MF-SM125-2-99 Equivalent & Substitute Parts

Part Overview

The MF-SM125-2-99 is a polymeric PTC resettable fuse manufactured by Bourns Inc. in the Multifuse® MF-SM series. This component provides overcurrent protection at 15V with a 1.25A hold current rating in a 2-SMD surface mount package. The part is currently obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. Alternative parts maintain the same electrical performance characteristics while offering active product status and improved availability.

Key Parameters

Parameter	Value
Voltage - Max	15V
Current - Hold (Ih) (Max)	1.25 A
Current - Trip (It)	2.5 A
Resistance - Initial (Ri) (Min)	70 mOhms
Resistance - Post Trip (R1) (Max)	250 mOhms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package / Case	2-SMD
Type	Polymeric
Time to Trip	2 s

Substitute Part Grouping Explanation

Substitute parts are classified into three categories based on electrical and mechanical compatibility with the MF-SM125-2-99:

Parametric Equivalents (Bourns Inc.): MF-SM125-2 and MF-SM125-2-006 are direct parametric equivalents from the same manufacturer. These parts match all critical electrical parameters: 15V maximum voltage, 1.25A hold current, 2.5A trip current, 70 mOhms initial resistance, and 250 mOhms post-trip resistance. Both maintain the 2-SMD surface mount package and -40°C to 85°C operating temperature range. The primary difference is product status and packaging format (MF-SM125-2 is active with Tape & Reel packaging; MF-SM125-2-006 is active with standard packaging).

Direct Manufacturer Equivalents (Alternative Suppliers): PFSM.125.2 (SCHURTER Inc.) and SMD125F-2 (Littelfuse Inc.) provide electrical equivalence with identical voltage, hold current, trip current, and operating temperature specifications. Both use 2-SMD surface mount packages. Dimensional variations are minimal (length differences of 0.002" to 0.003"). PFSM.125.2 matches the 250 mOhms post-trip resistance specification; SMD125F-2 does not specify this parameter but maintains the 70 mOhms initial resistance minimum.

Similar Parts (Different Form Factor): LR4-190F and LR4-260SF are strap-mounted polymeric PTC fuses from Littelfuse Inc. with 15V maximum voltage ratings. These parts differ significantly in hold current (1.9A and 2.6A respectively) and mounting type (user-defined strap versus surface mount). These are listed as similar alternatives only when form factor change is acceptable.

Parameter Comparison

Part Number	Manufacturer	Voltage - Max	Current - Hold (Ih)	Current - Trip (It)	Ri (Min)	R1 (Max)	Operating Temp	Package	Product Status
MF-SM125-2-99	Bourns Inc.	15V	1.25 A	2.5 A	70 mOhms	250 mOhms	-40°C ~ 85°C	2-SMD	Obsolete
MF-SM125-2	Bourns Inc.	15V	1.25 A	2.5 A	70 mOhms	250 mOhms	-40°C ~ 85°C	2-SMD	Active
MF-SM125-2-006	Bourns Inc.	15V	1.25 A	2.5 A	70 mOhms	250 mOhms	-40°C ~ 85°C	2-SMD	Active
PFSM.125.2	SCHURTER Inc.	15V	1.25 A	2.5 A	70 mOhms	250 mOhms	-40°C ~ 85°C	2-SMD	Active
SMD125F-2	Littelfuse Inc.	15V	1.25 A	2.5 A	70 mOhms	Not Specified	-40°C ~ 85°C	2-SMD	Active
LR4-190F	Littelfuse Inc.	15V	1.9 A	3.9 A	39 mOhms	102 mOhms	-40°C ~ 85°C	Strap	Active
LR4-260SF	Littelfuse Inc.	15V	2.6 A	5.8 A	20 mOhms	63 mOhms	-40°C ~ 85°C	Strap	Active

Engineering Selection Recommendations

Primary Substitutes: MF-SM125-2 and MF-SM125-2-006 are the recommended direct replacements. Both are active Bourns products with identical electrical specifications and 2-SMD surface mount packaging. MF-SM125-2 offers higher inventory availability (5400 pcs) with Tape & Reel packaging suitable for automated assembly. MF-SM125-2-006 provides an alternative with 759 pcs in stock. Both maintain ROHS3 compliance, AEC-Q200 ratings, and cURus/TUV approvals matching the original part.

Alternative Manufacturer Equivalents: PFSM.125.2 (SCHURTER Inc.) and SMD125F-2 (Littelfuse Inc.) provide full electrical equivalence with identical hold and trip current specifications. PFSM.125.2 maintains complete parameter matching including post-trip resistance specification. SMD125F-2 offers the highest inventory (7276 pcs) but does not specify post-trip resistance. Both are active products with ROHS3 compliance. Dimensional variations are within 0.003" and do not affect PCB layout compatibility for standard 2-SMD footprints.

Form Factor Alternatives: LR4-190F and LR4-260SF are suitable only when strap mounting is acceptable and higher hold current ratings are compatible with circuit design. These parts are not direct substitutes due to different mounting type and current ratings.

Frequently Asked Questions (FAQ)

Q: Can MF-SM125-2 directly replace MF-SM125-2-99 without circuit modification?

A: Yes. MF-SM125-2 is a parametric equivalent with identical voltage, hold current, trip current, resistance specifications, and operating temperature range. The 2-SMD surface mount package and footprint are identical. No circuit modification is required.

Q: What is the difference between MF-SM125-2 and MF-SM125-2-006?

A: Both are parametric equivalents with identical electrical specifications. The difference is packaging format: MF-SM125-2 is supplied in Tape & Reel format suitable for automated assembly, while MF-SM125-2-006 uses standard packaging. Selection depends on assembly process requirements.

Q: Can PFSM.125.2 or SMD125F-2 be used as direct substitutes?

A: Yes, both are direct manufacturer equivalents with matching 15V voltage, 1.25A hold current, 2.5A trip current, and 70 mOhms initial resistance. PFSM.125.2 also matches the 250 mOhms post-trip resistance specification. Dimensional differences are minimal (0.002" to 0.003" in length) and do not affect standard 2-SMD PCB footprints.

Q: Are LR4-190F and LR4-260SF suitable replacements?

A: LR4-190F and LR4-260SF are not direct substitutes. These strap-mounted parts have different hold current ratings (1.9A and 2.6A respectively) and require user-defined strap mounting instead of surface mount. Use these only when form factor change and higher current ratings are acceptable for the application.

Q: What compliance certifications should I verify for substitute parts?

A: All recommended substitutes (MF-SM125-2, MF-SM125-2-006, PFSM.125.2, and SMD125F-2) maintain ROHS3 compliance and REACH unaffected status. MF-SM125-2, MF-SM125-2-006, and PFSM.125.2 carry AEC-Q200 ratings with cURus and TUV approvals. SMD125F-2 carries ROHS3 compliance with REACH unaffected status. Verify specific certifications required by your application before final selection.

Q: How do I select between multiple equivalent parts?

A: Selection priority: (1) MF-SM125-2 for highest availability and Tape & Reel packaging; (2) PFSM.125.2 for complete parameter specification matching; (3) SMD125F-2 for alternative supplier diversity. All three are electrically equivalent and suitable for direct substitution in the MF-SM125-2-99 application.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message