BD681S NPN Darlington Transistor Equivalent & Substitute Parts

Part Overview

The BD681S is an NPN Darlington bipolar junction transistor manufactured by onsemi, rated for 100 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-126-3 through-hole package. This device is classified as obsolete product status. Locating equivalent and substitute parts is necessary due to obsolescence, ensuring design continuity and procurement availability for applications requiring NPN Darlington transistor functionality with identical or compatible electrical and mechanical specifications.

Substiute Parts

BD681S

onsemiIn Stock: 2237BD681S Datasheet

Current PartRFQ

BD681G

onsemiIn Stock: 20339BD681G Datasheet

DirectRFQ

BD681

STMicroelectronicsIn Stock: 10498BD681 Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BD681S is determined by equivalence across the following critical parameters:

• Transistor Type: NPN - Darlington configuration
• Current Rating: 4 A maximum collector current
• Voltage Rating: 100 V collector-emitter breakdown voltage
• Saturation Characteristics: Vce saturation at specified base and collector currents
• Current Gain: DC current gain (hFE) minimum specification
• Power Dissipation: 40 W maximum power rating
• Mounting: Through-hole technology
• Regulatory Compliance: ROHS3 and REACH status

Substitute parts must maintain identical electrical performance across all specified parameters. Package variations (TO-126-3 versus SOT-32-3) are acceptable provided the through-hole mounting type and pin configuration remain compatible with the application circuit.

Parameter Comparison

Engineering Selection Recommendations

BD681G (onsemi) is the primary substitute for BD681S. Both parts are manufactured by onsemi with identical electrical specifications. BD681G carries active product status, ensuring long-term availability and supply chain continuity. The part is ROHS3 compliant and REACH unaffected. Packaging is supplied in bulk format with TO-126 configuration, compatible with through-hole assembly processes. Operating temperature range extends to -55°C, providing broader environmental capability than the original BD681S specification.

BD681 (STMicroelectronics) is an alternative substitute manufactured by STMicroelectronics with identical electrical performance. This part maintains active product status and full regulatory compliance (ROHS3, REACH unaffected). The device is supplied in tube packaging with SOT-32-3 package designation. Operating temperature specification matches the original BD681S at 150°C maximum junction temperature. Package footprint differs from the original TO-126-3, requiring verification of mechanical compatibility with existing printed circuit board layouts and socket configurations.

Both substitute parts satisfy all electrical parameter requirements and regulatory compliance standards. Selection between BD681G and BD681 depends on packaging availability, supply chain preferences, and mechanical compatibility with the target application circuit board.

Frequently Asked Questions (FAQ)

Q: Can BD681G directly replace BD681S in existing designs?

A: Yes. BD681G maintains identical electrical specifications across all critical parameters: 4 A collector current, 100 V breakdown voltage, 40 W power rating, and DC current gain of 750 minimum. Both parts are NPN Darlington transistors in through-hole packages. Mechanical compatibility requires verification of pin spacing and package outline alignment with existing circuit board layouts.

Q: What is the difference between TO-126-3 and TO-126 packaging?

A: TO-126-3 and TO-126 are variant designations of the same through-hole package family. Both accommodate three-pin Darlington transistor configurations. Mechanical compatibility is maintained across these designations for standard through-hole assembly applications.

Q: Is the STMicroelectronics BD681 compatible with the onsemi BD681S?

A: Yes, from an electrical standpoint. The STMicroelectronics BD681 provides identical electrical performance: 4 A maximum collector current, 100 V breakdown voltage, 40 W power dissipation, and matching saturation characteristics. The device uses SOT-32-3 package designation instead of TO-126-3. Mechanical compatibility with existing circuit board designs requires confirmation of pin configuration and package outline alignment.

Q: Why does BD681G have a wider operating temperature range than BD681S?

A: BD681G specifies -55°C to 150°C operating temperature range, while BD681S specifies 150°C maximum. This difference reflects manufacturer datasheet specifications and does not indicate superior performance. Both parts are electrically equivalent at the specified maximum junction temperature of 150°C. The extended lower temperature specification of BD681G provides additional operational margin in cold environment applications.

Q: Are all three parts ROHS3 compliant?

A: Yes. BD681S, BD681G, and the STMicroelectronics BD681 are all ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements for electronic component manufacturing and distribution.

Q: What determines whether a part can substitute for BD681S?

A: Substitution is determined by equivalence across transistor type (NPN Darlington), current rating (4 A), voltage rating (100 V), saturation characteristics, DC current gain (750 minimum), power rating (40 W), and through-hole mounting configuration. All three parts meet these criteria. Package designation variations are acceptable provided mechanical compatibility with the application circuit is confirmed.