SA78-B Transient Voltage Suppressor (TVS) Equivalent & Substitute Parts

Part Overview

The SA78-B is a unidirectional Zener-type transient voltage suppressor diode manufactured by Littelfuse Inc., designed for telecom applications. This through-hole component features a 78V reverse standoff voltage with 126V maximum clamping voltage and 4A peak pulse current capability in a DO-204AC (DO-15) axial package.

The SA78-B is classified as obsolete. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support ongoing production or repair requirements for systems utilizing this component.

Substiute Parts

SA78-B

Littelfuse Inc.In Stock: 687SA78-B Datasheet

Current PartRFQ

SA78A

Taiwan Semiconductor CorporationIn Stock: 884SA78A Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the SA78-B is determined by strict equivalence across the following critical electrical and mechanical parameters:

Electrical Equivalence Criteria:

• Voltage - Reverse Standoff (Typ): 78V
• Voltage - Breakdown (Min): 86.7V
• Voltage - Clamping (Max) @ Ipp: 126V
• Current - Peak Pulse (10/1000µs): ≥ 4A
• Power - Peak Pulse: 500W
• Unidirectional Channels: 1
• Type: Zener

Mechanical Equivalence Criteria:

• Package / Case: DO-204AC (DO-15)
• Mounting Type: Through Hole
• Operating Temperature Range: Must encompass or match the original specification

The SA78A meets all electrical parameters with a peak pulse current of 4.1A, exceeding the minimum 4A requirement. Both components share identical voltage ratings, power dissipation, package configuration, and mounting type. The SA78A operates across -55°C to 175°C, which overlaps the SA78-B operating range of -65°C to 175°C.

Parameter Comparison

Engineering Selection Recommendations

The SA78A is a direct functional substitute for the SA78-B based on electrical and mechanical parameter equivalence. The SA78A is manufactured by Taiwan Semiconductor Corporation and maintains active product status, ensuring ongoing availability and supply chain support.

Compliance Considerations:

Both components are RoHS compliant. The SA78A carries ROHS3 compliance certification and is REACH unaffected, meeting current environmental and regulatory standards. The SA78-B, classified as obsolete, presents long-term supply risk; the SA78A addresses this constraint while maintaining full electrical and mechanical compatibility.

Temperature Operating Range:

The SA78A operates across -55°C to 175°C, compared to the SA78-B range of -65°C to 175°C. For applications requiring operation below -55°C, the SA78-B specification must be retained. For standard industrial and telecom applications operating within -55°C to 175°C, the SA78A is suitable.

Peak Pulse Current:

The SA78A provides 4.1A peak pulse current, exceeding the SA78-B specification of 4A. This higher rating provides additional margin in transient suppression applications without introducing incompatibility.

Frequently Asked Questions (FAQ)

Q: Can the SA78A directly replace the SA78-B in existing designs?

A: Yes, for applications operating within the -55°C to 175°C temperature range. Both components share identical voltage ratings (78V standoff, 126V clamping), peak pulse power (500W), package configuration (DO-204AC), and mounting type (through hole). The SA78A peak pulse current of 4.1A exceeds the SA78-B requirement of 4A.

Q: What is the primary reason to substitute the SA78-B?

A: The SA78-B is classified as obsolete. The SA78A is an active product with confirmed supply availability, ensuring design continuity and production support.

Q: Are there packaging differences between SA78-B and SA78A?

A: Both components use the DO-204AC (DO-15) axial through-hole package. The SA78-B is supplied in standard packaging, while the SA78A is available in Tape & Reel (TR) format. Both are mechanically and electrically compatible for PCB assembly.

Q: Do both parts meet RoHS requirements?

A: Yes. The SA78-B is RoHS compliant. The SA78A is ROHS3 compliant and REACH unaffected, meeting current environmental standards.

Q: What is the temperature operating range difference?

A: The SA78-B operates from -65°C to 175°C (TJ). The SA78A operates from -55°C to 175°C (TJ). For applications requiring operation below -55°C, the SA78-B specification must be maintained. For standard industrial and telecom applications, the SA78A is suitable.

Q: Is the higher peak pulse current of SA78A (4.1A vs. 4A) a concern?

A: No. The higher rating provides additional transient suppression margin and does not introduce incompatibility. The component remains functionally equivalent for all applications designed for the SA78-B.

Q: Can the SA78A be used in telecom applications?

A: Yes. The SA78A is rated for general-purpose applications and meets all electrical requirements for telecom transient voltage suppression. The SA78-B was specifically designated for telecom; the SA78A provides equivalent performance across this application domain.