SMAJ24 Transient Voltage Suppressor (TVS) Diode - Equivalent & Substitute Parts

Part Overview

The SMAJ24 is a unidirectional Zener-type transient voltage suppressor manufactured by Littelfuse, designed for general-purpose overvoltage protection in surface-mount applications. The device features a 24V reverse standoff voltage with a 40.85V maximum clamping voltage at peak pulse current. Currently classified as obsolete, the SMAJ24 requires identification of active equivalent and substitute parts to maintain design continuity and ensure supply chain availability for new production and field replacements.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	24	V
Voltage - Breakdown (Min)	25.29	V
Voltage - Clamping (Max) @ Ipp	40.85	V
Current - Peak Pulse (10/1000µs)	10.3	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	—
Unidirectional Channels	1	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the SMAJ24 is determined by strict alignment of the following electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - Reverse Standoff: 24V (exact match required)
Voltage - Breakdown (Min): 25.29V to 26.7V (acceptable range)
Package / Case: DO-214AC, SMA (mechanical compatibility)
Mounting Type: Surface Mount (assembly compatibility)
Type: Zener, Unidirectional (functional equivalence)
RoHS Status: ROHS3 Compliant (regulatory requirement)

Secondary Consideration:

Voltage - Clamping (Max) @ Ipp: Acceptable range 38.9V to 50V (within circuit protection tolerance)
Current - Peak Pulse: Acceptable range 10.28A to 80A (higher ratings provide margin)
Power - Peak Pulse: Acceptable range 400W to 4000W (higher ratings provide margin)
Operating Temperature: Minimum -55°C to -65°C and maximum 150°C to 175°C (acceptable overlap)

Substitute parts meeting these criteria maintain functional equivalence for general-purpose transient voltage suppression applications while ensuring mechanical and electrical compatibility with the original SMAJ24 design.

Parameter Comparison

Part Number	Manufacturer	Status	Standoff (V)	Breakdown Min (V)	Clamp Max @ Ipp (V)	Peak Pulse (A)	Power (W)	Temp Range (°C)	Package
SMAJ24	Littelfuse	Obsolete	24	25.29	40.85	10.3	400	-65 to 150	DO-214AC, SMA
SMAJ24A	MDD	Active	24	26.7	38.9	10.3	400	-50 to 150	DO-214AC, SMA
SZ1SMA24AT3G	Littelfuse Inc.	Active	24	26.7	38.9	10.3	400	-65 to 150	DO-214AC, SMA
SMA6J24A-E3/5A	Vishay General Semiconductor	Active	24	26.7	44.3	80 (8/20µs)	4000	-55 to 150	DO-214AC, SMA
SMA6J24A-TP	Micro Commercial Co	Active	24	26.7	38.9	15.4	600	-55 to 175	DO-214AC, SMA
SMAJ24A-13-F	Diodes Incorporated	Active	24	26.7	38.9	10.3	400	-55 to 150	DO-214AC, SMA
SMAJ24A-TR	STMicroelectronics	Active	24	26.7	50	46 (8/20µs)	400	-55 to 150	DO-214AC, SMA
SMAJ24AE3/TR13	Microchip Technology	Active	24	26.7	38.9	12.8	500	-65 to 150	DO-214AC, SMA
SMAJ24E3/TR13	Microchip Technology	Active	24	26.7	43	11.6	500	-65 to 150	DO-214AC, SMA
TV04A240J-G	Comchip Technology	Active	24	26.7	38.9	10.28	400	-55 to 150	DO-214AC, SMA

Engineering Selection Recommendations

All listed substitute parts maintain active product status and ROHS3 compliance, ensuring regulatory alignment and supply chain continuity. Selection among equivalent parts should be based on the following factors:

Direct Electrical Equivalents (Recommended Primary Choices):

SZ1SMA24AT3G (Littelfuse Inc.) maintains the original manufacturer lineage with identical electrical specifications and extended temperature range (-65°C to 150°C), providing the closest functional replacement.
SMAJ24A-13-F (Diodes Incorporated) and TV04A240J-G (Comchip Technology) provide equivalent clamping voltage (38.9V) and peak pulse current (10.3A to 10.28A) with active status.

Higher Performance Alternatives:

SMA6J24A-E3/5A (Vishay) and SMAJ24A-TR (STMicroelectronics) offer elevated peak pulse current ratings (80A and 46A respectively) and higher clamping voltages (44.3V and 50V), suitable for applications requiring enhanced transient suppression margin.
SMA6J24A-TP (Micro Commercial Co) provides intermediate performance with 15.4A peak pulse current and extended upper temperature rating (175°C).

Microchip Technology Options:

SMAJ24AE3/TR13 and SMAJ24E3/TR13 offer clamping voltages of 38.9V and 43V respectively with peak pulse currents of 12.8A and 11.6A, maintaining the full temperature range (-65°C to 150°C).

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

Frequently Asked Questions (FAQ)

Q: Can SMAJ24A directly replace the obsolete SMAJ24? A: Yes. SMAJ24A (MDD) maintains the 24V reverse standoff voltage, 10.3A peak pulse current, and 400W power rating. The clamping voltage is 38.9V compared to the original 40.85V, which remains within acceptable circuit protection tolerance for general-purpose applications. Both use DO-214AC (SMA) packaging.

Q: What is the difference between the various Microchip Technology options (SMAJ24AE3/TR13 and SMAJ24E3/TR13)? A: Both are Microchip products with identical 24V standoff voltage and -65°C to 150°C operating range. SMAJ24AE3/TR13 has a clamping voltage of 38.9V with 12.8A peak pulse current, while SMAJ24E3/TR13 has a clamping voltage of 43V with 11.6A peak pulse current. Selection depends on the specific circuit protection requirement.

Q: Why do some substitute parts have higher peak pulse current ratings (80A, 46A)? A: Higher peak pulse current ratings (SMA6J24A-E3/5A at 80A and SMAJ24A-TR at 46A) provide additional transient suppression capability and design margin. These parts maintain the 24V standoff voltage and DO-214AC (SMA) package, making them suitable for applications requiring enhanced protection without redesign.

Q: Are all substitute parts RoHS3 compliant? A: Yes. All listed substitute parts are ROHS3 compliant with MSL rating of 1 (Unlimited), meeting current regulatory requirements and ensuring compatibility with modern manufacturing processes.

Q: Does package compatibility affect substitution? A: No. All substitute parts use the DO-214AC (SMA) surface-mount package, ensuring direct mechanical compatibility with existing PCB layouts, solder pads, and assembly equipment. No board redesign is required.

Q: What is the significance of the Littelfuse SZ1SMA24AT3G designation? A: SZ1SMA24AT3G is the Littelfuse successor to the SMAJ24 series. It maintains the original manufacturer's design with identical electrical specifications (24V standoff, 38.9V clamp, 10.3A peak pulse) and the full operating temperature range (-65°C to 150°C), providing the most direct replacement path.

Q: Can I use a substitute with a higher clamping voltage (50V vs. 40.85V)? A: Yes, within circuit design constraints. SMAJ24A-TR (STMicroelectronics) has a 50V clamping voltage compared to the original 40.85V. The higher clamping voltage provides additional protection margin but may affect circuit behavior if the original design relied on the specific 40.85V threshold. Circuit validation is necessary for critical applications.

Q: What is the difference between cut tape (CT) and tape & reel (TR) packaging? A: Cut tape and tape & reel are distribution formats, not component differences. Tape & reel is used for automated assembly lines, while cut tape is used for manual or lower-volume assembly. The electrical and mechanical specifications remain identical; selection depends on manufacturing process requirements.

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