,126 is housed in a plastic single-ended leaded through-hole package (TO-92 / SOT54 / SC-43A), with 3 leads spaced on 2.54 mm pitch, total length 14.5 mm, body width 4.8 mm, and lead diameter 0.48 mm.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Current exit terminal in PNP operation; connected to most positive rail in common-emitter switch configurations.
2	Base	Control terminal; requires negative bias relative to emitter to enable conduction; typical drive current −0.5 mA for 10 mA collector sink.
3	Collector	Current entry terminal; tied to load and supply rail in switching applications; handles full load current path when saturated.

Key Features

Feature	Design Value
PNP polarity	Enables high-side switching and complementary pair use with NPN BC547/BC546 in push-pull stages.
TO-92 mechanical standardization	Ensures drop-in replacement capability across legacy designs using industry-standard through-hole footprint and hand-soldering compatibility.
B-grade h_FE binning	Guarantees minimum h_FE of 220, reducing base drive uncertainty in production-critical amplifier and logic-level translation circuits.
Low V_CEsat	Supports efficient switching in battery-powered systems where <300 mV saturation loss preserves operating voltage headroom.

Applications

Audio Pre-amplifier Stage	Microcontroller GPIO Level Shifter
Use Scenario: Amplifying weak microphone signals (≤10 mV) into line-level outputs for ADC input. IC Role / Device Role / Timing Role: Small-signal PNP amplifier in common-emitter configuration with emitter degeneration resistor. Use Value: h_FE ≥220 ensures stable gain control; f_T = 100 MHz supports full audio band (20 Hz–20 kHz) with margin.	Use Scenario: Converting 3.3 V logic-high from MCU to −5 V active-low output for legacy TTL-compatible peripherals. IC Role / Device Role / Timing Role: Inverting level translator with base driven by MCU pin, collector pulled to −5 V rail. Use Value: V_CEO = −45 V safely exceeds −5 V rail; V_CEsat ≤ −300 mV guarantees clean logic-low assertion.
Relay Driver Circuit	LED Current Sink Switch
Use Scenario: Driving 12 V, 40 mA coil relay from microcontroller output via base resistor network. IC Role / Device Role / Timing Role: Saturated PNP switch with collector connected to relay coil and +12 V, emitter to ground. Use Value: I_C = −100 mA rating accommodates relay surge current; low V_CEsat minimizes coil voltage drop during activation.	Use Scenario: Controlling 20 mA red LED string from 5 V supply in indicator panel with active-low enable. IC Role / Device Role / Timing Role: Constant-current sink switch with emitter grounded, collector feeding LED anode, base driven low to illuminate. Use Value: h_FE bin enables precise base resistor calculation; TO-92 package allows manual assembly in space-constrained panels.

Audio Pre-amplifier Stage

Microcontroller GPIO Level Shifter

Use Scenario: Amplifying weak microphone signals (≤10 mV) into line-level outputs for ADC input.

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

Use Value: h_FE ≥220 ensures stable gain control; f_T = 100 MHz supports full audio band (20 Hz–20 kHz) with margin.

Use Scenario: Converting 3.3 V logic-high from MCU to −5 V active-low output for legacy TTL-compatible peripherals.

IC Role / Device Role / Timing Role: Inverting level translator with base driven by MCU pin, collector pulled to −5 V rail.

Use Value: V_CEO = −45 V safely exceeds −5 V rail; V_CEsat ≤ −300 mV guarantees clean logic-low assertion.

Relay Driver Circuit

LED Current Sink Switch

Use Scenario: Driving 12 V, 40 mA coil relay from microcontroller output via base resistor network.

IC Role / Device Role / Timing Role: Saturated PNP switch with collector connected to relay coil and +12 V, emitter to ground.

Use Value: I_C = −100 mA rating accommodates relay surge current; low V_CEsat minimizes coil voltage drop during activation.

Use Scenario: Controlling 20 mA red LED string from 5 V supply in indicator panel with active-low enable.

IC Role / Device Role / Timing Role: Constant-current sink switch with emitter grounded, collector feeding LED anode, base driven low to illuminate.

Use Value: h_FE bin enables precise base resistor calculation; TO-92 package allows manual assembly in space-constrained panels.

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
BC557C,126	Higher h_FE range (420–800) and same package; identical V_CEO/I_C ratings.	Preferred where higher gain reduces base drive burden, e.g., high-impedance sensor interfaces.	Select BC557C,126 only if circuit requires >420 h_FE; BC557B,126 offers tighter gain consistency at lower cost.
MMBT557LT1G	SOT-23 surface-mount package; same h_FE bin (220–475); V_CEO = −45 V, I_C = −100 mA.	Used in space-constrained PCBs where through-hole TO-92 is not feasible.	Choose MMBT557LT1G for automated SMT assembly; BC557B,126 remains optimal for prototyping, repair, or through-hole production.

Compared with BC557C,126 and MMBT557LT1G, BC557B,126 provides verified B-grade h_FE consistency in legacy TO-92 form factor, balancing gain predictability, thermal performance (250 K/W), and hand-soldering accessibility-making it ideal for education, service, and low-volume industrial control boards.

Availability

BC557B,126 is available at Aetrix Electronics and suitable for audio pre-amplifiers, microcontroller GPIO level shifters, relay drivers, and LED current sink switches requiring stable component supply and long-term obsolescence resilience.

Supply support for BC557B,126 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

NXP Semiconductors is a global semiconductor company headquartered in Eindhoven, Netherlands, specializing in secure connectivity solutions for automotive, industrial, and consumer applications.

The BC557B,126 belongs to NXP's legacy general-purpose transistor product line, designed for cost-sensitive, reliability-critical analog and digital interface functions in industrial controls, instrumentation, and educational electronics.

FAQ

What is the maximum collector-emitter voltage rating for BC557B,126?

The BC557B,126 has a maximum collector-emitter voltage (V_CEO) rating of −45 V under open-base conditions. This value is specified in the Absolute Maximum Ratings table of the official NXP datasheet and defines the upper limit for safe DC operation without risk of junction breakdown. Exceeding this voltage may cause permanent device failure. The BC557B,126 must not be used in circuits where V_CE could transiently exceed −45 V, even briefly.

Is BC557B,126 pin-compatible with BC547?

No, BC557B,126 is not pin-compatible with BC547. While both are TO-92 packaged transistors, BC557B,126 is a PNP device with pinout E-B-C (pins 1–2–3), whereas BC547 is an NPN transistor with pinout E-B-C reversed in many common variants (e.g., BC547C uses C-B-E). Using BC557B,126 as a direct replacement for BC547 without circuit modification will result in non-functional or damaged operation due to polarity mismatch and inverted pin mapping.

What is the h_FE range for BC557B,126 at I_C = −2 mA?

The BC557B,126 has a DC current gain (h_FE) range of 220 to 475 when tested at I_C = −2 mA and V_CE = −5 V, as confirmed in the Characteristics section of the NXP datasheet. This B-grade binning distinguishes it from BC557A (125–250) and BC557C (420–800), ensuring consistent gain behavior for reliable base resistor design in amplification and switching applications.

Can BC557B,126 be used in surface-mount designs?

No, BC557B,126 is not suitable for surface-mount designs because it is packaged exclusively in the through-hole TO-92 (SOT54) format. For SMT implementations, engineers should select functionally comparable alternatives such as MMBT557LT1G (SOT-23) or PZT557 (SOT-223), which share identical electrical specifications but differ in package type, thermal profile, and reflow compatibility. BC557B,126 requires wave or hand soldering.

What is the thermal resistance from junction to ambient for BC557B,126?

The thermal resistance from junction to ambient (R_th(j-a)) for BC557B,126 is 250 K/W when mounted on a standard FR4 printed-circuit board, as stated in the Thermal Characteristics section of the NXP datasheet. This value assumes natural convection cooling and defines how much temperature rise occurs per milliwatt of power dissipated-e.g., at 300 mW dissipation, junction temperature rises ~75 °C above ambient. Derating is required above 25 °C ambient.

BC557B,126 Specifications

Product attributes: Attribute value

Manufacturer:: NXP Semiconductors

Series:: -

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

Packaging:: Tape & Box (TB)

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:: 220 @ 2mA, 5V

Power - Max:: 500 mW

Frequency - Transition:: 100MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

BC557B,126 FAQ

1.How can I place an order for BC557B,126 through Aetrix?

Please submit a Request for Quotation (RFQ) for BC557B,126 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 BC557B,126 reliable?

The price and inventory of BC557B,126 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC557B,126 is usually 5 days.

3.What payment methods are accepted for BC557B,126?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC557B,126 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC557B,126?

BC557B,126 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC557B,126 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 BC557B,126?

For technical support, including BC557B,126 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC557B,126 requirements.

6.How does Aetrix verify that BC557B,126 is sourced from the original manufacturer or authorized distributors?

All BC557B,126 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 BC557B,126 meets industry standards.

7.What is the process for return or replacement of BC557B,126?

All BC557B,126 units undergo pre-shipment inspection (PSI). If there is an issue with BC557B,126, 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 BC557B,126 part is unused and in its original packaging.

Return procedure for BC557B,126:

1.Submit a request within 90 days.

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

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