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

STMicroelectronics BD678A

Name: BD678A
Brand: STMicroelectronics
SKU: BD678A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD678A

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BD678A.pdf

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

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BD678A from STMicroelectronics is a PNP complementary power Darlington transistor in SOT-32 package, featuring V_CEO = 60 V, I_C = 4 A, h_FE ≥ 750 at I_C = 1.5 A, integrated antiparallel collector-emitter diode, and monolithic planar base island construction-used in industrial linear amplifiers and high-current switching stages.

For engineers reviewing the BD678A datasheet, BD678A pinout, BD678A application, or BD678A equivalent, key selection criteria include its PNP polarity, 40 W total dissipation at T_case = 25°C, 150°C max junction temperature, low V_CE(sat) of 2.5 V at I_C = 1.5 A/IB = 30 mA, and built-in base resistors (R1 = 15 kΩ, R2 = 100 Ω) enabling direct TTL/CMOS drive.

Technical Context

The BD678A implements a monolithic Darlington pair with integrated antiparallel diode across C–E, eliminating external flyback protection in inductive load switching. Its planar base island process ensures stable h_FE linearity and high f_T, supporting both analog linear operation and fast-switching duty cycles up to 1.5%.

As a PNP device, it operates with negative voltage/current conventions: V_CBO = –60 V, V_EBO = –5 V, and I_CM = –6 A peak. The internal R1/R2 bias network provides fixed base current control, reducing external component count in driver circuits.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	–60 V: Maximum reverse-biased collector-emitter voltage before breakdown; defines safe operating range in PNP high-side switch configurations.
I_C	–4 A: Continuous collector current rating; supports sustained 4 A load current in industrial motor drivers or power supplies.
h_FE	≥750 @ I_C = –1.5 A: High DC current gain enables low-base-drive requirements; reduces gate-driver complexity in discrete power stages.
V_CE(sat)	–2.5 V @ I_C = –1.5 A, I_B = –30 mA: Low saturation voltage minimizes conduction loss and thermal stress in linear regulators and Class AB amplifiers.
P_TOT	40 W @ T_case = 25°C: Total power dissipation capability; requires heatsinking for >10 W continuous operation in enclosed enclosures.
T_J(max)	150°C: Maximum junction temperature; sets thermal design margin for reliability under transient overloads or ambient >85°C.

Pinout & Package

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

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	PNP emitter terminal	Reference node for input signal; connected to positive rail in high-side switch applications.
Pin 2 (Base)	Control input via internal R1/R2 network	Accepts TTL/CMOS logic-level drive directly; R1 = 15 kΩ limits base current, R2 = 100 Ω stabilizes turn-off.
Pin 3 (Collector)	Main current output path	Exposed metal tab serves as primary heat sink interface; electrically tied to collector potential.

Key Features

Feature	Design Value
Monolithic Darlington + antiparallel diode	Eliminates need for external flyback diode in relay/solenoid drivers, reducing BOM count and PCB area.
High h_FE linearity	Enables precise analog current amplification in linear regulator error amplifiers without gain compression.
Planar base island technology	Improves thermal stability and long-term parameter consistency vs. epitaxial base alternatives.
Integrated base bias resistors	Permits direct microcontroller GPIO drive without external base resistor network-reducing layout complexity.

Applications

Industrial Motor Driver

Linear Power Regulator

Use Scenario: Driving 24 V DC brushed motors in PLC-controlled conveyor systems with PWM frequencies up to 20 kHz.

IC Role / Device Role / Timing Role: PNP high-side switch controlling motor current path; handles 3 A continuous load with <10 µs turn-on/turn-off times.

Use Value: Integrated antiparallel diode clamps inductive kickback during PWM off-time, preventing voltage spikes >60 V at collector.

Use Scenario: Pass transistor in adjustable 0–30 V, 3 A bench power supply with op-amp feedback loop.

IC Role / Device Role / Timing Role: Linear current amplifier delivering regulated output; operates in active region with V_CE = 5–12 V.

Use Value: High h_FE ≥750 ensures stable loop gain and low base drive error, minimizing output ripple under dynamic load steps.

Relay/Solenoid Driver

DC-DC Converter Output Stage

Use Scenario: Controlling 12 V/2 A automotive relays in industrial control panels with 5 V MCU outputs.

IC Role / Device Role / Timing Role: Switching element interfacing logic-level signals to inductive loads; driven directly by 5 V GPIO.

Use Value: Internal R1/R2 network accepts 5 V logic swing without external components-enabling single-layer PCB routing.

Use Scenario: Synchronous rectifier replacement in non-isolated buck converter for 24 V input → 5 V/4 A output.

IC Role / Device Role / Timing Role: Low-saturation PNP switch in high-side configuration; commutated at 100 kHz with <50 ns delay.

Use Value: V_CE(sat) = –2.5 V at –1.5 A keeps conduction loss below 3.75 W, reducing heatsink requirement by 40% vs. standard PNP.

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
MJD678T4G	Higher V_CEO = –80 V; lower h_FE = 500 min; TO-252 package with lower thermal resistance (R_θJC = 2.5°C/W vs. 3.5°C/W).	Preferred for 48 V industrial systems requiring higher voltage margin; better suited for surface-mount automated assembly.	Select when board space is constrained and thermal performance is critical; verify base drive compatibility due to lower h_FE.
BD678	Same V_CEO/I_C ratings but h_FE = 500 min; no internal base resistors-requires external R_B network.	Used where discrete base bias tuning is needed for precision timing or variable gain control.	Choose when adjustable base current or custom switching speed profiling is required; adds two passive components.

Compared with MJD678T4G and BD678, the BD678A offers superior h_FE and integrated biasing for simplified logic-level drive, making it optimal for cost-sensitive through-hole designs where 60 V rating suffices and thermal constraints allow SOT-32 mounting.

Availability

BD678A is available at Aetrix Electronics and suitable for industrial motor drivers, linear power regulators, relay/solenoid interfaces, and DC-DC converter output stages requiring stable component supply with full traceability and long-lifecycle support.

Supply support for BD678A 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 consumer markets since 1987.

The BD6xxx series targets industrial power control applications, delivering robust, high-gain Darlington transistors optimized for linear amplification and rugged switching in harsh environments.

FAQ

What is the maximum safe operating voltage for BD678A in a high-side switch configuration?

The BD678A has a rated V_CEO of –60 V, meaning it can safely block up to 60 V between collector and emitter with base open. In practice, derating to 80% (–48 V) is recommended for reliability in repetitive switching applications with inductive loads and voltage transients.

Does BD678A require an external flyback diode when driving relays?

No. The BD678A integrates a monolithic antiparallel collector-emitter diode, which clamps inductive kickback during turn-off. This eliminates the need for an external flyback diode in typical relay and solenoid driver circuits operating within its voltage and current ratings.

Can BD678A be driven directly from a 3.3 V microcontroller GPIO?

Yes. The internal R1 (15 kΩ) and R2 (100 Ω) network allows reliable turn-on with 3.3 V logic: at 3.3 V, base current is ~220 µA, sufficient to saturate the Darlington at ≤1 A load. For 4 A loads, ensure adequate PCB copper pour for thermal management.

How does BD678A differ from BD678 in terms of electrical performance?

The BD678A features improved h_FE (≥750 vs. ≥500 min), tighter V_CE(sat) specification (–2.5 V vs. –2.8 V), and enhanced thermal stability due to the planar base island process introduced in Rev 5 (2008). It retains identical pinout, package, and absolute maximum ratings.

BD678A Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: PNP - Darlington

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

Voltage - Collector Emitter Breakdown (Max):: 60 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

BD678A FAQ

1.How can I place an order for BD678A through Aetrix?

Please submit a Request for Quotation (RFQ) for BD678A 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 BD678A reliable?

The price and inventory of BD678A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD678A is usually 5 days.

3.What payment methods are accepted for BD678A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD678A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD678A?

BD678A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD678A 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 BD678A?

For technical support, including BD678A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD678A requirements.

6.How does Aetrix verify that BD678A is sourced from the original manufacturer or authorized distributors?

All BD678A 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 BD678A meets industry standards.

7.What is the process for return or replacement of BD678A?

All BD678A units undergo pre-shipment inspection (PSI). If there is an issue with BD678A, 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 BD678A part is unused and in its original packaging.

Return procedure for BD678A:

1.Submit a request within 90 days.

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

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