SMAJ18A-TP Equivalent & Substitute Parts

Part Overview

The SMAJ18A-TP is an active-status Transient Voltage Suppressor (TVS) diode manufactured by Micro Commercial Co, designed for general-purpose overvoltage protection in surface-mount applications. This unidirectional Zener diode operates with an 18V reverse standoff voltage and provides 29.2V maximum clamping voltage at peak pulse current of 13.7A, delivering 400W peak pulse power dissipation in a DO-214AC (SMA) package. The part is ROHS3 compliant with unlimited moisture sensitivity rating (MSL 1). Equivalent and substitute parts are identified to support procurement flexibility, inventory management, and design continuity across multiple manufacturers while maintaining electrical and mechanical compatibility.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	18	V
Voltage - Breakdown (Min)	20	V
Voltage - Clamping (Max) @ Ipp	29.2	V
Current - Peak Pulse (10/1000µs)	13.7	A
Power - Peak Pulse	400	W
Package / Case	DO-214AC, SMA	-
Mounting Type	Surface Mount	-
Operating Temperature Range	-55 to 175	°C
RoHS Status	ROHS3 Compliant	-

Substitute Part Grouping Explanation

Substitute parts for SMAJ18A-TP are classified into two categories based on electrical parameter alignment:

Direct Equivalents maintain identical electrical specifications across all critical parameters: 18V reverse standoff voltage, 20V minimum breakdown voltage, 29.2V maximum clamping voltage, 13.7A peak pulse current, and 400W peak pulse power. These parts are interchangeable at the circuit level and differ only in manufacturer, packaging format, or temperature rating variants. Direct equivalents include SMAJ18A (MDD), SMAJ18A-13-F (Diodes Incorporated), and SMAJ18A-E3/61 (Vishay General Semiconductor).

Similar Parts share the same 18V reverse standoff and 20V breakdown voltages but differ in clamping voltage and peak pulse current specifications. These parts include SM4T21AY (STMicroelectronics) with 39.3V clamping voltage and 59A peak pulse current, SMAJ18A-TR (STMicroelectronics) with 39.3V clamping and 59A current, and SMAJ18AE3/TR13 (Microchip Technology) with 29.2V clamping but 17.2A peak pulse current and 500W power rating.

Substitution eligibility is determined by matching the following critical parameters: Voltage - Reverse Standoff (18V), Voltage - Breakdown (20V minimum), Package / Case (DO-214AC, SMA), Mounting Type (Surface Mount), and RoHS Status (ROHS3 Compliant). Clamping voltage and peak pulse current variations indicate different protection characteristics and must be evaluated against circuit requirements.

Parameter Comparison

Part Number	Manufacturer	Voltage - Reverse Standoff (V)	Voltage - Breakdown (V)	Voltage - Clamping (V)	Current - Peak Pulse (A)	Power - Peak Pulse (W)	Operating Temperature (°C)	RoHS Status	Packaging
SMAJ18A-TP	Micro Commercial Co	18	20	29.2	13.7	400	-55 to 175	ROHS3	Tape & Reel (TR)
SMAJ18A	MDD	18	20	29.2	13.7	400	-50 to 150	ROHS3	-
SMAJ18A-13-F	Diodes Incorporated	18	20	29.2	13.7	400	-55 to 150	ROHS3	Tape & Reel (TR)
SMAJ18A-E3/61	Vishay General Semiconductor	18	20	29.2	13.7	400	-55 to 150	ROHS3	Cut Tape (CT)
SM4T21AY	STMicroelectronics	18	20	39.3	59 (8/20µs)	400	-55 to 150	ROHS3	Tape & Reel (TR)
SMAJ18A-TR	STMicroelectronics	18	20	39.3	59 (8/20µs)	400	-55 to 150	ROHS3	Cut Tape (CT) & Digi-Reel®
SMAJ18AE3/TR13	Microchip Technology	18	20	29.2	17.2	500	-65 to 150	ROHS3	Tape & Reel (TR)

Engineering Selection Recommendations

Direct Equivalent Selection: SMAJ18A-13-F (Diodes Incorporated) and SMAJ18A-E3/61 (Vishay General Semiconductor) are preferred direct equivalents. Both maintain identical electrical specifications (18V standoff, 29.2V clamping, 13.7A peak pulse current, 400W power) and are ROHS3 compliant. SMAJ18A-13-F supports the extended upper temperature range (-55°C to 150°C) matching the original part's lower bound. SMAJ18A-E3/61 is available in Cut Tape format for applications requiring individual component handling. The MDD variant SMAJ18A provides identical electrical performance but operates within a narrower temperature range (-50°C to 150°C), suitable for applications not requiring the -55°C lower temperature specification.

Similar Part Consideration: SM4T21AY and SMAJ18A-TR (both STMicroelectronics) provide higher peak pulse current (59A at 8/20µs pulse) and elevated clamping voltage (39.3V) while maintaining the 18V standoff voltage. These parts are suitable only for applications requiring enhanced transient suppression capability beyond the original 13.7A specification. SMAJ18AE3/TR13 (Microchip Technology) offers increased power dissipation (500W) and extended lower temperature range (-65°C) with slightly elevated peak pulse current (17.2A), appropriate for high-reliability or extreme-temperature environments.

All substitute parts maintain DO-214AC (SMA) package compatibility, surface-mount configuration, and ROHS3 compliance, ensuring PCB-level interchangeability without design modification.

Frequently Asked Questions (FAQ)

Q: Can SMAJ18A-TP be directly replaced with SMAJ18A-13-F? A: Yes. Both parts share identical electrical specifications: 18V reverse standoff voltage, 20V breakdown voltage, 29.2V clamping voltage, 13.7A peak pulse current, and 400W peak pulse power. Both are ROHS3 compliant and packaged in DO-214AC (SMA) surface-mount format. The primary difference is manufacturer (Diodes Incorporated vs. Micro Commercial Co) and packaging format (Tape & Reel).

Q: What is the difference between SMAJ18A-TP and SM4T21AY? A: Both parts maintain the same 18V reverse standoff and 20V breakdown voltages, but differ in transient suppression characteristics. SM4T21AY provides higher peak pulse current (59A at 8/20µs pulse specification) and elevated clamping voltage (39.3V) compared to SMAJ18A-TP (13.7A, 29.2V clamping). SM4T21AY is suitable for applications requiring enhanced overvoltage protection but will clamp at a higher voltage level.

Q: Are temperature rating differences significant when selecting a substitute? A: Temperature rating differences affect operational reliability in extreme environments. SMAJ18A-TP operates from -55°C to 175°C. Direct equivalents like SMAJ18A-13-F operate from -55°C to 150°C, providing adequate coverage for most industrial applications. SMAJ18AE3/TR13 extends the lower temperature limit to -65°C for cryogenic or aerospace applications. Verify circuit operating temperature requirements before substitution.

Q: Can SMAJ18A (MDD variant) replace SMAJ18A-TP? A: Electrical substitution is possible due to identical voltage and current specifications. However, the MDD variant operates within a narrower temperature range (-50°C to 150°C) compared to the original part (-55°C to 175°C). Substitution is acceptable only if the application does not require operation below -50°C or above 150°C.

Q: What packaging formats are available for SMAJ18A equivalents? A: Direct equivalents are available in Tape & Reel (TR) format for automated assembly and Cut Tape (CT) format for manual or semi-automated placement. SMAJ18A-13-F and SMAJ18A-TP are supplied in Tape & Reel. SMAJ18A-E3/61 is available in Cut Tape. Packaging selection depends on manufacturing process requirements and component handling procedures.

Q: Is SMAJ18AE3/TR13 a suitable substitute for general-purpose applications? A: SMAJ18AE3/TR13 maintains the same 18V standoff and 20V breakdown voltages as SMAJ18A-TP but offers enhanced specifications: 17.2A peak pulse current (vs. 13.7A), 500W power dissipation (vs. 400W), and extended lower temperature range (-65°C vs. -55°C). It is suitable as a substitute for general-purpose applications and provides additional design margin for transient protection. The higher current and power ratings do not negatively impact circuit performance.

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