SMAJ18C Transient Voltage Suppressor (TVS) Diode - Equivalent & Substitute Parts

Part Overview

The SMAJ18C is a bidirectional Zener transient voltage suppressor diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. The device features an 18V reverse standoff voltage with a 30.66V maximum clamping voltage at peak pulse current, housed in a DO-214AC (SMA) package. The original Littelfuse SMAJ18C is classified as obsolete, necessitating identification of functionally equivalent active alternatives that maintain electrical and mechanical compatibility for new designs and production continuity.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	18	V
Voltage - Breakdown (Min)	18.95	V
Voltage - Clamping (Max) @ Ipp	30.66	V
Current - Peak Pulse (10/1000µs)	13.7	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 eligibility for the SMAJ18C is determined by strict alignment of the following electrical and mechanical parameters:

Reverse standoff voltage must be 18V (nominal). Breakdown voltage minimum must fall within 18.95V to 20V range. Clamping voltage at peak pulse current must not exceed 32.2V maximum. Peak pulse current must be 13.7A or higher. Peak pulse power rating must be 400W minimum. Package and case must be DO-214AC (SMA) for mechanical and thermal compatibility. Mounting type must be surface mount. Device type must be Zener bidirectional with single channel configuration. Operating temperature range must support -55°C to 150°C minimum (original specification -65°C to 150°C is the most stringent). RoHS3 compliance is required.

Substitute parts are grouped into two categories: direct electrical equivalents from active manufacturers (MDD, Vishay, Comchip Technology, Taiwan Semiconductor Corporation) with identical or tighter electrical specifications, and functionally compatible alternatives that meet all substitution criteria while maintaining design margin.

Parameter Comparison

Part Number	Manufacturer	Vwm (V)	Vbr Min (V)	Vc Max @ Ipp (V)	Ipp (A)	Ppk (W)	Tj Range (°C)	Status
SMAJ18C	Littelfuse Inc.	18	18.95	30.66	13.7	400	-65 to 150	Obsolete
SMAJ18C	Taiwan Semiconductor Corporation	18	20	32.2	12.4	400	-55 to 150	Active
SMAJ18CA	MDD	18	20	29.2	13.7	400	-50 to 150	Active
SMAJ18CA-E3/5A	Vishay General Semiconductor - Diodes Division	18	20	29.2	13.7	400	-55 to 150	Active
SMAJ18CA-E3/61	Vishay General Semiconductor - Diodes Division	18	20	29.2	13.7	400	-55 to 150	Active
SMAJ18CA-M3/5A	Vishay General Semiconductor - Diodes Division	18	20	29.2	13.7	400	-55 to 150	Active
SMAJ18CA-M3/61	Vishay General Semiconductor - Diodes Division	18	20	29.2	13.7	400	-55 to 150	Active
TV04A180JB-G	Comchip Technology	18	20	29.2	13.7	400	-55 to 150	Active

Engineering Selection Recommendations

All identified substitute parts maintain active product status with ROHS3 compliance and REACH unaffected certification, ensuring regulatory compliance and supply chain continuity. The Vishay TransZorb® series (SMAJ18CA-E3/5A, SMAJ18CA-E3/61, SMAJ18CA-M3/5A, SMAJ18CA-M3/61) and Comchip TV04A180JB-G offer superior clamping voltage performance (29.2V) compared to the original specification (30.66V), providing enhanced transient suppression margin. The MDD SMAJ18CA variant delivers identical electrical performance with active status. The Taiwan Semiconductor Corporation SMAJ18C maintains the original part number designation with active availability, though peak pulse current is reduced to 12.4A.

For applications requiring maximum design margin and established supply relationships, Vishay variants with -55°C to 150°C operating range are preferred. For cost-optimized procurement with equivalent performance, MDD SMAJ18CA or Comchip TV04A180JB-G are suitable. All substitutes are mechanically compatible in DO-214AC (SMA) surface-mount footprints.

Frequently Asked Questions (FAQ)

Q: Can SMAJ18CA directly replace the obsolete Littelfuse SMAJ18C?

A: Yes. SMAJ18CA from MDD and Vishay variants meet all electrical substitution criteria: 18V reverse standoff, 20V minimum breakdown, 29.2V clamping voltage, 13.7A peak pulse current, and 400W peak power. All are housed in DO-214AC (SMA) packages with identical footprints and thermal characteristics.

Q: What is the difference between Vishay SMAJ18CA-E3/5A and SMAJ18CA-M3/5A?

A: Both variants share identical electrical specifications (18V Vwm, 29.2V clamping, 13.7A Ipp, 400W peak power) and operating temperature range (-55°C to 150°C). The designations reflect different packaging configurations and tape reel specifications. Selection depends on procurement and assembly requirements.

Q: Why does the Taiwan Semiconductor SMAJ18C show 12.4A peak pulse current instead of 13.7A?

A: This represents a different manufacturing variant with reduced peak pulse current specification. While it maintains 18V reverse standoff and 400W peak power, the lower current rating may not be suitable for applications requiring the full 13.7A pulse capability of the original design.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All identified substitutes carry ROHS3 Compliant certification and REACH Unaffected status, meeting current environmental and regulatory requirements.

Q: What is the operating temperature difference between the original and substitutes?

A: The original Littelfuse SMAJ18C specifies -65°C to 150°C. Most active substitutes (Vishay, Comchip) support -55°C to 150°C, which is acceptable for most applications. The MDD variant supports -50°C to 150°C. Verify application requirements before selection if operation below -55°C is necessary.

Q: Can these parts be used interchangeably on existing PCBs?

A: Yes. All substitute parts use the DO-214AC (SMA) package with identical mechanical dimensions, pin spacing, and thermal characteristics. No PCB layout modifications are required for direct substitution.

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