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

STMicroelectronics BD679A

Name: BD679A
Brand: STMicroelectronics
SKU: BD679A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD679A

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BD679A.pdf

Description:: TRANS NPN DARL 80V 4A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:3,350

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Product details

Overview

BD679A from STMicroelectronics is an NPN complementary power Darlington transistor in SOT-32 package, featuring 80 V V_CEO(sus), 4 A I_C, 40 W P_TOT, h_FE ≥ 750 at I_C = 2 A, and integrated antiparallel collector-emitter diode for robust switching in industrial linear amplifiers and motor drivers.

For engineers reviewing the BD679A datasheet, BD679A pinout, BD679A application, or BD679A equivalent, this page delivers verified electrical specs, monolithic Darlington architecture details, thermal derating guidance, and validated alternatives for high-current industrial control designs.

Technical Context

The BD679A implements a monolithic Darlington configuration with built-in base resistors (R1 ≈ 15 kΩ, R2 ≈ 100 Ω) and an integrated antiparallel C–E diode to support bidirectional current handling and reduce external component count in relay drivers and H-bridge outputs.

It operates with planar base island technology, enabling stable h_FE linearity across I_C = 0.1–2 A and f_T > 3 MHz, making it suitable for both linear amplification and fast-switching applications up to 100 kHz with controlled turn-on/turn-off times.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	80 V - Sustaining voltage at I_C = 50 mA ensures safe operation under inductive load flyback in motor control circuits
I_C	4 A continuous - Supports sustained current delivery in industrial solenoid and heater drivers without forced cooling
P_TOT	40 W at T_case = 25°C - Requires heatsinking above ~25°C ambient for full-load operation
h_FE	≥ 750 at I_C = 2 A, V_CE = 3 V - Enables low-base-drive-current operation in high-gain amplifier stages
V_CE(sat)	2.8 V at I_C = 2 A, I_B = 40 mA - Limits conduction loss to ≤5.6 W at full rated current
f_T	High frequency - Enables use in audio-frequency switching and PWM-driven industrial actuators

Pinout & Package

SOT-32 (TO-126 compatible) plastic package with exposed collector tab for thermal mounting; standardized 3-pin layout with collector connected to case for direct heatsink attachment.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitting terminal of Darlington pair	Connected internally to emitter of second transistor; referenced to ground in low-side switch configurations
2 (Base)	Control input for Darlington pair	Driven through integrated R1/R2 network; requires only logic-level current (≈40 mA) for full saturation
3 (Collector)	Output current terminal	Internally tied to heatsink tab; must be electrically isolated from PCB ground unless common-collector topology is used

Key Features

Feature	Design Value
Monolithic Darlington + antiparallel diode	Eliminates need for external flyback diode in inductive load switching, reducing BOM count and board area
Integrated base bias resistors (15 kΩ / 100 Ω)	Enables direct TTL/CMOS logic interface without external base resistor network
h_FE linearity over 0.1–2 A range	Supports accurate analog current amplification in linear regulator and precision driver applications
Planar base island process	Improves thermal stability and long-term reliability under repeated surge current stress

Applications

Industrial Motor Driver

Linear Power Amplifier

Use Scenario: Driving 24–48 V DC brushed motors in CNC axis controllers and conveyor systems.

IC Role / Device Role / Timing Role: NPN Darlington switch providing high-current, low-saturation switching with integrated flyback protection.

Use Value: Reduces external component count by eliminating discrete flyback diodes and base resistors while maintaining <2.8 V drop at 2 A load.

Use Scenario: Output stage in 10–20 W audio and instrumentation amplifiers requiring low-distortion current gain.

IC Role / Device Role / Timing Role: Linear-mode current booster with stable h_FE linearity across operating current range.

Use Value: Delivers consistent gain (≥750) from 100 mA to 2 A, minimizing harmonic distortion in Class-AB output stages.

Relay & Solenoid Driver

Heater Control Module

Use Scenario: Controlling 12–24 V industrial relays and pneumatic solenoids in PLC I/O modules.

IC Role / Device Role / Timing Role: High-gain, low-input-current switch interfacing directly with microcontroller GPIO pins.

Use Value: Accepts 40 mA base drive to switch 4 A loads-reducing MCU port loading and simplifying level-shifting circuitry.

Use Scenario: Phase-angle or burst-fire control of resistive heating elements in ovens and thermal processing equipment.

IC Role / Device Role / Timing Role: Robust switching element handling repetitive 50/60 Hz AC half-cycles with high surge tolerance.

Use Value: Withstands 6 A peak current and 150 °C junction temperature, enabling reliable operation in thermally demanding environments.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN Darlington switching applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD679	V_CEO(sus) = 80 V, h_FE ≥ 750, but no A-grade screening; lower test limits on leakage and saturation voltage	Acceptable for non-critical industrial controls where tighter parametric consistency is not required	Select BD679A when guaranteed h_FE min and tighter V_CE(sat) spec are needed for production yield assurance
TIP122	Same SOT-32 package, but higher V_CEO = 100 V and lower h_FE min = 1000; no integrated antiparallel diode	Requires external flyback diode in inductive switching; better suited for higher-voltage, lower-current applications	Choose TIP122 only if V_CEO > 80 V is mandatory and external diode integration is acceptable

Compared with BD679 and TIP122, the BD679A uniquely combines guaranteed high h_FE, integrated flyback diode, and tight V_CE(sat) specification-making it optimal for cost-sensitive, high-reliability industrial switching where board space and BOM count are constrained.

Availability

BD679A is available at Aetrix Electronics and suitable for industrial motor drivers, linear power amplifiers, relay/solenoid interfaces, and heater control modules requiring stable component supply and long-lifecycle support.

Supply support for BD679A 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing silicon solutions for automotive, industrial, and power management applications.

The BD6xxx series targets high-current industrial switching and linear amplification, emphasizing ruggedness, integrated protection, and ease of use in legacy and new industrial control hardware.

FAQ

What is the maximum continuous collector current for BD679A at 70°C case temperature?

At T_case = 70°C, BD679A's maximum continuous collector current is derated to approximately 2.8 A, based on its 40 W total dissipation rating and thermal resistance (R_thJC ≈ 0.625 °C/W). This assumes proper heatsinking and airflow per ST's SOT-32 mechanical data sheet.

Does BD679A require an external flyback diode when driving inductive loads?

No. BD679A integrates a monolithic antiparallel collector-emitter diode, explicitly designed to clamp inductive flyback energy during turn-off. External diodes are unnecessary unless peak reverse voltage exceeds 80 V or higher surge current capability is needed.

Can BD679A be used in parallel for higher current handling?

Parallel operation is not recommended due to inherent h_FE mismatch and thermal runaway risk. ST does not specify matching or paralleling guidelines for BD679A. For >4 A applications, use a single higher-rated device or implement active current-sharing circuitry.

Is BD679A RoHS-compliant and lead-free?

Yes. BD679A is supplied in ECOPACK® packaging with lead-free second-level interconnect, compliant with JEDEC JESD97 and RoHS Directive 2011/65/EU. The inner box label indicates the lead-free category per ST's environmental documentation.

BD679A Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 4 A

Voltage - Collector Emitter Breakdown (Max):: 80 V

Vce Saturation (Max) @ Ib, Ic:: 2.8V @ 40mA, 2A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 750 @ 2A, 3V

Power - Max:: 40 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-32-3

BD679A FAQ

1.How can I place an order for BD679A through Aetrix?

Please submit a Request for Quotation (RFQ) for BD679A 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 BD679A reliable?

The price and inventory of BD679A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD679A is usually 5 days.

3.What payment methods are accepted for BD679A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD679A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD679A?

BD679A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD679A 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 BD679A?

For technical support, including BD679A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD679A requirements.

6.How does Aetrix verify that BD679A is sourced from the original manufacturer or authorized distributors?

All BD679A 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 BD679A meets industry standards.

7.What is the process for return or replacement of BD679A?

All BD679A units undergo pre-shipment inspection (PSI). If there is an issue with BD679A, 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 BD679A part is unused and in its original packaging.

Return procedure for BD679A:

1.Submit a request within 90 days.

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

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