BD681STU Equivalent & Substitute Parts

Part Overview

The BD681STU 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, necessitating identification of equivalent and substitute components for ongoing design support and procurement continuity. Equivalent parts maintain identical electrical specifications, while substitute parts provide functional alternatives with modified parameters suitable for specific application requirements.

Substiute Parts

BD681STU

onsemiIn Stock: 3976BD681STU Datasheet

Current PartRFQ

BD681G

onsemiIn Stock: 20339BD681G Datasheet

DirectRFQ

BD681

STMicroelectronicsIn Stock: 10498BD681 Datasheet

DirectRFQ

BD677

STMicroelectronicsIn Stock: 1863BD677 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BD681STU is determined by electrical parameter compatibility across the NPN Darlington transistor category. The critical parameters governing substitution are:

Electrical Compatibility Criteria:

• Transistor Type: NPN - Darlington configuration
• Current - Collector (Ic) (Max): 4 A minimum
• Voltage - Collector Emitter Breakdown (Max): 100 V minimum
• DC Current Gain (hFE) (Min): 750 @ 1.5A, 3V minimum
• Power - Max: 40 W minimum
• Vce Saturation characteristics: 2.5V @ 30mA, 1.5A
• Current - Collector Cutoff (Max): 500µA maximum

Mechanical Compatibility Criteria:

• Mounting Type: Through Hole
• Package / Case: TO-225AA or TO-126-3 compatible footprints

Compliance Criteria:

• RoHS3 Compliance required
• REACH Unaffected status

Substitute parts are classified into two categories: direct equivalents maintaining all electrical specifications, and similar parts with reduced voltage ratings suitable for lower-voltage applications.

Parameter Comparison

Engineering Selection Recommendations

Direct Equivalents (100 V Rating):

The BD681G (onsemi) and BD681 (STMicroelectronics) are direct electrical equivalents to the BD681STU, maintaining identical collector current, breakdown voltage, saturation characteristics, and current gain specifications. Both parts are active products with ROHS3 compliance and REACH unaffected status. The BD681G offers extended operating temperature range (-55°C to 150°C) compared to the BD681STU (150°C maximum). Selection between these equivalents depends on packaging preference: BD681G is supplied in bulk packaging with TO-126 supplier device package, while the STMicroelectronics BD681 is supplied in tube packaging with SOT-32-3 supplier device package. Both maintain TO-225AA and TO-126-3 case compatibility.

Voltage-Reduced Substitute (60 V Rating):

The BD677 (STMicroelectronics) is a similar substitute suitable for applications where the collector-emitter breakdown voltage requirement is 60 V or lower. This part maintains identical collector current (4 A), saturation characteristics, current gain, and power dissipation specifications. The BD677 is an active product with ROHS3 compliance. Use of the BD677 is restricted to circuits designed for maximum 60 V operation; it is not suitable for applications requiring 100 V breakdown voltage capability.

Frequently Asked Questions (FAQ)

Q: Can BD681G directly replace BD681STU in existing designs?

A: Yes. The BD681G maintains identical electrical specifications for collector current (4 A), breakdown voltage (100 V), saturation characteristics, and current gain. Both are NPN Darlington transistors in compatible through-hole packages. The BD681G offers extended operating temperature range and is an active product, making it suitable for direct substitution.

Q: What is the difference between BD681 (STMicroelectronics) and BD681G (onsemi)?

A: Both parts are direct electrical equivalents with identical collector current, breakdown voltage, saturation characteristics, and current gain. The primary differences are manufacturer (STMicroelectronics versus onsemi), packaging format (tube versus bulk), and supplier device package designation (SOT-32-3 versus TO-126). Electrical performance is equivalent.

Q: When should BD677 be used instead of BD681STU?

A: The BD677 is suitable only for applications where the maximum required collector-emitter breakdown voltage is 60 V or lower. The BD677 maintains the same 4 A collector current and 40 W power rating. If the circuit design requires 100 V breakdown voltage capability, the BD677 is not appropriate; use BD681G or BD681 instead.

Q: Are there package compatibility concerns between TO-126-3 and SOT-32-3?

A: Both BD681G and BD681 (STMicroelectronics) are specified with TO-225AA and TO-126-3 case compatibility. The supplier device package designation (TO-126 for BD681G, SOT-32-3 for BD681) indicates the physical packaging format from the manufacturer. Verify PCB footprint compatibility with the specific supplier device package before component selection.

Q: Do all substitute parts meet RoHS3 compliance?

A: Yes. BD681G, BD681 (STMicroelectronics), and BD677 are all ROHS3 compliant and REACH unaffected, matching the compliance status of the BD681STU.

Q: What is the operating temperature range difference between BD681STU and BD681G?

A: The BD681STU is rated to 150°C maximum junction temperature. The BD681G extends this to -55°C to 150°C operating range, providing wider temperature capability. Both maintain identical electrical specifications within their respective operating ranges.