SA18ARLG Equivalent & Substitute Parts

Part Overview

The SA18ARLG is a transient voltage suppressor (TVS) diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection applications. This axial-lead, through-hole component operates with an 18V reverse standoff voltage and provides 29.2V maximum clamping voltage at peak pulse current. The part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement.

Key Parameters

Parameter	Value
Voltage - Reverse Standoff (Typ)	18V
Voltage - Breakdown (Min)	20V
Voltage - Clamping (Max) @ Ipp	29.2V
Current - Peak Pulse (10/1000µs)	17.2A
Power - Peak Pulse	500W
Operating Temperature Range	-55°C ~ 150°C (TJ)
Mounting Type	Through Hole
Package / Case	DO-204AC (DO-15), Axial
Type	Zener
Unidirectional Channels	1

Substitute Part Grouping Explanation

Substitution eligibility for the SA18ARLG is determined by the following critical parameters:

Voltage - Reverse Standoff: 18V (required match)
Voltage - Clamping (Max) @ Ipp: 29.2V (required match)
Current - Peak Pulse (10/1000µs): 17.2A minimum
Power - Peak Pulse: 500W minimum
Mounting Type: Through Hole (required match)
Package / Case: DO-204AC (DO-15) or equivalent axial configuration (required match)
Type: Zener (required match)
Unidirectional Channels: 1 (required match)

Substitute parts are grouped into two categories:

Category A - Direct Electrical & Mechanical Equivalents: Parts matching all critical parameters with identical or superior current and power ratings, maintaining the same package footprint and thermal characteristics.

Category B - Higher-Performance Alternatives: Parts with superior current and power handling capabilities (SLD18U series) that maintain voltage specifications but operate in different package configurations (P600), suitable for applications requiring enhanced transient suppression capacity.

Parameter Comparison

Part Number	Manufacturer	Voltage - Reverse Standoff	Voltage - Clamping (Max) @ Ipp	Current - Peak Pulse (10/1000µs)	Power - Peak Pulse	Package / Case	Operating Temperature	Product Status
SA18ARLG	Littelfuse Inc.	18V	29.2V	17.2A	500W	DO-204AC (DO-15)	-55°C ~ 150°C	Obsolete
SA18A	Fairchild Semiconductor	18V	29.2V	17.5A	500W	DO-204AC (DO-15)	-55°C ~ 175°C	Obsolete
SA18A-E3/54	Vishay General Semiconductor	18V	29.2V	17.1A	500W	DO-204AC (DO-15)	-55°C ~ 175°C	Active
SA18AHE3/54	Vishay General Semiconductor	18V	29.2V	17.1A	500W	DO-204AC (DO-15)	-55°C ~ 175°C	Active
P5KE18A-AP	Micro Commercial Co	18V	29.2V	17.2A	500W	DO-204AC (DO-15)	-65°C ~ 175°C	Active
P5KE18A-BP	Micro Commercial Co	18V	29.2V	17.2A	500W	DO-204AC (DO-15)	-65°C ~ 175°C	Active
P5KE18A-TP	Micro Commercial Co	18V	29.2V	17.2A	500W	DO-204AC (DO-15)	-65°C ~ 175°C	Active
SAC18-AP	Micro Commercial Co	18V	28.8V	15A	500W	DO-204AC (DO-15)	-55°C ~ 175°C	Active
SLD18U-017	Littelfuse Inc.	18V	29.2V	174.7A	5000W	P600	-55°C ~ 175°C	Active
SLD18U-017-B	Littelfuse Inc.	18V	29.2V	174.7A	5000W	P600	-55°C ~ 175°C	Active
1N8159	Microchip Technology	18V	30.5V	4.92A	150W	Axial	-55°C ~ 175°C	Active

Engineering Selection Recommendations

Primary Substitutes (Direct Replacement - DO-204AC Package):

SA18A-E3/54, SA18AHE3/54, P5KE18A-AP, P5KE18A-BP, and P5KE18A-TP are direct electrical and mechanical equivalents suitable for one-to-one replacement of the SA18ARLG. These parts maintain identical voltage specifications (18V reverse standoff, 29.2V clamping) and current ratings (17.1A to 17.2A), with active product status ensuring long-term availability. SA18A-E3/54 and SA18AHE3/54 carry ROHS3 compliance and AEC-Q101 automotive qualification (SA18AHE3/54), providing enhanced reliability for critical applications. The P5KE18A series variants offer extended operating temperature range (-65°C to 175°C) compared to the original part (-55°C to 150°C).

Secondary Substitute (Reduced Performance - DO-204AC Package):

SAC18-AP operates within the same package and mounting configuration but with reduced peak pulse current (15A versus 17.2A) and slightly lower clamping voltage (28.8V versus 29.2V). This part is suitable only for applications where the lower current rating does not compromise circuit protection requirements.

Higher-Performance Alternative (Different Package - P600):

SLD18U-017 and SLD18U-017-B are manufacturer-recommended alternatives from Littelfuse Inc. with significantly enhanced current handling (174.7A) and power dissipation (5000W). These parts maintain identical voltage specifications but require PCB layout modification due to the P600 package configuration. Both variants carry AEC-Q101 automotive qualification and active product status. Selection of this alternative is appropriate for applications requiring superior transient suppression capacity or higher reliability margins.

Not Recommended:

1N8159 exhibits reduced peak pulse current (4.92A) and power rating (150W), making it unsuitable for applications matching the SA18ARLG performance envelope. Additionally, this part carries RoHS non-compliant status.

Frequently Asked Questions (FAQ)

Q: Can SA18A-E3/54 be used as a direct replacement for SA18ARLG?

A: Yes. SA18A-E3/54 maintains identical voltage specifications (18V reverse standoff, 29.2V clamping) and equivalent current rating (17.1A), operates in the same DO-204AC package, and is actively manufactured. The part is ROHS3 compliant and suitable for direct PCB substitution.

Q: What is the difference between P5KE18A-AP, P5KE18A-BP, and P5KE18A-TP?

A: These three variants are electrically identical, all manufactured by Micro Commercial Co with matching voltage and current specifications. The suffix designations (AP, BP, TP) indicate different packaging or tape configurations. All three are suitable for direct replacement of SA18ARLG.

Q: Why would I select SLD18U-017 over SA18A-E3/54?

A: SLD18U-017 provides 10 times higher peak pulse current (174.7A versus 17.1A) and 10 times higher power dissipation (5000W versus 500W). Selection is appropriate for applications requiring enhanced transient suppression capacity, higher reliability margins, or exposure to more severe overvoltage events. The P600 package requires PCB layout modification.

Q: Is SAC18-AP a suitable replacement?

A: SAC18-AP is electrically compatible but operates at reduced performance levels. Peak pulse current is 15A (versus 17.2A) and clamping voltage is 28.8V (versus 29.2V). This part is suitable only if the application does not require the full current and voltage specifications of the original SA18ARLG.

Q: What compliance certifications should I verify for critical applications?

A: For automotive or high-reliability applications, prioritize parts carrying AEC-Q101 qualification (SA18AHE3/54, SLD18U-017, SLD18U-017-B). For general industrial applications, ROHS3 compliance is standard across active substitutes. Verify REACH status for supply chain compliance; all listed substitutes carry REACH Unaffected status.

Q: Can I use 1N8159 as a substitute?

A: No. 1N8159 exhibits insufficient peak pulse current (4.92A) and power rating (150W) relative to the SA18ARLG specification (17.2A, 500W). Additionally, this part is RoHS non-compliant. Selection would compromise circuit protection performance.

Q: What is the thermal operating range difference between SA18ARLG and its substitutes?

A: SA18ARLG operates from -55°C to 150°C. Most active substitutes extend the upper limit to 175°C, providing improved thermal margin. P5KE18A series variants extend the lower limit to -65°C. Verify thermal requirements for your specific application before selection.

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