SRP350 Equivalent & Substitute Parts

Part Overview

The SRP350 is a polymeric PTC resettable fuse manufactured by Littelfuse Inc. in the PolySwitch® SRP series, rated for 30V maximum voltage and 4.6A hold current. This component is classified as obsolete, making equivalent substitute parts necessary for ongoing design support and procurement. The SRP350 is designed for overcurrent protection applications requiring automatic reset functionality in strap package configuration.

Key Parameters

Parameter	Value
Voltage - Max	30V
Current - Hold (Ih) (Max)	4.6 A
Current - Trip (It)	6.3 A
Current - Max	100 A
Time to Trip	3 s
Resistance - Initial (Ri) (Min)	17 mOhms
Operating Temperature	-40°C ~ 85°C
Type	Polymeric
Package / Case	Strap
Size / Dimension	1.185" L x 0.522" W (30.10mm x 13.25mm)
Thickness (Max)	0.043" (1.10mm)
Approval Agency	CSA, TUV, UL

Substitute Part Grouping Explanation

Substitution for the SRP350 is determined by strict equivalence across the following critical parameters:

Voltage rating: 30V maximum
Hold current (Ih): 4.6A maximum
Trip current (It): 6.3A
Time to trip: 3 seconds
Initial resistance (Ri): 17 mOhms minimum
Operating temperature range: -40°C to 85°C
Package type: Strap configuration
Physical dimensions: 1.185" L x 0.522" W (30.10mm x 13.25mm)
Polymeric PTC resettable fuse technology

Three substitute parts meet these electrical and mechanical specifications across different manufacturers.

Parameter Comparison

Parameter	SRP350	SRP350F	MF-S350	0ZSA0350FF1E
Manufacturer	Littelfuse Inc.	Littelfuse Inc.	Bourns Inc.	Bel Fuse Inc.
Series	PolySwitch® SRP	PolySwitch® SRP	Multifuse® MF-S	0ZSA
Product Status	Obsolete	Active	Active	Active
Voltage - Max	30V	30V	30V	30V
Current - Hold (Ih) (Max)	4.6 A	4.6 A	4.6 A	4.6 A
Current - Trip (It)	6.3 A	6.3 A	6.3 A	6.3 A
Current - Max	100 A	100 A	100 A	100 A
Time to Trip	3 s	3 s	3 s	3 s
Resistance - Initial (Ri) (Min)	17 mOhms	17 mOhms	17 mOhms	17 mOhms
Resistance - Post Trip (R1) (Max)	50 mOhms	50 mOhms	40 mOhms	50 mOhms
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Type	Polymeric	Polymeric	Polymeric	Polymeric
Package / Case	Strap	Strap	Strap	Strap
Size / Dimension	1.185" L x 0.522" W (30.10mm x 13.25mm)	1.185" L x 0.522" W (30.10mm x 13.25mm)	1.185" L x 0.522" W (30.10mm x 13.25mm)	1.185" L x 0.522" W (30.10mm x 13.25mm)
Thickness (Max)	0.043" (1.10mm)	0.043" (1.10mm)	0.043" (1.10mm)	0.043" (1.10mm)
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	2A (4 Weeks)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)
Approval Agency	CSA, TUV, UL	CSA, TUV, UL	cURus, TUV	cURus, TUV

Engineering Selection Recommendations

SRP350F (Littelfuse Inc.) is the primary substitute for the obsolete SRP350. Both parts share identical electrical specifications and are from the same manufacturer series. SRP350F carries active product status and is ROHS3 compliant, addressing regulatory requirements that the original SRP350 does not meet. Moisture sensitivity is improved to MSL 1 (Unlimited) compared to the original MSL 2A (4 Weeks).

MF-S350 (Bourns Inc.) provides an alternative from a different manufacturer while maintaining all critical electrical parameters. Post-trip resistance (R1) is specified at 40 mOhms maximum, which is lower than the SRP350's 50 mOhms maximum. This part is ROHS3 compliant and carries active product status. Approval agencies include cURus and TUV.

0ZSA0350FF1E (Bel Fuse Inc.) is a parametric equivalent offering from a third manufacturer. All electrical specifications match the SRP350 exactly. This part is ROHS3 compliant with active product status and MSL 1 (Unlimited) rating. Approval agencies include cURus and TUV.

Frequently Asked Questions (FAQ)

Q: Can SRP350F be used as a direct replacement for the obsolete SRP350?

A: Yes. SRP350F is electrically and mechanically identical to SRP350 across all specified parameters. Both are Littelfuse PolySwitch® SRP series components with 30V, 4.6A hold current, and identical physical dimensions. SRP350F is the recommended substitute due to active product status and improved compliance ratings.

Q: What is the difference between SRP350 and MF-S350 in terms of post-trip resistance?

A: MF-S350 specifies post-trip resistance (R1) at 40 mOhms maximum, while SRP350 specifies 50 mOhms maximum. This represents a tighter tolerance on the Bourns component. Both values fall within acceptable operating ranges for the 4.6A hold current application.

Q: Are all substitute parts ROHS3 compliant?

A: SRP350F, MF-S350, and 0ZSA0350FF1E are all ROHS3 compliant. The original SRP350 is RoHS non-compliant. If RoHS compliance is required for your application, any of the three substitutes are suitable.

Q: Do the substitute parts have the same moisture sensitivity rating as the SRP350?

A: No. SRP350 carries MSL 2A (4 Weeks), while SRP350F, MF-S350, and 0ZSA0350FF1E all carry MSL 1 (Unlimited). The substitutes offer improved moisture handling characteristics.

Q: Are there differences in approval agencies between the substitute parts?

A: SRP350F maintains the original approvals (CSA, TUV, UL). MF-S350 and 0ZSA0350FF1E carry cURus and TUV approvals. Verify that the approval agencies for your selected substitute meet your application requirements.

Q: Can these parts be used interchangeably in the same circuit board layout?

A: Yes. All substitute parts share identical physical dimensions (1.185" L x 0.522" W, 30.10mm x 13.25mm) and thickness (0.043", 1.10mm) in strap package configuration. No layout modifications are required.

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