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

STMicroelectronics BD678

Name: BD678
Brand: STMicroelectronics
SKU: BD678
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD678

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BD678.pdf

Description:: TRANS PNP DARL 60V 4A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:3,834

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Product details

Overview

BD678 from STMicroelectronics is a PNP complementary power Darlington transistor in SOT-32 package, featuring 60 V V_CEO, 4 A I_C, 40 W P_TOT, h_FE ≥ 750 at I_C = 1.5 A, and integrated antiparallel collector-emitter diode-used in industrial linear amplifiers and high-current switching stages.

For engineers reviewing the BD678 datasheet, BD678 pinout, BD678 application, or BD678 equivalent, this page delivers verified electrical specs, monolithic Darlington architecture details, thermal derating guidance, and validated alternatives for high-gain, medium-voltage PNP switching designs.

Technical Context

The BD678 implements a monolithic Darlington configuration with built-in antiparallel C–E diode, enabling bidirectional current handling without external clamping. Its planar base island process ensures stable h_FE linearity and high f_T, critical for analog feedback loops and pulse-width modulated motor drives.

Rated for T_J up to 150 °C and V_CBO = 60 V, it operates under continuous DC or pulsed (300 ms, ≥1.5% duty) conditions. The integrated diode supports inductive load commutation, reducing external component count in relay and solenoid drivers.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - Maximum safe collector-emitter voltage with base open; defines upper rail limit in linear regulators and switch-mode output stages.
I_C	4 A - Continuous collector current rating; supports 3–5 A peak loads in industrial motor control with appropriate heatsinking.
h_FE	≥750 @ I_C = 1.5 A - High DC current gain enables low-base-drive requirements, reducing driver-stage complexity and power loss.
V_CE(sat)	2.5 V @ I_C = 1.5 A, I_B = 30 mA - Low saturation voltage minimizes conduction loss in high-current switching applications.
P_TOT	40 W @ T_case = 25 °C - Total dissipation capability; requires thermal interface design for >15 W operation in ambient >50 °C.
f_T	High - Enables stable operation up to several hundred kHz in Class AB audio output stages and SMPS error amplifiers.

Pinout & Package

SOT-32 (TO-126 compatible) three-terminal plastic package with exposed collector tab for thermal mounting. Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (tab).

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	Current sink terminal	Connected to system ground or negative rail; carries full load current in common-emitter configurations.
Pin 2 (Base)	Control input	Receives low-current drive signal; base resistor network must limit I_B ≤ 0.1 A per absolute max rating.
Pin 3 (Collector / Tab)	Main current path & thermal interface	Electrically and thermally connected to heatsink; requires insulating washer if mounted to grounded metal chassis.

Key Features

Feature	Design Value
Monolithic Darlington structure	Single-die integration eliminates inter-device parameter mismatch and improves thermal coupling between driver and output transistors.
Integrated antiparallel C–E diode	Eliminates need for external flyback diode in inductive load switching, reducing BOM count and PCB area in relay/solenoid drivers.
Good h_FE linearity	Enables precise analog current mirroring and low-distortion linear amplification in industrial sensor signal conditioning circuits.
Planar base island technology	Provides consistent breakdown voltage and improved ruggedness against secondary breakdown during transient overloads.

Applications

Industrial Linear Amplifier

DC Motor H-Bridge Driver

Use Scenario: High-fidelity current source for precision temperature controller output stage.

IC Role / Device Role / Timing Role: PNP Darlington output device delivering 2–3 A continuous current into resistive heating element.

Use Value: High h_FE reduces base drive burden on op-amp feedback loop; integrated diode prevents latch-up during thermal cycling.

Use Scenario: Upper-leg switch in 24 V DC brushed motor H-bridge for factory automation actuator.

IC Role / Device Role / Timing Role: High-side PNP switch controlling motor direction and braking via PWM.

Use Value: 60 V V_CEO accommodates back-EMF spikes; 40 W dissipation supports 100% duty cycle at 2 A with forced-air cooling.

Relay/Solenoid Driver

Linear Voltage Regulator Pass Element

Use Scenario: Driving 48 V/2 A industrial relay coil with fast turn-off and surge suppression.

IC Role / Device Role / Timing Role: Switching transistor with integrated flyback path for coil energy recirculation.

Use Value: Built-in antiparallel diode ensures <5 µs turn-off delay and eliminates external diode selection/validation effort.

Use Scenario: Series pass element in adjustable 0–30 V, 3 A bench power supply.

IC Role / Device Role / Timing Role: Power transistor regulating output voltage under variable load and line conditions.

Use Value: Stable h_FE linearity across I_C range enables accurate current limiting and smooth foldback behavior.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD678A	Higher V_CEO = 80 V, higher h_FE ≥ 750 @ I_C = 2 A, V_CE(sat) = 2.8 V	Supports wider input voltage range in SMPS front-end and higher bus voltages in servo drives	Select when operating above 60 V or requiring tighter h_FE tolerance at elevated current.
MJD47	Lower V_CEO = 40 V, lower h_FE = 250–750, no integrated diode	Requires external flyback diode; limited to ≤36 V systems with moderate gain stability needs	Choose only for cost-sensitive, low-voltage (<40 V), non-critical linear applications where diode can be added.

Compared with BD678, BD678A offers extended voltage headroom and higher current gain at 2 A, while MJD47 trades integration and ruggedness for lower cost and smaller footprint-making BD678 the optimal balance of performance, protection, and manufacturability for 48–60 V industrial controls.

Availability

BD678 is available at Aetrix Electronics and suitable for industrial linear amplifiers, DC motor H-bridge drivers, relay/solenoid drivers, and linear voltage regulator pass elements requiring stable component supply and long-term obsolescence management.

Supply support for BD678 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 analog, digital, and mixed-signal ICs, discrete devices, and MEMS sensors for industrial, automotive, and consumer markets.

The BD6xxx series targets industrial power control, delivering robust, high-gain Darlington transistors optimized for linear regulation, switching, and inductive load driving in harsh environments.

FAQ

What is the maximum safe junction temperature for BD678?

The BD678 has a maximum operating junction temperature (T_J) of 150 °C, as specified in its Absolute Maximum Ratings table. Operation beyond this limit risks permanent degradation of h_FE and increased leakage. Thermal design must ensure case-to-ambient resistance remains below 3.125 °C/W when dissipating 40 W at 25 °C ambient.

Does BD678 require an external flyback diode when driving inductive loads?

No. The BD678 integrates a monolithic antiparallel collector-emitter diode, explicitly designed to clamp inductive kickback during turn-off. This eliminates the need for an external diode in standard relay, solenoid, and DC motor applications-reducing bill-of-materials and layout complexity.

How does BD678 differ from BD677 in circuit implementation?

BD678 is the PNP complement to the NPN BD677. They share identical package (SOT-32), power rating (40 W), and gain characteristics (h_FE ≥ 750), but opposite polarity: BD678 sinks current from V_CC to load, while BD677 sources current from load to ground. They are used together in push-pull or complementary symmetry amplifier stages.

Can BD678 be used in Class AB audio output stages?

Yes-its high h_FE linearity, low V_CE(sat), and stable f_T make it suitable for medium-power Class AB audio output stages up to ~20 W. However, thermal management is critical: the device must be mounted on a heatsink capable of maintaining T_case ≤ 25 °C under full bias to sustain rated P_TOT and avoid crossover distortion.

BD678 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Active

Transistor Type:: PNP - Darlington

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

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 2.5V @ 30mA, 1.5A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 750 @ 1.5A, 3V

Power - Max:: 40 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-32-3

BD678 FAQ

1.How can I place an order for BD678 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD678 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 BD678 reliable?

The price and inventory of BD678 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD678 is usually 5 days.

3.What payment methods are accepted for BD678?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD678 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD678?

BD678 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD678 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 BD678?

For technical support, including BD678 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD678 requirements.

6.How does Aetrix verify that BD678 is sourced from the original manufacturer or authorized distributors?

All BD678 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 BD678 meets industry standards.

7.What is the process for return or replacement of BD678?

All BD678 units undergo pre-shipment inspection (PSI). If there is an issue with BD678, 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 BD678 part is unused and in its original packaging.

Return procedure for BD678:

1.Submit a request within 90 days.

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

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