SMAJ78C Equivalent & Substitute Parts

Part Overview

The SMAJ78C is a transient voltage suppressor (TVS) diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. This component operates with a reverse standoff voltage of 78V and provides clamping at 132.3V maximum with a peak pulse current of 3.2A. The part is classified as obsolete, necessitating identification of active equivalent alternatives that maintain electrical and mechanical compatibility for continued system support and new designs.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	78	V
Voltage - Breakdown (Min)	82.13	V
Voltage - Clamping (Max) @ Ipp	132.3	V
Current - Peak Pulse (10/1000µs)	3.2	A
Power - Peak Pulse	400	W
Operating Temperature Range	-65 to 150	°C (TJ)
Package / Case	DO-214AC, SMA	-
Mounting Type	Surface Mount	-
Type	Zener	-
Bidirectional Channels	1	-
RoHS Status	ROHS3 Compliant	-

Substitute Part Grouping Explanation

Substitution of the SMAJ78C is determined by strict alignment of the following electrical and mechanical parameters:

Critical Matching Parameters:

Reverse standoff voltage: 78V (nominal)
Breakdown voltage minimum: 82.13V to 86.7V range
Clamping voltage maximum: 126V to 139V range
Peak pulse current: 2.9A to 3.2A
Peak pulse power: 400W
Package: DO-214AC (SMA)
Mounting type: Surface Mount
Bidirectional channels: 1
Type: Zener diode

Substitute parts are grouped into two categories based on clamping voltage performance:

Group A (126V Clamping): SMAJ78CA (MDD), SMAJ78CA-E3/5A (Vishay), SMAJ78CA-E3/61 (Vishay), SMAJ78CA-M3/5A (Vishay), SMAJ78CA-M3/61 (Vishay), TV04A780JB-G (Comchip), ATV04A780JB-HF (Comchip)

Group B (139V Clamping): SMAJ78C (Taiwan Semiconductor Corporation)

All substitute parts maintain the 78V reverse standoff voltage, 400W peak pulse power rating, and DO-214AC package specification. Clamping voltage variations within the 126V to 139V range remain within acceptable operational margins for general-purpose transient suppression applications.

Parameter Comparison

Part Number	Manufacturer	Voltage - Reverse Standoff (V)	Voltage - Breakdown Min (V)	Voltage - Clamping Max @ Ipp (V)	Current - Peak Pulse (A)	Power - Peak Pulse (W)	Operating Temperature (°C)	Product Status	RoHS Status
SMAJ78C	Littelfuse Inc.	78	82.13	132.3	3.2	400	-65 to 150	Obsolete	ROHS3 Compliant
SMAJ78CA	MDD	78	86.7	126	3.2	400	-50 to 150	Active	ROHS3 Compliant
SMAJ78C	Taiwan Semiconductor Corporation	78	86.7	139	2.9	400	-55 to 150	Active	ROHS3 Compliant
SMAJ78CA-E3/5A	Vishay General Semiconductor - Diodes Division	78	86.7	126	3.2	400	-55 to 150	Active	ROHS3 Compliant
SMAJ78CA-E3/61	Vishay General Semiconductor - Diodes Division	78	86.7	126	3.2	400	-55 to 150	Active	ROHS3 Compliant
SMAJ78CA-M3/5A	Vishay General Semiconductor - Diodes Division	78	86.7	126	3.2	400	-55 to 150	Active	ROHS3 Compliant
SMAJ78CA-M3/61	Vishay General Semiconductor - Diodes Division	78	86.7	126	3.2	400	-55 to 150	Active	ROHS3 Compliant
TV04A780JB-G	Comchip Technology	78	86.7	126	3.17	400	-55 to 150	Active	ROHS3 Compliant
ATV04A780JB-HF	Comchip Technology	78	86.7	126	3.17	400	-55 to 150	Active	ROHS3 Compliant

Engineering Selection Recommendations

All listed substitute parts are active products with ROHS3 compliance and maintain the critical electrical parameters required for functional equivalence to the obsolete SMAJ78C. Selection between substitute options is determined by product availability, supply chain considerations, and specific application requirements.

For standard general-purpose applications: SMAJ78CA variants from Vishay (SMAJ78CA-E3/5A, SMAJ78CA-E3/61, SMAJ78CA-M3/5A, SMAJ78CA-M3/61) or Comchip (TV04A780JB-G) provide direct electrical compatibility with 126V clamping voltage and 3.2A peak pulse current.

For automotive-grade applications: ATV04A780JB-HF from Comchip Technology is qualified to AEC-Q101 automotive standards and provides equivalent electrical performance with automotive-grade certification.

For maximum clamping voltage margin: SMAJ78C from Taiwan Semiconductor Corporation offers 139V clamping voltage, providing additional transient suppression headroom compared to 126V alternatives, with active product status and ROHS3 compliance.

All substitute parts are packaged in DO-214AC (SMA) surface-mount configuration, maintaining mechanical compatibility with existing PCB layouts and assembly processes.

Frequently Asked Questions (FAQ)

Q: Can SMAJ78CA directly replace the obsolete Littelfuse SMAJ78C?

A: Yes. Both parts maintain 78V reverse standoff voltage, 400W peak pulse power, and DO-214AC package specification. The SMAJ78CA operates with 126V clamping voltage compared to the original 132.3V, representing a 4.8% reduction within acceptable operational margins for general-purpose transient suppression.

Q: What is the difference between 126V and 139V clamping voltage options?

A: The 126V clamping variants (SMAJ78CA series from Vishay and Comchip TV04A780JB-G) provide standard transient suppression performance. The 139V clamping variant (SMAJ78C from Taiwan Semiconductor Corporation) offers increased voltage margin during transient events. Selection depends on circuit design requirements and transient severity specifications.

Q: Are all substitute parts RoHS compliant?

A: Yes. All listed substitute parts carry ROHS3 compliance certification, meeting environmental and hazardous substance restrictions for commercial and industrial applications.

Q: What is the difference between standard and automotive-grade versions?

A: The ATV04A780JB-HF is qualified to AEC-Q101 automotive standards, suitable for automotive and harsh-environment applications. Standard versions (SMAJ78CA, TV04A780JB-G) are suitable for general industrial and commercial applications. Electrical performance is equivalent.

Q: Do operating temperature ranges differ between substitutes?

A: The original Littelfuse SMAJ78C operates from -65°C to 150°C. Most active substitutes operate from -55°C to 150°C, representing a 10°C reduction in minimum operating temperature. The MDD SMAJ78CA operates from -50°C to 150°C. Verify application requirements before selection if operation below -55°C is required.

Q: Are packaging and tape specifications identical across all substitutes?

A: All substitute parts use DO-214AC (SMA) surface-mount packaging. Tape & Reel (TR) packaging is standard across active alternatives. Confirm specific tape specifications with supplier documentation if custom reel configurations are required.

Q: What is the peak pulse current difference between 3.2A and 3.17A variants?

A: Comchip variants (TV04A780JB-G and ATV04A780JB-HF) specify 3.17A peak pulse current compared to 3.2A in other alternatives. This 0.09A difference (2.8% variation) remains within acceptable tolerance for general-purpose transient suppression applications.

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