SMAJ78 Equivalent & Substitute Parts

Part Overview

The SMAJ78 is a unidirectional Zener transient voltage suppressor (TVS) diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. The device features a 78V reverse standoff voltage, 132.3V maximum clamping voltage, and 3.2A peak pulse current rating in a DO-214AC (SMA) package. The SMAJ78 is currently listed as obsolete, making equivalent substitute parts necessary for ongoing design support and procurement.

Substiute Parts

SMAJ78

Littelfuse Inc.In Stock: 839SMAJ78 Datasheet

Current PartRFQ

SMAJ78A

MeritekIn Stock: 1389SMAJ78A Datasheet

MFR RecommendedRFQ

SMAJ78A

MeritekIn Stock: 1389SMAJ78A Datasheet

MFR RecommendedRFQ

SMAJ78A-TP

Micro Commercial CoIn Stock: 6050SMAJ78A-TP Datasheet

MFR RecommendedRFQ

SMAJ78AE3/TR13

Microchip TechnologyIn Stock: 972SMAJ78AE3/TR13 Datasheet

MFR RecommendedRFQ

SMAJ78E3/TR13

Microchip TechnologyIn Stock: 1170SMAJ78E3/TR13 Datasheet

MFR RecommendedRFQ

TV04A780J-G

Comchip TechnologyIn Stock: 1231TV04A780J-G Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the SMAJ78 is determined by the following critical parameters:

• Voltage - Reverse Standoff: Must be 78V (±tolerance as specified by manufacturer)
• Package / Case: Must be DO-214AC (SMA) for mechanical and electrical compatibility
• Unidirectional Channels: Must be 1 (single channel)
• Type: Must be Zener TVS diode
• RoHS Status: Must maintain ROHS3 compliance

Secondary parameters that may vary within acceptable ranges:

• Voltage - Clamping (Max) @ Ipp: 126V to 139V (within typical TVS tolerance bands)
• Current - Peak Pulse: 2.2A to 4A (device-dependent rating variation)
• Power - Peak Pulse: 400W to 500W (correlates with current rating)
• Operating Temperature: -55°C to -65°C minimum; 150°C to 175°C maximum

All identified substitutes maintain the core 78V standoff voltage specification and DO-214AC package requirement, ensuring direct functional equivalence in circuit applications.

Parameter Comparison

Engineering Selection Recommendations

All listed substitute parts maintain active product status and ROHS3 compliance, providing long-term availability and regulatory alignment compared to the obsolete SMAJ78.

For applications requiring the original clamping voltage specification of 132.3V, no direct substitute with identical clamping voltage is available. The closest alternative is SMAJ78E3/TR13 (Microchip Technology) at 139V clamping voltage, which exceeds the original specification by 6.7V.

For applications with standard clamping voltage tolerance, SMAJ78A (Meritek), SMAJ78A-TP (Micro Commercial Co), SMAJ78AE3/TR13 (Microchip Technology), and TV04A780J-G (Comchip Technology) all provide 126V clamping voltage, representing a 4.3V reduction from the original specification.

SMAJ78AE3/TR13 offers the highest peak pulse current rating (4A) and power dissipation (500W), providing additional margin for high-energy transient events. SMAJ78A-TP offers the widest operating temperature range (-55°C to 175°C), suitable for extended thermal environments.

Frequently Asked Questions (FAQ)

Q: Can SMAJ78 substitutes be used interchangeably in existing designs?

A: Yes, all listed substitutes maintain the 78V reverse standoff voltage and DO-214AC package specification. However, clamping voltage variations (126V to 139V versus the original 132.3V) must be evaluated against circuit protection requirements. Designs with tight clamping voltage tolerances should confirm compatibility with the substitute's specified range.

Q: What is the difference between SMAJ78A and SMAJ78AE3/TR13?

A: Both maintain 78V standoff voltage and 126V clamping voltage. SMAJ78AE3/TR13 provides higher peak pulse current (4A versus 3.17A) and power dissipation (500W versus 400W). SMAJ78AE3/TR13 is supplied in Tape & Reel packaging, while SMAJ78A availability varies by supplier. Selection depends on current handling requirements and packaging preference.

Q: Why does SMAJ78E3/TR13 have a higher clamping voltage (139V)?

A: SMAJ78E3/TR13 is a variant within the SMAJ78 series with different internal design parameters. The 139V clamping voltage represents a different performance point within the 78V standoff voltage family. This part is suitable for applications where slightly higher clamping voltage is acceptable or beneficial.

Q: Are all substitutes ROHS3 compliant?

A: Yes, all listed substitute parts are ROHS3 compliant, meeting current environmental and regulatory requirements for electronic component manufacturing and use.

Q: What packaging options are available for substitutes?

A: All substitutes are supplied in DO-214AC (SMA) surface-mount package. SMAJ78A-TP, SMAJ78AE3/TR13, SMAJ78E3/TR13, and TV04A780J-G are available in Tape & Reel (TR) packaging for automated assembly. SMAJ78A availability in specific packaging formats should be confirmed with the supplier.

Q: Which substitute offers the best thermal performance?

A: SMAJ78A-TP offers the widest operating temperature range (-55°C to 175°C ambient), providing the greatest thermal margin for high-temperature applications. SMAJ78AE3/TR13 and SMAJ78E3/TR13 specify -65°C to 150°C junction temperature, matching the original SMAJ78 lower temperature limit.