SMM 25 Surface Mount Fuse Equivalent & Substitute Parts

Part Overview

The SMM 25 is a 25 A, 250 V AC / 72 V DC surface mount board fuse manufactured by Bel Fuse Inc. in a 2-SMD square end block package. This part is classified as obsolete, making identification of equivalent and substitute components essential for ongoing design support and procurement continuity. Substitute parts must maintain electrical compatibility across current rating, voltage specifications, and thermal characteristics while accommodating available active alternatives.

Substiute Parts

SMM 25

Bel Fuse Inc.In Stock: 766SMM 25 Datasheet

Current PartRFQ

0678L9100-02

Bel Fuse Inc.In Stock: 218070678L9100-02 Datasheet

DirectRFQ

0678L9250-02

Bel Fuse Inc.In Stock: 391450678L9250-02 Datasheet

DirectRFQ

0456025.ER

Littelfuse Inc.In Stock: 51150456025.ER Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the SMM 25 are classified into two categories based on electrical parameter alignment:

Direct Substitutes (Identical Electrical Specifications): Parts maintaining 25 A current rating, 250 V AC / 72 V DC voltage ratings, medium blow response, and equivalent breaking capacity qualify as direct substitutes. These parts preserve all critical electrical parameters and thermal characteristics.

Similar Substitutes (Voltage Derating Required): Parts with matching current rating (25 A), DC voltage rating (72 V), and package form factor but reduced AC voltage rating (125 V vs. 250 V) are classified as similar substitutes. These parts require circuit-level voltage verification before implementation, as the reduced AC voltage rating represents a design constraint.

Key parameters determining substitution eligibility:

• Current Rating (Amps): Must equal 25 A
• Voltage Rating - DC: Must equal 72 V
• Mounting Type: Must be Surface Mount
• Package / Case: Must be 2-SMD, Square End Block
• Operating Temperature Range: Must support -55°C ~ 125°C

Parameter Comparison

Engineering Selection Recommendations

0678L9250-02 (Bel Fuse Inc.) is the primary direct substitute for SMM 25. This part maintains identical electrical specifications including 25 A current rating, 250 V AC / 72 V DC voltage ratings, medium blow response, and equivalent melting I²t value of 420. The part is active in production status with ROHS3 compliance and AEC-Q200 automotive qualification, providing enhanced supply chain stability compared to the obsolete SMM 25. Inventory availability of 39,057 units supports immediate procurement.

0456025.ER (Littelfuse Inc. NANO²® 456 series) functions as a similar substitute with design constraints. While maintaining 25 A current rating, 72 V DC voltage rating, and compatible package form factor, the AC voltage rating is reduced to 125 V. This part exhibits fast blow response (versus medium blow) and significantly lower melting I²t of 45 (versus 420), indicating faster thermal response. The part is active in production with cULus and PSE certifications. Implementation requires circuit-level verification that the 125 V AC rating is acceptable for the application and that the fast blow characteristic does not conflict with system protection requirements.

0678L9100-02 (Bel Fuse Inc.) is not recommended as a substitute for SMM 25 due to reduced current rating (10 A versus 25 A), which does not meet the electrical requirements of circuits designed for 25 A protection.

Frequently Asked Questions (FAQ)

Q: Can 0678L9250-02 be used as a direct replacement for SMM 25?

A: Yes. The 0678L9250-02 maintains identical current rating (25 A), AC voltage rating (250 V), DC voltage rating (72 V), response time (medium blow), and melting I²t (420). The part is mechanically and electrically compatible with SMM 25 applications without circuit modification.

Q: What are the limitations of using 0456025.ER as a substitute?

A: The 0456025.ER has a reduced AC voltage rating of 125 V compared to the SMM 25 specification of 250 V. Additionally, the response time is fast blow rather than medium blow, and the melting I²t is significantly lower at 45 versus 420. These differences require verification that the application circuit operates at or below 125 V AC and that the faster thermal response does not create nuisance trip conditions.

Q: Are all substitute parts available in the same packaging format?

A: Yes. Both 0678L9250-02 and 0456025.ER are supplied in Tape & Reel (TR) packaging and feature 2-SMD square end block packages compatible with SMM 25 board layouts. Tape & Reel packaging is standard for surface mount production assembly.

Q: What certifications should I verify for substitute parts?

A: The 0678L9250-02 carries AEC-Q200 and cURus approvals with ROHS3 compliance. The 0456025.ER carries cULus and PSE approvals with ROHS3 compliance. Verify that substitute part certifications meet your application's regulatory and quality requirements.

Q: Why is SMM 25 classified as obsolete?

A: The SMM 25 is no longer in active production. The 0678L9250-02 from the active 0678L series provides equivalent electrical performance with current manufacturing support and improved supply chain availability.