Equivalent & Substitute Parts for 1812L050ZRT

Part Overview

The 1812L050ZRT is a Polymeric PTC Resettable Fuse manufactured by Littelfuse Inc., rated at 15V with a 500 mA hold current. This component is classified as Obsolete, necessitating identification of equivalent and substitute parts for ongoing design support and procurement. The part is housed in a 1812 (4532 Metric) surface mount package with concave geometry and meets ROHS3 compliance requirements.

Key Parameters

Parameter	Value
Manufacturer Part Number	1812L050ZRT
Manufacturer	Littelfuse Inc.
Series	POLY-FUSE®, 1812L
Product Status	Obsolete
Type	Polymeric
Voltage - Max	15V
Current - Hold (Ih) (Max)	500 mA
Current - Trip (It)	1 A
Current - Max	100 A
Time to Trip	150 ms
Resistance - Initial (Ri) (Min)	150 mOhms
Resistance - Post Trip (R1) (Max)	1 Ohms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package / Case	1812 (4532 Metric), Concave
Size / Dimension	0.179" L x 0.128" W (4.55mm x 3.24mm)
Thickness (Max)	0.030" (0.75mm)
Approval Agency	cURus, TUV
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution of the 1812L050ZRT is determined by the following critical parameters:

Electrical Parameters:

Voltage rating (maximum voltage the fuse can withstand)
Current hold (Ih) specification (500 mA)
Current trip (It) specification (1 A)
Time to trip (150 ms)
Initial and post-trip resistance values

Mechanical Parameters:

Package type: 1812 (4532 Metric), Concave geometry
Surface mount mounting type
Physical dimensions and thickness compatibility

Compliance Parameters:

ROHS3 compliance requirement
Approval agencies (cURus, TUV minimum)

Substitute parts are grouped into three categories:

Direct Manufacturer Equivalents - Same electrical specifications, same voltage rating (15V), same current hold (500 mA), active product status
Parametric Equivalents - Identical electrical and mechanical specifications but different voltage ratings (16V or 24V) or different manufacturers
Upgrade Parts - Higher voltage rating (30V) with identical current and thermal characteristics

Parameter Comparison

Part Number	Manufacturer	Voltage - Max	Current - Hold (Ih)	Current - Trip (It)	Time to Trip	Ri (Min)	R1 (Max)	Package	Thickness (Max)	Product Status	Approval Agency
1812L050ZRT	Littelfuse Inc.	15V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.030" (0.75mm)	Obsolete	cURus, TUV
1812L050PR	Littelfuse Inc.	15V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.030" (0.75mm)	Active	cURus, TUV
MF-MSMF050-2	Bourns Inc.	15V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.033" (0.85mm)	Active	cURus, TUV
PTS181216V050	Eaton - Electronics Division	16V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.027" (0.68mm)	Active	cURus, TUV
FSMD050-R	RFE/Fuzetec	16V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.026" (0.65mm)	Active	cUL, TUV, UL
MINISMDC050F-2	Littelfuse	24V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.024" (0.62mm)	Active	CSA, TUV, UL
FSMD050-30-R	RFE/Fuzetec	30V	500 mA	1 A	150 ms	150 mOhms	1 Ohms	1812 (4532 Metric), Concave	0.030" (0.75mm)	Active	cUL, TUV, UL

Engineering Selection Recommendations

Primary Recommendation: 1812L050PR

The 1812L050PR is the direct equivalent replacement for the obsolete 1812L050ZRT. Both parts are manufactured by Littelfuse Inc., share identical electrical specifications (15V, 500 mA hold current), and are housed in the same 1812 (4532 Metric) concave package. The 1812L050PR maintains Active product status with full ROHS3 compliance and cURus/TUV approvals. This part is available in high volume (128,236 pcs in stock) and is the preferred choice for direct substitution.

Secondary Recommendation: MF-MSMF050-2

The MF-MSMF050-2 from Bourns Inc. provides parametric equivalence with identical electrical characteristics (15V, 500 mA hold current, 1 A trip current). This part is Active, ROHS3 compliant, and carries cURus/TUV approvals. The thickness specification (0.033" vs. 0.030") is marginally higher but remains within typical PCB assembly tolerances. This option is suitable when Littelfuse parts are unavailable.

Alternative Recommendations for Higher Voltage Applications:

PTS181216V050 (Eaton): 16V rating, Active status, cURus/TUV approved. Suitable for applications requiring higher voltage margin.
FSMD050-R (RFE/Fuzetec): 16V rating, Active status, expanded approvals (cUL, TUV, UL). Thinner profile (0.026") may benefit space-constrained designs.
MINISMDC050F-2 (Littelfuse): 24V rating, Active status, expanded approvals (CSA, TUV, UL). Thinnest profile (0.024") for high-density applications.
FSMD050-30-R (RFE/Fuzetec): 30V rating, Active status, expanded approvals (cUL, TUV, UL). Upgrade option for maximum voltage headroom.

All recommended substitutes maintain the 500 mA hold current, 1 A trip current, 150 ms trip time, and 1812 surface mount package geometry. Selection should be based on circuit voltage requirements, available inventory, and approval agency requirements for the target application.

Frequently Asked Questions (FAQ)

Q: Can I use a higher voltage-rated fuse as a direct replacement?

A: Yes, within the constraints of your circuit design. A 16V, 24V, or 30V rated fuse can replace the 15V 1812L050ZRT in applications where the circuit voltage does not exceed the fuse rating. The electrical trip characteristics (500 mA hold, 1 A trip) remain identical. However, verify that your circuit voltage does not exceed the substitute part's maximum rating.

Q: What is the difference between the 1812L050ZRT and 1812L050PR?

A: Both parts are identical in electrical and mechanical specifications. The primary difference is product status: 1812L050ZRT is Obsolete, while 1812L050PR is Active. The 1812L050PR is the direct replacement manufactured by Littelfuse Inc. for the discontinued 1812L050ZRT.

Q: Are all substitute parts compatible with my PCB layout?

A: All substitute parts use the 1812 (4532 Metric) surface mount package with concave geometry. Physical dimensions (0.179" L x 0.128" W) are identical across all options. Thickness varies slightly (0.024" to 0.033"), which is typically accommodated by standard PCB assembly processes. Verify your specific PCB footprint and reflow profile compatibility with your assembly partner.

Q: Which substitute part has the best availability?

A: MINISMDC050F-2 has the highest inventory (805,200 pcs), followed by 1812L050PR (128,236 pcs). Both are Littelfuse products with Active status and immediate availability.

Q: Do all substitute parts meet ROHS3 compliance?

A: Yes, all substitute parts listed are ROHS3 compliant. Approval agencies vary: the original part requires cURus/TUV minimum; substitute parts maintain these certifications or expand them (CSA, cUL, UL).

Q: What is the significance of the 150 ms time-to-trip specification?

A: The 150 ms time-to-trip is a thermal response characteristic that determines how quickly the fuse responds to overcurrent conditions. All substitute parts maintain this specification, ensuring consistent circuit protection behavior.

Q: Can I substitute a Bourns MF-MSMF050-2 for the Littelfuse original?

A: Yes. The MF-MSMF050-2 provides parametric equivalence with identical electrical specifications (15V, 500 mA hold current). Both are ROHS3 compliant with cURus/TUV approvals. The thickness is 0.033" versus 0.030" for the original, a difference that does not affect functionality in standard surface mount applications.

Q: What does "Polymeric" type mean?

A: Polymeric PTC (Positive Temperature Coefficient) resettable fuses are self-resetting overcurrent protection devices. Unlike traditional fuses, they automatically reset after the overcurrent condition is removed, eliminating the need for component replacement.

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