RUSB250 PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUSB250 is a polymeric PTC resettable fuse manufactured by Littelfuse Inc. under the PolySwitch® series. This component is rated for 16V maximum voltage with a 2.5A hold current and is designed for through-hole radial mounting in disc configuration. The RUSB250 is currently listed as obsolete, making identification of active equivalent parts essential for ongoing design support and procurement.

Key Parameters

Parameter	Value
Voltage - Max	16V
Current - Hold (Ih) (Max)	2.5 A
Current - Trip (It)	5 A
Current - Max	40 A
Time to Trip	40 s
Resistance - Initial (Ri) (Min)	20 mOhms
Resistance - Post Trip (R1) (Max)	60 mOhms
Mounting Type	Through Hole
Package / Case	Radial, Disc
Size / Dimension	0.449" L x 0.118" W (11.40mm x 3.00mm)
Height - Seated (Max)	0.720" (18.30mm)
Lead Spacing	0.199" (5.05mm)
Type	Polymeric
Series	PolySwitch®

Substitute Part Grouping Explanation

Substitution of the RUSB250 is determined by strict equivalence across the following critical parameters:

Voltage rating: 16V maximum
Current hold specification: 2.5A
Current trip specification: 5A
Mounting configuration: Through hole radial disc
Physical dimensions: 11.40mm x 3.00mm length and width
Electrical characteristics: 20 mOhms initial resistance minimum, 60 mOhms post-trip maximum

The RUSBF250 qualifies as a direct substitute based on identical electrical ratings and mechanical form factor. Both components share the same voltage, hold current, trip current, and physical dimensions required for PCB compatibility.

Parameter Comparison

Parameter	RUSB250	RUSBF250
Manufacturer	Littelfuse Inc.	Littelfuse Inc.
Series	PolySwitch®	PolySwitch®, RUSBF
Product Status	Obsolete	Active
Type	Polymeric	Polymeric
Voltage - Max	16V	16V
Current - Hold (Ih) (Max)	2.5 A	2.5 A
Current - Trip (It)	5 A	5 A
Current - Max	40 A	40 A
Time to Trip	40 s	40 s
Resistance - Initial (Ri) (Min)	20 mOhms	20 mOhms
Resistance - Post Trip (R1) (Max)	60 mOhms	60 mOhms
Mounting Type	Through Hole	Through Hole
Package / Case	Radial, Disc	Radial, Disc
Size / Dimension	0.449" L x 0.118" W (11.40mm x 3.00mm)	0.449" L x 0.118" W (11.40mm x 3.00mm)
Height - Seated (Max)	0.720" (18.30mm)	0.720" (18.30mm)
Lead Spacing	0.199" (5.05mm)	0.118" (3.00mm)
Operating Temperature	Not specified	-40°C ~ 85°C
RoHS Status	RoHS non-compliant	ROHS3 Compliant
Approval Agency	CSA, TUV, UR	CSA, TUV, UL

Engineering Selection Recommendations

The RUSBF250 is the active equivalent for the obsolete RUSB250. Both components are manufactured by Littelfuse Inc. and share identical electrical specifications and mechanical form factors. The RUSBF250 offers the advantage of active product status, ensuring continued availability and supply chain support.

The RUSBF250 provides improved compliance posture with ROHS3 certification compared to the non-compliant RUSB250. Operating temperature range is specified for the RUSBF250 (-40°C ~ 85°C), providing defined thermal performance boundaries. Approval certifications differ slightly, with the RUSBF250 carrying UL certification in place of UR certification on the original part.

Lead spacing differs between the two parts (0.199" versus 0.118"), which may require PCB layout verification during substitution to ensure hole-to-hole spacing compatibility with existing designs.

Frequently Asked Questions (FAQ)

Q: Can RUSBF250 be used as a direct replacement for RUSB250?

A: Yes. Both components share identical voltage ratings (16V), hold current (2.5A), trip current (5A), and physical dimensions (11.40mm x 3.00mm). Electrical performance characteristics including initial resistance and post-trip resistance are equivalent.

Q: What is the difference in lead spacing between RUSB250 and RUSBF250?

A: RUSB250 has 0.199" (5.05mm) lead spacing, while RUSBF250 has 0.118" (3.00mm) lead spacing. PCB hole patterns must be verified for compatibility before substitution.

Q: Does RUSBF250 meet RoHS requirements?

A: Yes. RUSBF250 is ROHS3 compliant. The original RUSB250 is RoHS non-compliant. If RoHS compliance is required for your application, RUSBF250 satisfies this requirement.

Q: Are the approval certifications equivalent?

A: Both parts carry CSA and TUV certifications. RUSB250 includes UR certification, while RUSBF250 includes UL certification. Both certifications are recognized standards for electrical safety.

Q: What is the operating temperature range for these components?

A: RUSBF250 is specified for -40°C to 85°C operation. Operating temperature is not specified for the obsolete RUSB250.

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