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

onsemi BC857ALT1

Name: BC857ALT1
Brand: onsemi
SKU: BC857ALT1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC857ALT1

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: -

Datasheet:: BC857ALT1.pdf

Description:: TRANS PNP GP 45V 100MA SOT-23

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BC857ALT1 from onsemi is a PNP silicon general-purpose transistor in SOT-23 package, rated for −45 V V_CEO, −50 V V_CBO, −5.0 V V_EBO, −100 mA I_C continuous, and featuring h_FE = 125–250 (at I_C = −10 mA, V_CE = −5.0 V). It operates across −55°C to +150°C and supports low-voltage switching and signal amplification in automotive and industrial control circuits.

For engineers reviewing the BC857ALT1 datasheet, pinout, applications, or equivalent options, key selection criteria include its AEC-Q101 qualification, Pb-free RoHS-compliant SOT-23 footprint, verified DC current gain range, saturation voltage performance at −10 mA/−0.5 mA bias, and thermal resistance of 556°C/W on FR-5 board.

Technical Context

This PNP bipolar junction transistor uses epitaxial planar die construction with base-emitter and collector-base junctions optimized for stable DC gain and fast switching. Its electrical behavior is defined by fixed junction temperature limits (T_J = −55°C to +150°C), specified breakdown voltages under controlled test conditions (e.g., V_(BR)CEO = −45 V at I_C = −10 mA), and normalized h_FE curves across collector current and temperature.

Thermal performance is characterized via transient thermal impedance (Z_JC(t)) and steady-state R_JA = 556°C/W (FR-5) or 417°C/W (alumina), enabling accurate junction temperature estimation in pulsed or continuous operation. Switching parameters-t_d = 35 ns, t_r = 25 ns, t_s = 310 ns, t_f = 40 ns-are measured at V_CC = −3.0 V, I_C = −10 mA, I_E = −1 mA.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−45 V - Maximum allowable collector-emitter voltage before breakdown under open-base condition; defines safe operating voltage headroom in PNP switch configurations.
I_C (continuous)	−100 mA - Continuous collector current rating; sets upper limit for steady-state load drive capability without thermal derating.
h_FE range	125–250 - DC current gain at I_C = −10 mA, V_CE = −5.0 V; determines required base drive current for target collector current in linear or saturated operation.
V_CE(sat)	−0.3 V (max) at I_C = −10 mA, I_B = −0.5 mA - Saturation voltage drop; directly impacts power loss and voltage margin in low-side PNP switch applications.
f_T	100 MHz - Current-gain bandwidth product; indicates usable frequency limit for small-signal amplification or RF switching up to ~10 MHz with gain >1.
R_JA	556°C/W - Junction-to-ambient thermal resistance on FR-5 board; used to calculate ΔT_J = P_D × R_JA for thermal design compliance.

Pinout & Package

SOT-23 (TO-236) package: 2.90 mm × 1.30 mm × 1.00 mm body, 1.90 mm lead pitch, surface-mount compatible, JEDEC-standard footprint.

Pin/Terminal	Circuit Role	Design Meaning
1	Base	Control terminal; forward-biased with negative voltage relative to emitter to turn on PNP conduction path between collector and emitter.
2	Emitter	Current source terminal; connected to higher potential (e.g., V_CC) in common-emitter switch configuration; carries full load current.
3	Collector	Current sink terminal; delivers load current to ground or lower-potential node; voltage swing limited by V_CEO and V_CBO ratings.

Key Features

Feature	Design Value
AEC-Q101 qualified	Validated for automotive-grade reliability including temperature cycling, humidity testing, and mechanical shock per AEC specification; suitable for engine control, body electronics, and ADAS subsystems.
Pb-free, RoHS-compliant	Meets EU RoHS Directive 2011/65/EU and halogen-free/BFR-free requirements; enables compliance with global environmental regulations and end-of-life processing standards.
Low V_CE(sat)	−0.3 V max at I_C/I_B = 10 ensures <10 mW conduction loss at 10 mA load, reducing heat generation in space-constrained PCB layouts.
High f_T	100 MHz bandwidth supports stable small-signal amplification up to audio frequencies and fast digital switching with sub-100 ns transition times.
Wide T_J range	−55°C to +150°C operation enables deployment in under-hood automotive environments, industrial motor drives, and outdoor power equipment.

Applications

Automotive Door Module Control	Industrial PLC Input Conditioning
Use Scenario: Driving LED status indicators and relays in door lock/unlock modules where supply rail is 12 V and microcontroller GPIOs operate at 3.3 V or 5 V. IC Role / Device Role / Timing Role: PNP level-shifting switch that interfaces low-voltage logic outputs to 12 V loads, providing inverted logic control with minimal external components. Use Value: Enables direct GPIO control of 12 V loads without optocouplers or dedicated level shifters; V_CEO = −45 V provides 3× safety margin over nominal 12 V system.	Use Scenario: Converting 24 V industrial sensor signals (NPN open-collector or dry contact) into clean 3.3 V logic levels for ARM-based PLC input processors. IC Role / Device Role / Timing Role: Signal conditioning amplifier and level translator in input stage, configured as common-emitter inverter with h_FE-stabilized bias network. Use Value: Delivers predictable 24 V → 3.3 V translation with <1 µs propagation delay; h_FE range allows robust bias design across production lots.
Consumer Appliance Power Sequencing	Medical Infusion Pump Motor Enable
Use Scenario: Enabling 5 V standby rails and 12 V main power supplies in smart washing machines and HVAC controllers using MCU-controlled sequencing logic. IC Role / Device Role / Timing Role: Low-side enable switch controlling gate drive for external N-channel MOSFETs or base drive for Darlington pairs in multi-rail power management. Use Value: −100 mA I_C rating supports driving multiple parallel MOSFET gates; SOT-23 footprint minimizes board area in dense power control sections.	Use Scenario: Safely enabling stepper motor drivers in Class II medical infusion pumps where isolation and fault tolerance are critical. IC Role / Device Role / Timing Role: Redundant enable path component in dual-redundant motor control architecture, operated in linear region for soft-start current limiting. Use Value: AEC-Q101 qualification and −55°C to +150°C T_J ensure long-term reliability under sterilization cycles and ambient temperature variations; V_CE(sat) stability reduces thermal drift during extended operation.

Automotive Door Module Control

Industrial PLC Input Conditioning

Use Scenario: Driving LED status indicators and relays in door lock/unlock modules where supply rail is 12 V and microcontroller GPIOs operate at 3.3 V or 5 V.

IC Role / Device Role / Timing Role: PNP level-shifting switch that interfaces low-voltage logic outputs to 12 V loads, providing inverted logic control with minimal external components.

Use Value: Enables direct GPIO control of 12 V loads without optocouplers or dedicated level shifters; V_CEO = −45 V provides 3× safety margin over nominal 12 V system.

Use Scenario: Converting 24 V industrial sensor signals (NPN open-collector or dry contact) into clean 3.3 V logic levels for ARM-based PLC input processors.

IC Role / Device Role / Timing Role: Signal conditioning amplifier and level translator in input stage, configured as common-emitter inverter with h_FE-stabilized bias network.

Use Value: Delivers predictable 24 V → 3.3 V translation with <1 µs propagation delay; h_FE range allows robust bias design across production lots.

Consumer Appliance Power Sequencing

Medical Infusion Pump Motor Enable

Use Scenario: Enabling 5 V standby rails and 12 V main power supplies in smart washing machines and HVAC controllers using MCU-controlled sequencing logic.

IC Role / Device Role / Timing Role: Low-side enable switch controlling gate drive for external N-channel MOSFETs or base drive for Darlington pairs in multi-rail power management.

Use Value: −100 mA I_C rating supports driving multiple parallel MOSFET gates; SOT-23 footprint minimizes board area in dense power control sections.

Use Scenario: Safely enabling stepper motor drivers in Class II medical infusion pumps where isolation and fault tolerance are critical.

IC Role / Device Role / Timing Role: Redundant enable path component in dual-redundant motor control architecture, operated in linear region for soft-start current limiting.

Use Value: AEC-Q101 qualification and −55°C to +150°C T_J ensure long-term reliability under sterilization cycles and ambient temperature variations; V_CE(sat) stability reduces thermal drift during extended operation.

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
BC857BLT1G	Higher h_FE range (220–475 at I_C = −10 mA); otherwise identical ratings, package, and pinout.	Better suited for low-base-drive applications such as high-gain preamplifiers or low-current switching where tighter h_FE control improves consistency.	Select BC857BLT1G when circuit requires guaranteed minimum h_FE ≥ 220; BC857ALT1 remains optimal for cost-sensitive designs needing only h_FE ≥ 125.
MMBT3906LT1G	Same SOT-23 package and PNP polarity, but lower V_CEO (−40 V), lower f_T (250 MHz typ but not guaranteed min), and non-AEC-Q101 qualified.	Used in commercial-grade consumer electronics where automotive qualification is unnecessary and −40 V rating suffices.	Choose MMBT3906LT1G for non-automotive cost-driven designs; BC857ALT1 is preferred where AEC-Q101 compliance, −45 V margin, or guaranteed h_FE min are mandatory.

Compared with BC857BLT1G and MMBT3906LT1G, BC857ALT1 offers the optimal balance of automotive qualification, guaranteed mid-range h_FE, and −45 V breakdown margin-making it ideal for industrial control and Tier-1 automotive subsystems where reliability and specification certainty outweigh maximum gain or lowest cost.

Availability

BC857ALT1 is available at Aetrix Electronics and suitable for automotive body electronics, industrial PLC input stages, and medical device power sequencing requiring stable component supply, long lifecycle support, and traceable sourcing.

Supply support for BC857ALT1 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 is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BC857ALT1 belongs to onsemi's BC856ALT1G Series of general-purpose PNP transistors designed for reliable, high-volume switching and amplification in space-constrained, thermally demanding environments.

FAQ

What is the maximum collector-emitter voltage rating for BC857ALT1?

The BC857ALT1 has a maximum collector-emitter voltage (V_CEO) rating of −45 V, tested at I_C = −10 mA with open base. This rating defines the absolute maximum reverse bias voltage the transistor can withstand in common-emitter configuration without breakdown, and must be respected in all operating conditions-including transient spikes-to ensure long-term reliability.

Is BC857ALT1 qualified for automotive applications?

Yes, BC857ALT1 is AEC-Q101 qualified and PPAP capable, as confirmed in the official onsemi datasheet. The "S" prefix variant (e.g., SBC857ALT1G*) is explicitly designated for automotive use with unique site and control change requirements, while the standard BC857ALT1G meets the same reliability and stress-test standards required for under-hood and chassis-mounted electronics.

What is the DC current gain (h_FE) range of BC857ALT1 at typical operating conditions?

The BC857ALT1 exhibits a DC current gain (h_FE) range of 125 to 250 when measured at I_C = −10 mA and V_CE = −5.0 V, TA = 25°C. This range is guaranteed per datasheet specifications and applies to the "A" grade variant; it enables predictable base current calculation for saturation or linear-mode biasing in production designs.

Does BC857ALT1 have a Pb-free and RoHS-compliant package?

Yes, BC857ALT1 is supplied in a Pb-free, halogen-free/BFR-free SOT-23 package and is fully RoHS compliant per EU Directive 2011/65/EU. The "G" suffix in part numbers like BC857ALT1G explicitly denotes the Pb-free version, and the device meets JEDEC J-STD-020 moisture sensitivity level (MSL) requirements for surface-mount assembly.

What are the thermal characteristics of BC857ALT1 on a standard FR-5 PCB?

On an FR-5 board, BC857ALT1 has a total device dissipation (P_D) of 225 mW at T_A = 25°C, derating by 1.8 mW/°C above that temperature. Its junction-to-ambient thermal resistance (R_JA) is 556°C/W, meaning a 100 mW power dissipation results in a 55.6°C junction-to-ambient temperature rise-critical for thermal margin analysis in sealed enclosures or high-ambient environments.

BC857ALT1 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: -

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: -

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

Voltage - Collector Emitter Breakdown (Max):: -

Vce Saturation (Max) @ Ib, Ic:: -

Current - Collector Cutoff (Max):: -

DC Current Gain (hFE) (Min) @ Ic, Vce:: -

Power - Max:: -

Frequency - Transition:: -

Operating Temperature:: -

Grade:: -

Qualification:: -

Mounting Type:: -

Supplier Device Package:: -

BC857ALT1 FAQ

1.How can I place an order for BC857ALT1 through Aetrix?

Please submit a Request for Quotation (RFQ) for BC857ALT1 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 BC857ALT1 reliable?

The price and inventory of BC857ALT1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC857ALT1 is usually 5 days.

3.What payment methods are accepted for BC857ALT1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC857ALT1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC857ALT1?

BC857ALT1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC857ALT1 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 BC857ALT1?

For technical support, including BC857ALT1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC857ALT1 requirements.

6.How does Aetrix verify that BC857ALT1 is sourced from the original manufacturer or authorized distributors?

All BC857ALT1 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 BC857ALT1 meets industry standards.

7.What is the process for return or replacement of BC857ALT1?

All BC857ALT1 units undergo pre-shipment inspection (PSI). If there is an issue with BC857ALT1, 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 BC857ALT1 part is unused and in its original packaging.

Return procedure for BC857ALT1:

1.Submit a request within 90 days.

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

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