BD681 Equivalent & Substitute Parts

Part Overview

The BD681 is an NPN Darlington bipolar junction transistor manufactured by onsemi, designed for through-hole applications in the TO-126 package. This device is rated for 100 V collector-emitter breakdown voltage, 4 A maximum collector current, and 40 W maximum power dissipation, with an operating temperature range of -55°C to 150°C. The BD681 is classified as obsolete, necessitating identification of equivalent and substitute components for ongoing design support and procurement continuity.

Substiute Parts

BD681

onsemiIn Stock: 10490BD681 Datasheet

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BD681G

onsemiIn Stock: 20339BD681G Datasheet

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BD681

STMicroelectronicsIn Stock: 10498BD681 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the BD681 is determined by electrical and mechanical parameter equivalence across the following criteria:

Electrical Parameters (Critical for Functional Equivalence):

• Transistor type: NPN - Darlington configuration
• Maximum collector current: 4 A
• Maximum collector-emitter breakdown voltage: 100 V
• Saturation voltage characteristics: 2.5V @ 30mA, 1.5A
• Collector cutoff current: 500µA
• DC current gain (hFE): 750 @ 1.5A, 3V
• Maximum power dissipation: 40 W
• Operating temperature range: -55°C to 150°C

Mechanical Parameters (Required for Physical Compatibility):

• Mounting type: Through Hole
• Package designation: TO-126-3 or equivalent TO-225AA

Substitute parts are grouped into two categories: direct equivalents (identical electrical and mechanical specifications with different product status or compliance ratings) and alternative manufacturers offering the same electrical performance in compatible packages.

Parameter Comparison

Engineering Selection Recommendations

BD681G (onsemi) is the primary direct substitute for the obsolete BD681. This part maintains identical electrical specifications and through-hole mounting compatibility while offering active product status and ROHS3 compliance. The BD681G is suitable for new designs and replacement applications where RoHS compliance is required.

BD681 (STMicroelectronics) provides an alternative source from a different manufacturer with equivalent electrical performance. This part is active and ROHS3 compliant. The package designation differs (SOT-32-3 versus TO-126), requiring verification of physical fit within existing PCB layouts and mechanical assemblies. The operating temperature specification lists only the maximum junction temperature (150°C) without the minimum temperature specification, differing from the onsemi variants.

For applications requiring the original TO-126 package form factor without modification, BD681G is the recommended substitute. For applications where alternative packaging is acceptable, the STMicroelectronics BD681 provides additional sourcing flexibility.

Frequently Asked Questions (FAQ)

Q: Can BD681G be used as a direct replacement for the obsolete BD681?

A: Yes. BD681G maintains identical electrical parameters (4 A collector current, 100 V breakdown voltage, 40 W power rating, 750 hFE minimum gain) and through-hole TO-126 package compatibility. The primary differences are product status (active versus obsolete) and RoHS compliance (ROHS3 compliant versus non-compliant).

Q: What is the difference between BD681 and BD681G from onsemi?

A: Both parts are electrically identical NPN Darlington transistors with the same electrical ratings and TO-126 package. BD681 is obsolete with RoHS non-compliant status, while BD681G is active with ROHS3 compliance. BD681G is the recommended choice for new procurement.

Q: Is the STMicroelectronics BD681 compatible with existing PCB designs for the onsemi BD681?

A: Electrical compatibility is confirmed through identical electrical specifications. Physical compatibility depends on the package designation: the STMicroelectronics part uses SOT-32-3 packaging while the onsemi parts use TO-126. PCB layout verification is required to confirm mechanical fit, as pin spacing and lead geometry may differ between package types.

Q: What are the critical electrical parameters that define substitution for the BD681?

A: Substitution is determined by matching the following parameters: NPN Darlington transistor type, 4 A maximum collector current, 100 V collector-emitter breakdown voltage, 2.5V saturation voltage at specified bias conditions, 500µA collector cutoff current, 750 minimum hFE at 1.5A and 3V, and 40 W maximum power dissipation.

Q: Are there compliance or certification differences between the substitute parts?

A: Yes. The original BD681 is RoHS non-compliant. BD681G and the STMicroelectronics BD681 are both ROHS3 compliant. All three parts are REACH unaffected and classified under ECCN EAR99. For applications requiring RoHS compliance, BD681G or the STMicroelectronics alternative must be selected.

Q: What is the operating temperature range for each substitute?

A: The onsemi BD681 and BD681G both specify -55°C to 150°C junction temperature. The STMicroelectronics BD681 specifies 150°C maximum junction temperature without a minimum specification provided in the available data.