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

STMicroelectronics BD677A

Name: BD677A
Brand: STMicroelectronics
SKU: BD677A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD677A

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BD677A.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:1,528

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Product details

Overview

BD677A from STMicroelectronics is an NPN complementary power Darlington transistor in SOT-32 (TO-126) package, featuring monolithic Darlington configuration with integrated antiparallel collector-emitter diode, 80 V V_CEO, 4 A I_C, 40 W P_TOT, and h_FE ≥ 750 at I_C = 2 A. It is used in linear and switching industrial equipment requiring high-current gain and robust thermal handling.

For engineers reviewing the BD677A datasheet, BD677A pinout, BD677A application, or BD677A equivalent, key selection factors include its 80 V collector-emitter sustaining voltage, 2.8 V V_CE(sat) at 2 A/40 mA drive, integrated clamping diode, planar base island process, and suitability for industrial motor control and power supply output stages.

Technical Context

The BD677A implements a monolithic Darlington pair with built-in antiparallel C–E diode to suppress inductive kickback during switching. Its planar base island technology ensures stable h_FE linearity and high f_T, supporting reliable operation up to 150 °C junction temperature.

It operates as a high-gain, medium-voltage NPN switch with fixed internal base bias resistors (R1 ≈ 15 kΩ, R2 ≈ 100 Ω), enabling direct TTL/CMOS-compatible drive without external base resistors while maintaining low saturation voltage under 2 A load.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	80 V - Maximum safe collector-emitter voltage with base open; defines usable rail voltage headroom in linear regulators and motor drivers.
I_C	4 A - Continuous collector current rating; supports sustained 3–5 A peak loads in industrial relay drivers and power amplifiers.
h_FE	≥750 @ I_C=2 A - High DC current gain reduces required base drive current, easing microcontroller interface design.
V_CE(sat)	2.8 V @ I_C=2 A, I_B=40 mA - Low saturation voltage minimizes conduction loss and heat generation in switching applications.
P_TOT	40 W @ T_case=25°C - Total power dissipation capability enables use with modest heatsinking in 25–50 W output stages.
f_T	High - Enables stable operation in audio-frequency switching (≤100 kHz) and analog amplifier feedback loops.

Pinout & Package

SOT-32 (TO-126) plastic package with standard 3-pin vertical mounting footprint, metal tab connected to collector for heatsink attachment and thermal management.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitting terminal of Darlington pair	Reference node for load return path; internally tied to emitter of second transistor in cascade.
2 (Base)	Input control terminal	Drives first transistor's base; includes integrated R1/R2 bias network for simplified logic-level drive.
3 (Collector / Tab)	Output current terminal and thermal interface	Carries full load current; metal tab is electrically connected to collector and serves as primary heatsink interface.

Key Features

Feature	Design Value
Monolithic Darlington + integrated C–E diode	Eliminates need for external flyback diode in inductive load switching, reducing BOM count and PCB area.
Planar base island technology	Ensures consistent h_FE linearity and thermal stability across production lots and operating temperatures.
Internal base bias resistors (R1 ≈ 15 kΩ, R2 ≈ 100 Ω)	Enables direct connection to 5 V logic outputs without external components, simplifying gate drive circuitry.
ECOPACK® lead-free packaging	Complies with RoHS and JEDEC JESD97 standards; supports environmentally compliant industrial manufacturing.

Applications

Industrial Motor Control

Linear Power Supply Regulator

Use Scenario: Driving 24–48 V DC brushed motors in PLC-controlled conveyor systems with PWM switching at ≤20 kHz.

IC Role / Device Role: Main NPN output switch in H-bridge half-bridge stage, handling bidirectional current up to 3.5 A continuous.

Use Value: Integrated clamping diode prevents voltage spikes during PWM turn-off, eliminating snubber design and improving reliability.

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

IC Role / Device Role: Series pass element operating in linear mode with forced-air heatsinking.

Use Value: High h_FE (>750) reduces base drive current demand, minimizing op-amp output loading and thermal drift.

Switching Power Supply Output Stage

Industrial Relay Driver

Use Scenario: Secondary-side synchronous rectifier driver in 12 V/5 A offline SMPS with 100 kHz switching frequency.

IC Role / Device Role: High-side NPN switch controlling MOSFET gate or driving transformer-coupled gate signal.

Use Value: Fast switching characteristics and low V_CE(sat) reduce drive losses and improve efficiency in auxiliary power rails.

Use Scenario: Solid-state replacement for electromechanical relays controlling 24 V solenoid valves in factory automation panels.

IC Role / Device Role: Single-transistor load switch interfaced directly to 5 V microcontroller GPIO.

Use Value: Internal bias resistors allow direct 5 V logic drive-no external base resistor needed-reducing component count and layout complexity.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD677	Lower V_CEO (60 V), lower h_FE (750 typ. @ 1.5 A), higher V_CE(sat) (2.5 V @ 1.5 A/30 mA)	Suitable only for ≤48 V systems with reduced current gain requirements	Select BD677 where cost sensitivity outweighs voltage margin and thermal performance needs.
MJD127	Higher V_CEO (100 V), no integrated diode, TO-252 (DPAK) package, requires external base resistor	Requires additional flyback diode and base resistor; better for high-voltage, surface-mount designs	Choose MJD127 when board space is constrained and 100 V rating is mandatory, accepting added component count.

Compared with BD677 and MJD127, the BD677A delivers optimal balance of 80 V rating, integrated protection, through-hole manufacturability, and logic-compatible drive-making it preferred for mid-voltage industrial controls where reliability and simplicity are prioritized over ultra-high voltage or SMT density.

Availability

BD677A is available at Aetrix Electronics and suitable for industrial motor control, linear power supply regulation, and switching power supply output stages requiring stable component supply and long-term industrial lifecycle support.

Supply support for BD677A 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The BD6xxx series belongs to ST's complementary power Darlington transistor family, engineered specifically for rugged industrial switching and linear power applications demanding high gain, integrated protection, and thermal resilience.

FAQ

What is the maximum safe operating temperature for BD677A?

The BD677A has a maximum operating junction temperature of 150 °C and a storage temperature range of –65 to +150 °C. Derating is required above 25 °C case temperature per the 40 W P_TOT rating, with thermal resistance R_thJC typically 0.625 °C/W. Heatsink selection must ensure T_J remains below 150 °C under worst-case load and ambient conditions.

Does BD677A require an external flyback diode when driving inductive loads?

No. The BD677A integrates a monolithic antiparallel collector–emitter diode, which provides inherent clamping during inductive turn-off transients. This eliminates the need for an external flyback diode in most relay, solenoid, and DC motor drive applications-reducing component count and PCB footprint.

Can BD677A be driven directly from a 3.3 V microcontroller GPIO?

Not reliably. While the internal R1/R2 network allows 5 V logic compatibility, 3.3 V drive yields insufficient base current to saturate the Darlington at rated current. For 3.3 V systems, a level-shifting buffer or small pre-driver transistor is recommended to ensure I_B ≥ 40 mA at full load.

How does BD677A differ from BD677 in practical circuit design?

The BD677A offers higher V_CEO (80 V vs. 60 V), higher rated I_C (4 A vs. 4 A same, but tested at 2 A vs. 1.5 A), higher h_FE (750 min at 2 A vs. 750 min at 1.5 A), and higher V_CE(sat) (2.8 V vs. 2.5 V). These differences make BD677A more suitable for 48–72 V industrial rails and higher-current linear stages where voltage margin and gain consistency are critical.

BD677A 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):: 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

BD677A FAQ

1.How can I place an order for BD677A through Aetrix?

Please submit a Request for Quotation (RFQ) for BD677A 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 BD677A reliable?

The price and inventory of BD677A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD677A is usually 5 days.

3.What payment methods are accepted for BD677A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD677A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD677A?

BD677A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD677A 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 BD677A?

For technical support, including BD677A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD677A requirements.

6.How does Aetrix verify that BD677A is sourced from the original manufacturer or authorized distributors?

All BD677A 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 BD677A meets industry standards.

7.What is the process for return or replacement of BD677A?

All BD677A units undergo pre-shipment inspection (PSI). If there is an issue with BD677A, 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 BD677A part is unused and in its original packaging.

Return procedure for BD677A:

1.Submit a request within 90 days.

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

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