78F681J Equivalent & Substitute Parts

Part Overview

The Bourns 78F681J is a 680 µH unshielded drum core wirewound inductor rated for 45 mA maximum current with 18Ω DC resistance. This through-hole axial component operates across -55°C to 105°C and is designed for applications requiring fixed inductance filtering and energy storage. The 78F681J is currently obsolete, necessitating identification of functionally equivalent active alternatives to maintain design continuity and ensure supply chain availability.

Substiute Parts

78F681J

Bourns Inc.In Stock: 79578F681J Datasheet

Current PartRFQ

78F681J-RC

Bourns Inc.In Stock: 517678F681J-RC Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

The 78F681J-RC qualifies as a direct substitute based on the following matching parameters:

• Inductance Value: Both parts are 680 µH with ±5% tolerance
• Core Type: Ferrite drum core construction in both parts
• Shielding: Unshielded configuration maintained
• Mounting: Through-hole axial package identical
• Physical Dimensions: 0.110" Dia × 0.280" L (2.79mm × 7.11mm)
• Operating Temperature Range: -55°C to 105°C
• Frequency Characteristics: Q @ 790 kHz and 2 MHz self-resonant frequency match

The 78F681J-RC exhibits higher current rating (68 mA vs. 45 mA) and increased DC resistance (25.3Ω vs. 18Ω), representing a design variant within the same product family. These parameter differences do not preclude substitution in applications where the original 45 mA rating provides design margin.

Parameter Comparison

Engineering Selection Recommendations

The 78F681J-RC is the designated substitute for the obsolete 78F681J. Selection is based on:

Product Status: The 78F681J-RC maintains active production status with 5100 units in stock, compared to the obsolete 78F681J with limited remaining inventory (749 units).

Regulatory Compliance: The 78F681J-RC achieves ROHS3 compliance, whereas the original 78F681J is RoHS non-compliant. For applications subject to RoHS directives, the 78F681J-RC is the required selection.

Electrical Compatibility: The 68 mA current rating of the 78F681J-RC exceeds the original 45 mA specification, providing enhanced current handling capability. The increased DC resistance (25.3Ω vs. 18Ω) represents a 7.3Ω differential that must be evaluated in circuits where DCR contributes to total impedance or power dissipation calculations.

Physical and Functional Equivalence: Identical inductance value, tolerance, core material, shielding, mounting type, package dimensions, and operating temperature range ensure direct mechanical and electrical interchangeability in PCB layouts and circuit designs.

Frequently Asked Questions (FAQ)

Q: Can the 78F681J-RC replace the 78F681J in existing designs?

A: Yes. The 78F681J-RC is electrically and mechanically equivalent. Both parts share identical inductance (680 µH), tolerance (±5%), core type (ferrite), shielding (unshielded), mounting (through-hole axial), dimensions, and operating temperature range. The higher current rating (68 mA vs. 45 mA) and increased DCR (25.3Ω vs. 18Ω) must be evaluated for circuit-specific impact.

Q: What is the impact of the increased DC resistance in the 78F681J-RC?

A: The 78F681J-RC exhibits 25.3Ω maximum DCR compared to 18Ω in the 78F681J, a 7.3Ω increase. In DC or low-frequency applications, this increases resistive losses and heat dissipation. Circuit analysis is required to determine if this differential affects performance or thermal management.

Q: Are there packaging differences between these parts?

A: No. Both parts use identical through-hole axial packaging with 0.110" diameter and 0.280" length (2.79mm × 7.11mm). PCB footprints and lead spacing are identical.

Q: Why is RoHS compliance important for this substitution?

A: The 78F681J-RC is ROHS3 compliant while the 78F681J is RoHS non-compliant. Designs destined for markets with RoHS regulations must use the 78F681J-RC. The original part may no longer be procurable for new production due to regulatory restrictions.

Q: Do the frequency characteristics differ between these parts?

A: No. Both parts maintain Q @ 790 kHz of 60 and self-resonant frequency of 2 MHz, ensuring identical high-frequency performance.