SMF78AT1G Equivalent & Substitute Parts

Part Overview

The SMF78AT1G is a unidirectional transient voltage suppressor (TVS) diode manufactured by onsemi, designed for general-purpose overvoltage protection in surface-mount applications. Specified with a 78V reverse standoff voltage and 126V maximum clamping voltage, this component operates across the industrial temperature range of -55°C to 150°C in a compact SOD-123FL package.

The SMF78AT1G is classified as obsolete. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for new production runs and field replacements.

Key Parameters

Parameter	Value
Manufacturer Part Number	SMF78AT1G
Manufacturer	onsemi
Category	Transient Voltage Suppressors (TVS)
Type	Zener
Unidirectional Channels	1
Voltage - Reverse Standoff (Typ)	78V
Voltage - Breakdown (Min)	86.7V
Voltage - Clamping (Max) @ Ipp	126V
Current - Peak Pulse (10/1000µs)	1.4A
Power - Peak Pulse	200W
Operating Temperature	-55°C ~ 150°C (TJ)
Mounting Type	Surface Mount
Package / Case	SOD-123F
Moisture Sensitivity Level (MSL)	1 (Unlimited)
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the SMF78AT1G is determined by the following critical electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - Reverse Standoff (Typ): 78V
Voltage - Clamping (Max) @ Ipp: 126V
Current - Peak Pulse (10/1000µs): minimum 1.4A
Power - Peak Pulse: 200W
Package / Case: SOD-123F or equivalent surface-mount footprint
Unidirectional Channels: 1
Operating Temperature Range: -55°C to 150°C minimum

Direct Equivalent: SMF78A (Meritek) matches all critical electrical parameters with identical voltage ratings and package configuration. This part is classified as active and represents the primary substitute.

Similar Voltage Series: Parts including SMF54A, SMF24A, SMF22A, SMF20A, and SMF18A operate at different voltage ratings and are listed as similar alternatives. These parts share the same 200W power rating, SOD-123F package family, and general-purpose TVS application profile but are not electrical equivalents due to different voltage specifications.

Parameter Comparison

Parameter	SMF78AT1G (onsemi)	SMF78A (Meritek)	SMF54A (Diotec)	SMF24A (MDD)	SMF22A (MDD)
Voltage - Reverse Standoff (Typ)	78V	78V	54V	24V	22V
Voltage - Breakdown (Min)	86.7V	86.7V	60V	26.7V	24.4V
Voltage - Clamping (Max) @ Ipp	126V	126V	87.1V	38.9V	35.5V
Current - Peak Pulse (10/1000µs)	1.4A	1.59A	2.3A	5.1A	5.6A
Power - Peak Pulse	200W	200W	200W	200W	200W
Operating Temperature	-55°C ~ 150°C	-55°C ~ 150°C	-50°C ~ 150°C	-55°C ~ 150°C	-55°C ~ 150°C
Package / Case	SOD-123F	SOD-123FL	SOD-123F	SOD-123F, SMF	SOD-123F, SMF
Type	Zener	Zener	Zener	Zener	Zener
Unidirectional Channels	1	1	1	1	1
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Substitute - SMF78A (Meritek): SMF78A is the direct electrical equivalent to SMF78AT1G. It maintains identical voltage specifications (78V standoff, 126V clamping) and operating temperature range (-55°C to 150°C). The part is currently in active production status with ROHS3 compliance certification. Peak pulse current is slightly higher at 1.59A compared to 1.4A, providing improved margin. Packaging is SOD-123FL, compatible with SOD-123F footprints. This part is recommended as the primary replacement for direct substitution.

Alternative Substitutes - Voltage-Specific Selection: SMF54A, SMF24A, SMF22A, SMF20A, and SMF18A are active alternatives suitable only when circuit design permits operation at lower voltage ratings. Selection among these parts depends on the specific overvoltage protection threshold required by the application. All alternatives maintain 200W power rating and surface-mount SOD-123F package compatibility. All listed alternatives carry ROHS3 compliance.

Compliance Considerations: All recommended substitute parts are ROHS3 compliant and carry REACH unaffected or available-upon-request status, meeting current environmental and regulatory requirements for electronics manufacturing.

Frequently Asked Questions (FAQ)

Q: Can SMF78A directly replace SMF78AT1G without circuit modification? A: Yes. SMF78A is a direct electrical equivalent with matching voltage ratings (78V standoff, 126V clamping), identical power rating (200W), and compatible operating temperature range (-55°C to 150°C). The SOD-123FL package is footprint-compatible with SOD-123F. No circuit changes are required.

Q: What is the difference between SMF78A and the lower-voltage alternatives listed? A: SMF78A maintains the 78V reverse standoff voltage specification of the original part. Lower-voltage alternatives (SMF54A at 54V, SMF24A at 24V, SMF22A at 22V) are suitable only for applications requiring protection at those specific voltage thresholds. Voltage selection must match the circuit's overvoltage protection requirement.

Q: Are all substitute parts RoHS compliant? A: Yes. All listed substitute parts carry ROHS3 compliance certification, meeting current environmental standards for electronics manufacturing and assembly.

Q: Does the slightly higher peak pulse current in SMF78A (1.59A vs. 1.4A) affect compatibility? A: No. The higher peak pulse current in SMF78A provides additional margin and does not negatively impact circuit performance. The part remains suitable for applications designed for the original 1.4A specification.

Q: What is the significance of the SOD-123FL vs. SOD-123F package designation? A: Both designations refer to the same physical footprint and are mechanically and electrically compatible. SOD-123FL and SOD-123F are interchangeable in surface-mount assembly processes.

Q: Why is SMF78AT1G listed as obsolete? A: Obsolete status indicates the part is no longer manufactured by onsemi. SMF78A from Meritek provides functional continuity for existing designs and new production requirements.

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