SA18 Transient Voltage Suppressor (TVS) Diode - Equivalent & Substitute Parts

Part Overview

The SA18 is an 18V Zener-type transient voltage suppressor diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection applications. The device features a 30.66V maximum clamping voltage at peak pulse current and is housed in a DO-204AC (DO-15) axial through-hole package. The SA18 is classified as obsolete, making equivalent substitute parts necessary for ongoing design support and procurement.

Substiute Parts

SA18

Littelfuse Inc.In Stock: 637SA18 Datasheet

Current PartRFQ

SA18A

Fairchild SemiconductorIn Stock: 7654SA18A Datasheet

DirectRFQ

SA18A-AP

Micro Commercial CoIn Stock: 847SA18A-AP Datasheet

MFR RecommendedRFQ

SA18A-BP

Micro Commercial CoIn Stock: 1265SA18A-BP Datasheet

MFR RecommendedRFQ

SA18A-E3/54

Vishay General Semiconductor - Diodes DivisionIn Stock: 1715SA18A-E3/54 Datasheet

MFR RecommendedRFQ

SA18A-TP

Micro Commercial CoIn Stock: 941SA18A-TP Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the SA18 are qualified based on the following critical parameters that determine functional equivalence:

• Voltage - Reverse Standoff (Typ): 18V
• Voltage - Clamping (Max) @ Ipp: 29.2V to 30.66V range
• Current - Peak Pulse (10/1000µs): 17.1A to 17.5A
• Power - Peak Pulse: 500W
• Operating Temperature Range: -55°C to 175°C (TJ)
• Package / Case: DO-204AC or DO-15 axial through-hole
• Type: Zener unidirectional

All substitute parts maintain identical standoff voltage, peak pulse power rating, and operating temperature specifications. Clamping voltage and peak pulse current remain within acceptable tolerance bands for direct substitution in the same circuit application.

Parameter Comparison

Engineering Selection Recommendations

For new designs and ongoing procurement, active product status substitutes are preferred. SA18A-E3/54 (Vishay) is recommended as the primary substitute due to active product status, ROHS3 compliance, and DO-204AC package availability matching the original SA18 footprint. SA18A-AP, SA18A-BP, and SA18A-TP (Micro Commercial Co) are functionally equivalent alternatives with active status and REACH compliance, though available only in DO-15 package configuration.

SA18A (Fairchild) maintains full electrical equivalence but carries obsolete product status, limiting its suitability for new applications requiring long-term component availability.

All substitute parts satisfy the electrical requirements of the original SA18 within specified parameter tolerances and maintain identical thermal operating range and power dissipation characteristics.

Frequently Asked Questions (FAQ)

Q: Can SA18A-E3/54 directly replace SA18 in existing designs?

A: Yes. SA18A-E3/54 maintains identical reverse standoff voltage (18V), peak pulse power (500W), and operating temperature range (-55°C to 175°C). The clamping voltage is 29.2V versus the original 30.66V, and peak pulse current is 17.1A versus 17.5A—both within acceptable tolerance for general-purpose transient suppression applications. The DO-204AC package is footprint-compatible with the original SA18.

Q: What is the difference between SA18A-AP, SA18A-BP, and SA18A-TP?

A: These three Micro Commercial Co variants (SA18A-AP, SA18A-BP, SA18A-TP) are electrically identical with matching specifications: 18V standoff voltage, 29.2V clamping voltage, 17.5A peak pulse current, and 500W peak pulse power. The designations reflect different packaging or distribution channels. All three are active products with REACH compliance. Selection between them depends on packaging availability and supplier inventory.

Q: Does package type affect substitution compatibility?

A: Package type affects PCB footprint compatibility. The original SA18 is available in DO-204AC (DO-15) axial through-hole. SA18A-E3/54 maintains DO-204AC availability for direct footprint compatibility. SA18A-AP, SA18A-BP, and SA18A-TP are available only in DO-15 package. Both DO-204AC and DO-15 are axial through-hole variants with identical electrical performance; footprint verification is required for PCB layout compatibility.

Q: Are all substitutes RoHS compliant?

A: SA18A-E3/54 (Vishay) is explicitly ROHS3 compliant. RoHS status for SA18A (Fairchild) and the Micro Commercial Co variants (SA18A-AP, SA18A-BP, SA18A-TP) is not specified in the provided data. Compliance verification with component suppliers is recommended for applications requiring RoHS certification.

Q: Why is SA18 classified as obsolete?

A: The SA18 is listed as obsolete by Littelfuse Inc., indicating discontinued production. Active substitute parts ensure design continuity and long-term component availability for maintenance and new production builds.