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

STMicroelectronics BD681

Name: BD681
Brand: STMicroelectronics
SKU: BD681
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD681

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BD681.pdf

Description:: TRANS NPN DARL 100V 4A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:1,501

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Product details

Overview

BD681 from STMicroelectronics is an NPN complementary power Darlington transistor in SOT-32 package, featuring 100 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 circuits.

For engineers reviewing the BD681 datasheet, BD681 pinout, BD681 application, or BD681 equivalent, key selection criteria include V_CEO(sus) = 100 V, V_CE(sat) = 2.5 V @ 1.5 A/30 mA, thermal derating above T_case = 25°C, monolithic Darlington architecture with built-in clamping diode, and planar base island process for stable h_FE linearity.

Technical Context

The BD681 employs a monolithic Darlington configuration with two cascaded NPN stages on a single die, enabling high current gain without external bias networks. Its integrated antiparallel collector-emitter diode provides inherent reverse-voltage protection during inductive load switching.

Designed using planar base island technology (replacing earlier epybase), it delivers improved f_T frequency response and consistent h_FE linearity across operating current range-critical for analog linear regulation and precision PWM motor drive stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	100 V sustained collector-emitter voltage at I_C = 50 mA - enables safe operation with 80–100 V DC bus rails
I_C	4 A continuous collector current - supports medium-power industrial loads without forced cooling
h_FE	≥750 @ I_C = 1.5 A, V_CE = 3 V - reduces required base drive current to ≤2 mA for full conduction
V_CE(sat)	2.5 V @ I_C = 1.5 A, I_B = 30 mA - limits conduction loss to ≤3.75 W at rated current
P_TOT	40 W @ T_case = 25°C - requires heatsink for >10 W dissipation in ambient >40°C
f_T	High frequency transition - supports switching up to ~100 kHz in non-resonant topologies

Pinout & Package

SOT-32 (TO-126) three-terminal plastic package with emitter-base-collector pin sequence (1–2–3), thermally optimized for PCB-mount heatsinking via tab-connected collector terminal.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current return path	Low-impedance connection to ground/reference rail; internally bonded to substrate for thermal stability
2 (Base)	Control input	Drives first transistor stage; requires series resistor to limit I_B ≤ 100 mA peak
3 (Collector)	Main output node	Tab-connected high-current output; electrically and thermally coupled to heatsink mounting surface

Key Features

Feature	Design Value
Monolithic Darlington structure	Single-die integration eliminates inter-stage parasitics and ensures matched thermal tracking between driver and output transistors
Integrated antiparallel C–E diode	Eliminates need for external flyback diode in relay/inductor drive, reducing BOM count and layout area
Planar base island technology	Enables tighter h_FE distribution (±15%) and higher f_T vs. older epybase process
ECOPACK® lead-free packaging	Meets RoHS Directive 2011/65/EU and JEDEC JESD97 marking requirements for second-level interconnect

Applications

Industrial Linear Regulators

DC Motor Drive Stages

Use Scenario: High-stability 0–30 V, 3 A adjustable bench power supply with analog feedback loop.

IC Role / Device Role / Timing Role: Pass transistor regulating output voltage under op-amp error amplifier control.

Use Value: High h_FE minimizes base drive burden on error amp; low V_CE(sat) reduces dropout and thermal load at full current.

Use Scenario: Unidirectional 24–48 V brushed DC motor controller with PWM input and freewheeling path.

IC Role / Device Role / Timing Role: Main switching element in low-side configuration driving motor winding to ground.

Use Value: Integrated C–E diode provides automatic freewheeling during PWM off-time, eliminating external diode and associated layout complexity.

Relay Driver Circuits

High-Current Switching Power Supplies

Use Scenario: Solid-state replacement for 24 V/1 A electromagnetic relays in PLC output modules.

IC Role / Device Role / Timing Role: Final-stage switch energizing relay coil with controlled turn-on/turn-off timing.

Use Value: 100 V V_CEO(sus) withstands coil back-EMF spikes; fast switching enables <100 µs release time.

Use Scenario: 48 V input, 12 V/5 A output linear post-regulator in telecom power shelf.

IC Role / Device Role / Timing Role: Series pass element dissipating variable power based on load and input ripple.

Use Value: 40 W P_TOT allows operation up to 3 A at 12 V dropout without active cooling in 50°C ambient.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD679	V_CEO(sus) = 80 V, h_FE ≥ 750 @ I_C = 1.5 A, same SOT-32 package	Limited to ≤60 V bus systems; lower voltage margin for inductive kick suppression	Select when 80 V rating suffices and cost optimization is prioritized over headroom
TIP122	V_CEO = 100 V, I_C = 5 A, but no integrated C–E diode; TO-220 package	Requires external flyback diode; larger footprint and higher thermal resistance than SOT-32	Choose only if TO-220 mechanical fit is mandatory and board space permits added component

Compared with BD679, BD681 offers 20 V higher sustaining voltage for robustness in noisy industrial environments; versus TIP122, it integrates clamping functionality and uses a smaller, thermally efficient SOT-32 package-reducing total solution size and assembly steps.

Availability

BD681 is available at Aetrix Electronics and suitable for industrial linear regulators, DC motor drive stages, relay driver circuits, and high-current switching power supplies requiring stable component supply and long-term obsolescence management.

Supply support for BD681 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, Switzerland, designing and manufacturing microcontrollers, power transistors, sensors, and analog ICs for industrial, automotive, and consumer markets.

The BD6xxx series targets high-reliability industrial power control, delivering rugged Darlington transistors optimized for linear regulation, switching, and inductive load handling with integrated protection features.

FAQ

What is the maximum safe operating junction temperature for BD681?

The BD681 has a maximum operating junction temperature of 150°C. Derating begins at T_case > 25°C per the thermal resistance curve in Section 3 of the datasheet. At T_case = 75°C, maximum allowable P_TOT drops to ~20 W. Thermal design must ensure case-to-heatsink interface resistance remains ≤1.5°C/W for reliable operation at full current.

Does BD681 require an external base resistor, and what value is recommended?

Yes, BD681 requires an external base resistor to limit I_B within its 0.1 A absolute maximum rating. For I_C = 1.5 A and h_FE ≥ 750, I_B ≈ 2 mA is sufficient. With a 5 V logic drive, R_B = (5 V − V_BE) / 2 mA ≈ 2.2 kΩ (V_BE ≈ 2.5 V). Use 1.8–2.7 kΩ for margin against parameter spread and temperature drift.

Can BD681 be used in parallel configurations for higher current handling?

Parallel operation is not recommended due to mismatch in h_FE and V_CE(sat) between units, leading to current imbalance and thermal runaway. The datasheet does not specify matching tolerances or recommend emitter ballasting. For >4 A applications, select a higher-rated device such as BD682 (same family, 100 V/6 A) or consider MOSFET alternatives with positive temperature coefficient behavior.

Is BD681 compliant with modern environmental regulations like RoHS and REACH?

Yes, BD681 is supplied in ECOPACK® packaging, which meets RoHS Directive 2011/65/EU and REACH SVHC requirements. The lead-free second-level interconnect is marked on both the package and inner box label per JEDEC JESD97. STMicroelectronics confirms full compliance documentation is available upon request for audit or certification purposes.

BD681 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):: 100 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

BD681 FAQ

1.How can I place an order for BD681 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD681 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 BD681 reliable?

The price and inventory of BD681 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD681 is usually 5 days.

3.What payment methods are accepted for BD681?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD681 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD681?

BD681 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD681 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 BD681?

For technical support, including BD681 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD681 requirements.

6.How does Aetrix verify that BD681 is sourced from the original manufacturer or authorized distributors?

All BD681 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 BD681 meets industry standards.

7.What is the process for return or replacement of BD681?

All BD681 units undergo pre-shipment inspection (PSI). If there is an issue with BD681, 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 BD681 part is unused and in its original packaging.

Return procedure for BD681:

1.Submit a request within 90 days.

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

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