Littelfuse 72R185XF PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The Littelfuse 72R185XF is a polymeric PTC resettable fuse rated for 72V maximum voltage with 1.85A hold current. This component is classified as obsolete, making equivalent substitute parts necessary for new designs and ongoing production support. PTC resettable fuses provide automatic overcurrent protection by increasing resistance when excessive current flows, then resetting when the fault condition clears. Identifying compatible alternatives ensures design continuity and supply chain reliability.

Key Parameters

Parameter	Value
Voltage - Max	72V
Current - Hold (Ih) (Max)	1.85 A
Current - Trip (It)	3.7 A
Current - Max	40 A
Time to Trip	12.6 s
Resistance - Initial (Ri) (Min)	80 mOhms
Resistance - Post Trip (R1) (Max)	190 mOhms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Type	Polymeric

Substitute Part Grouping Explanation

Substitution eligibility for the 72R185XF is determined by strict equivalence across the following critical parameters:

Voltage rating: 72V maximum
Hold current (Ih): 1.85A maximum
Trip current (It): 3.7A
Time to trip: 12.6 seconds
Initial resistance (Ri): 80 mOhms minimum
Post-trip resistance (R1): 190 mOhms maximum
Operating temperature range: -40°C to 85°C
Mounting configuration: Through hole radial disc package
Component type: Polymeric PTC resettable fuse

All identified substitute parts meet these electrical and mechanical specifications. Variations in physical dimensions (diameter, thickness, height, lead spacing) are within acceptable tolerances for through-hole radial mounting applications. Packaging format differences (bag versus bulk) do not affect electrical performance.

Parameter Comparison

Parameter	72R185XF (Littelfuse)	RXEF185K (Littelfuse)	RXEF185K-0.167 (Littelfuse)	RXEF185 (Littelfuse)	MF-RX185/72-0 (Bourns)	PFRY.185 (SCHURTER)
Voltage - Max	72V	72V	72V	72V	72V	72V
Current - Hold (Ih) (Max)	1.85 A	1.85 A	1.85 A	1.85 A	1.85 A	1.85 A
Current - Trip (It)	3.7 A	3.7 A	3.7 A	3.7 A	3.7 A	3.7 A
Current - Max	40 A	40 A	40 A	40 A	40 A	40 A
Time to Trip	12.6 s	12.6 s	12.6 s	12.6 s	12.6 s	12.6 s
Resistance - Initial (Ri) (Min)	80 mOhms	80 mOhms	80 mOhms	80 mOhms	80 mOhms	80 mOhms
Resistance - Post Trip (R1) (Max)	190 mOhms	190 mOhms	190 mOhms	190 mOhms	190 mOhms	190 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole	Through Hole
Package / Case	Radial, Disc	Radial, Disc	Radial, Disc	Radial, Disc	Radial, Disc	Radial, Disc
Type	Polymeric	Polymeric	Polymeric	Polymeric	Polymeric	Polymeric
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Active	Active	Active

Engineering Selection Recommendations

The 72R185XF is obsolete; all substitute parts listed are active products with current manufacturing support. Selection among available substitutes should prioritize product status and regulatory compliance:

RXEF185K and RXEF185K-0.167 are Littelfuse PolySwitch products with active status and expanded approval agencies (CQC, CSA, TUV, UL). These represent direct manufacturer alternatives with the highest compliance coverage.

RXEF185 is the manufacturer-recommended substitute from Littelfuse, designated as the primary active replacement within the PolySwitch RXEF series.

MF-RX185/72-0 is a Bourns Multifuse alternative with active status and cURus/TUV approvals, suitable for applications where multi-source qualification is required.

PFRY.185 is a SCHURTER alternative with active status and cURus/TUV approvals, offering supply chain diversity for critical applications.

All substitutes carry ROHS3 compliance and are rated for identical electrical performance and operating conditions. Physical dimension variations are within acceptable tolerances for through-hole radial mounting.

Frequently Asked Questions (FAQ)

Q: Can RXEF185K directly replace 72R185XF in existing designs? A: Yes. RXEF185K meets all electrical specifications (72V, 1.85A hold current, 3.7A trip current, 12.6s trip time) and physical mounting requirements. The primary difference is product status: 72R185XF is obsolete while RXEF185K is active.

Q: What are the physical dimension differences between substitutes? A: Diameter ranges from 0.598" to 0.689", thickness from 0.118" to 0.122", and height from 0.835" to 0.906". All variations remain compatible with standard through-hole radial mounting footprints. Lead spacing is 0.199" to 0.201", within typical PCB tolerance specifications.

Q: Are all substitutes RoHS compliant? A: Yes. All listed substitutes are ROHS3 compliant, meeting current environmental and hazardous substance restrictions.

Q: Which substitute has the broadest regulatory approvals? A: RXEF185K and RXEF185K-0.167 carry the most comprehensive approval agencies: CQC, CSA, TUV, and UL. This makes them suitable for applications requiring multiple certification standards.

Q: Does packaging format (bag versus bulk) affect electrical performance? A: No. Packaging format is a logistics consideration only. Electrical and mechanical specifications are identical regardless of whether the part is supplied in bag or bulk packaging.

Q: Can I use MF-RX185/72-0 or PFRY.185 if my design was originally qualified to 72R185XF? A: Yes, provided your application requirements are limited to the specified electrical parameters. Both alternatives meet the 72V/1.85A/3.7A trip specifications. Cross-manufacturer qualification may require documentation review depending on your quality or compliance requirements.

Q: What is the difference between RXEF185 and RXEF185K? A: Both are Littelfuse PolySwitch products with identical electrical specifications. RXEF185K includes expanded regulatory approvals (CQC, CSA, TUV, UL) compared to RXEF185. Physical dimensions vary slightly: RXEF185 diameter is 0.689" versus RXEF185K at 0.660".

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