RUSB135 Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUSB135 is a polymeric PTC (Positive Temperature Coefficient) resettable fuse manufactured by Littelfuse Inc. in the PolySwitch® series. This component functions as an automatic reset protection device for circuits requiring overcurrent protection at 16V with a 1.35A hold current rating. The RUSB135 is classified as obsolete, making identification of active equivalent parts essential for new designs and ongoing system support. Substitute parts must maintain identical electrical performance characteristics and mechanical compatibility to ensure proper circuit protection without redesign.

Substiute Parts

RUSB135

Littelfuse Inc.In Stock: 919RUSB135 Datasheet

Current PartRFQ

RUSBF135

LittelfuseIn Stock: 941RUSBF135 Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the RUSB135 is determined by strict equivalence across the following critical parameters:

Electrical Parameters: Maximum voltage rating (16V), hold current (1.35A), trip current (2.7A), maximum current (40A), and time to trip (4.5s) must be identical or superior without exceeding circuit design limits.

Mechanical Parameters: Mounting type (Through Hole), package configuration (Radial, Disc), physical dimensions (0.350" L x 0.118" W), and lead spacing (0.199") must match to ensure PCB compatibility without layout modification.

Resistance Characteristics: Initial resistance (Ri minimum 40 mOhms) and post-trip resistance (R1 maximum 115 mOhms) define the protection device's operational behavior and must remain within specified tolerances.

The RUSBF135 qualifies as a direct substitute based on matching all electrical and mechanical parameters while offering improved product status and regulatory compliance.

Parameter Comparison

Engineering Selection Recommendations

The RUSBF135 is the direct substitute for the obsolete RUSB135. Both components share identical electrical specifications and mechanical form factors, ensuring drop-in compatibility without circuit redesign.

The RUSBF135 offers significant advantages for new applications and system updates: Active product status ensures long-term availability and supply chain continuity. ROHS3 compliance satisfies modern environmental and regulatory requirements, whereas the RUSB135 is RoHS non-compliant. Expanded approval certifications (CSA, TUV, UL versus UL only) provide broader market acceptance and regulatory coverage. The post-trip resistance of the RUSBF135 (112 mOhms maximum) is marginally superior to the RUSB135 specification (115 mOhms maximum), representing improved performance consistency.

For applications where the RUSB135 is currently deployed, transition to RUSBF135 is recommended to eliminate obsolescence risk and align with current regulatory standards.

Frequently Asked Questions (FAQ)

Q: Can RUSBF135 be used as a direct replacement for RUSB135 in existing designs?

A: Yes. The RUSBF135 maintains identical electrical parameters (16V, 1.35A hold current, 2.7A trip current, 4.5s trip time) and mechanical specifications (Through Hole, Radial Disc package, 0.350" x 0.118" dimensions, 0.199" lead spacing). No circuit modifications or PCB layout changes are required.

Q: What is the significance of the product status difference between RUSB135 and RUSBF135?

A: RUSB135 is classified as obsolete, indicating discontinued manufacturing and limited availability. RUSBF135 is active, ensuring ongoing production, reliable supply, and manufacturer support. For new designs and long-term system maintenance, active parts are preferred.

Q: How do the resistance specifications compare between these parts?

A: Both components specify 40 mOhms minimum initial resistance (Ri). Post-trip resistance (R1) differs slightly: RUSB135 maximum is 115 mOhms, while RUSBF135 maximum is 112 mOhms. This marginal difference does not affect circuit compatibility and represents equivalent performance.

Q: Are there regulatory or compliance differences between RUSB135 and RUSBF135?

A: Yes. RUSB135 is RoHS non-compliant with UL approval only. RUSBF135 is ROHS3 compliant with CSA, TUV, and UL approvals. For applications subject to environmental regulations or requiring expanded certification coverage, RUSBF135 is the appropriate selection.

Q: What packaging formats are available for RUSBF135?

A: RUSBF135 is supplied in Bag packaging. Both RUSB135 and RUSBF135 use identical Radial Disc package configuration suitable for Through Hole PCB assembly.

Q: Are there operating temperature specifications for these components?

A: RUSB135 does not specify operating temperature limits. RUSBF135 operates across -40°C to 85°C, providing defined thermal performance boundaries for circuit design and environmental compliance.