SMAJ51 Transient Voltage Suppressor (TVS) Diode - Equivalent & Substitute Parts

Part Overview

The SMAJ51 is a unidirectional Zener-type transient voltage suppressor manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. The device features a 51V reverse standoff voltage with an 86.52V maximum clamping voltage at peak pulse current and is packaged in the DO-214AC (SMA) form factor. The SMAJ51 is currently listed as obsolete, making identification of active equivalent parts essential for ongoing design support and procurement.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	51	V
Voltage - Breakdown (Min)	53.73	V
Voltage - Clamping (Max) @ Ipp	86.52	V
Current - Peak Pulse (10/1000µs)	4.9	A
Power - Peak Pulse	400	W
Package / Case	DO-214AC, SMA	—
Operating Temperature Range	-65°C ~ 150°C	TJ
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the SMAJ51 is determined by strict alignment of the following electrical and mechanical parameters:

Reverse Standoff Voltage (Typ): Must equal 51V
Package / Case: Must be DO-214AC (SMA) surface mount
Type: Must be Zener unidirectional TVS diode
Unidirectional Channels: Must be 1
Applications: General Purpose
RoHS Compliance: ROHS3 Compliant

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

Category A (Lower Clamping Voltage): Parts with maximum clamping voltage of 82.4V at peak pulse current. These include SMAJ51A (MDD), SMAJ51A-13-F (Diodes Incorporated), SMAJ51A-TP (Micro Commercial Co), and TV04A510J-G (Comchip Technology). All maintain 4.85A to 4.9A peak pulse current and 400W peak pulse power.

Category B (Higher Clamping Voltage): Parts with maximum clamping voltage exceeding 82.4V. SMAJ51AE3/TR13 (Microchip Technology) provides 82.4V clamping with 6.1A peak pulse current and 500W peak pulse power. SMAJ51E3/TR13 (Microchip Technology) provides 91.1V clamping with 5.5A peak pulse current and 500W peak pulse power.

Parameter Comparison

Part Number	Manufacturer	Voltage - Reverse Standoff (Typ)	Voltage - Breakdown (Min)	Voltage - Clamping (Max) @ Ipp	Current - Peak Pulse (10/1000µs)	Power - Peak Pulse	Operating Temperature	Product Status
SMAJ51	Littelfuse Inc.	51V	53.73V	86.52V	4.9A	400W	-65°C ~ 150°C (TJ)	Obsolete
SMAJ51A	MDD	51V	56.7V	82.4V	4.9A	400W	-50°C ~ 150°C (TJ)	Active
SMAJ51A-13-F	Diodes Incorporated	51V	56.7V	82.4V	4.9A	400W	-55°C ~ 150°C (TJ)	Active
SMAJ51A-TP	Micro Commercial Co	51V	56.7V	82.4V	4.9A	400W	-55°C ~ 175°C (TA)	Active
SMAJ51AE3/TR13	Microchip Technology	51V	56.7V	82.4V	6.1A	500W	-65°C ~ 150°C (TJ)	Active
SMAJ51E3/TR13	Microchip Technology	51V	56.7V	91.1V	5.5A	500W	-65°C ~ 150°C (TJ)	Active
TV04A510J-G	Comchip Technology	51V	56.7V	82.4V	4.85A	400W	-55°C ~ 150°C (TJ)	Active

Engineering Selection Recommendations

All substitute parts listed maintain ROHS3 compliance and MSL 1 (Unlimited) moisture sensitivity rating, ensuring compatibility with standard manufacturing and storage protocols.

For direct electrical replacement with minimal design impact: SMAJ51A-13-F (Diodes Incorporated) and SMAJ51A-TP (Micro Commercial Co) are recommended. Both are active products with high inventory availability (41,300 and 35,400 units respectively), matching the original 51V standoff voltage, 82.4V clamping voltage, 4.9A peak pulse current, and 400W peak pulse power. SMAJ51A-13-F operates across -55°C to 150°C, while SMAJ51A-TP extends to -55°C to 175°C.

For enhanced performance with higher current handling: SMAJ51AE3/TR13 (Microchip Technology) provides 6.1A peak pulse current and 500W peak pulse power while maintaining 82.4V clamping voltage and the full -65°C to 150°C temperature range of the original part.

For applications requiring higher clamping voltage: SMAJ51E3/TR13 (Microchip Technology) delivers 91.1V maximum clamping voltage with 5.5A peak pulse current and 500W peak pulse power, suitable for circuits where higher transient suppression voltage is acceptable.

For cost-optimized procurement: SMAJ51A (MDD) offers active product status with 1,648 units in stock, though operating temperature is limited to -50°C to 150°C.

Frequently Asked Questions (FAQ)

Q: Can SMAJ51A-13-F directly replace SMAJ51 without circuit modification?

A: Yes. SMAJ51A-13-F maintains the same 51V reverse standoff voltage, 82.4V clamping voltage, 4.9A peak pulse current, and DO-214AC (SMA) package. The lower clamping voltage (82.4V vs. 86.52V) provides slightly tighter transient suppression. Verify circuit tolerance for this 3.72V reduction in maximum clamping voltage.

Q: What is the difference between SMAJ51AE3/TR13 and SMAJ51E3/TR13?

A: Both are Microchip Technology products with identical 51V standoff voltage and DO-214AC (SMA) packaging. SMAJ51AE3/TR13 provides 82.4V clamping with 6.1A peak pulse current. SMAJ51E3/TR13 provides 91.1V clamping with 5.5A peak pulse current. Selection depends on whether higher current handling or higher clamping voltage is required.

Q: Are all substitute parts available in Tape & Reel (TR) packaging?

A: Yes. All listed substitute parts are supplied in Tape & Reel (TR) packaging, consistent with surface-mount manufacturing requirements.

Q: Does the operating temperature range difference affect substitution?

A: Operating temperature ranges vary among substitutes. SMAJ51A is limited to -50°C to 150°C, while SMAJ51AE3/TR13 and SMAJ51E3/TR13 extend to -65°C to 150°C, matching the original SMAJ51. For applications requiring the full -65°C lower temperature limit, select Microchip Technology variants or SMAJ51A-13-F (-55°C minimum).

Q: Is the SMAJ51 truly obsolete?

A: Yes. The SMAJ51 is listed as obsolete. All recommended substitutes are active products with current manufacturing and inventory support.

Q: Can TV04A510J-G be used as a direct replacement?

A: Yes. TV04A510J-G (Comchip Technology) matches the 51V standoff voltage, 82.4V clamping voltage, and 4.9A peak pulse current. Peak pulse power is 400W. Operating temperature range is -55°C to 150°C. Verify compatibility with your circuit's lower temperature requirement if operation below -55°C is needed.

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