MMSZ51T1 Equivalent & Substitute Parts

Part Overview

The MMSZ51T1 is a 51 V, 500 mW Zener diode manufactured by onsemi in SOD-123 surface mount packaging. This component is classified as obsolete, which necessitates identification of equivalent and substitute parts for ongoing design requirements and procurement needs. The part operates across a temperature range of -55°C to 150°C with ±5% voltage tolerance and is RoHS non-compliant.

Equivalent parts maintain identical electrical and mechanical specifications, while substitute parts provide functional alternatives with acceptable parameter variations within engineering tolerances for 51 V Zener diode applications.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	51	V
Power - Max	500	mW
Tolerance	±5%	—
Impedance (Max)	180	Ohms
Current - Reverse Leakage @ Vr	50	nA @ 35.7 V
Voltage - Forward (Max) @ If	900	mV @ 10 mA
Operating Temperature	-55 to 150	°C
Package / Case	SOD-123	—
Mounting Type	Surface Mount	—

Substitute Part Grouping Explanation

Substitution of the MMSZ51T1 is determined by the following critical parameters:

Primary Matching Criteria:

Zener voltage: 51 V nominal
Package type: SOD-123 surface mount
Operating temperature range: -55°C to 150°C minimum
Mounting type: Surface mount

Secondary Compatibility Factors:

Power dissipation rating (500 mW or higher acceptable)
Voltage tolerance (±5% or tighter acceptable)
Impedance characteristics (180 Ohms or lower acceptable)
Reverse leakage current specifications

Parts are grouped into two categories:

Direct Equivalent: MMSZ51T1G (onsemi) — Identical electrical specifications with active product status and RoHS3 compliance. Differs only in packaging format (Tape & Reel) and compliance certifications.

Functional Substitutes: BZT52 series parts (Vishay) and BZT52C51S-7 (Diodes Incorporated) — Maintain 51 V nominal Zener voltage and SOD-123 packaging with acceptable parameter variations. BZT52 series exhibits lower maximum power dissipation (410 mW vs. 500 mW) and lower impedance (100 Ohms vs. 180 Ohms), with tighter voltage tolerance options (±2% available). BZT52C51S-7 uses SOD-323 package variant with 200 mW power rating and ±6% tolerance.

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Power (mW)	Tolerance	Zzt (Ohms)	Package	Status	RoHS
MMSZ51T1	onsemi	51	500	±5%	180	SOD-123	Obsolete	Non-compliant
MMSZ51T1G	onsemi	51	500	±5%	180	SOD-123	Active	RoHS3
BZT52B51-E3-08	Vishay	51	410	±2%	100	SOD-123	Active	RoHS3
BZT52B51-E3-18	Vishay	51	410	±2%	100	SOD-123	Active	RoHS3
BZT52B51-G3-08	Vishay	51	410	±2%	100	SOD-123	Active	RoHS3
BZT52B51-G3-18	Vishay	51	410	±2%	100	SOD-123	Active	RoHS3
BZT52C51-E3-08	Vishay	51	410	±5%	100	SOD-123	Active	RoHS3
BZT52C51-E3-18	Vishay	51	410	±5%	100	SOD-123	Active	RoHS3
BZT52C51-G3-08	Vishay	51	410	±5%	100	SOD-123	Active	RoHS3
BZT52C51-G3-18	Vishay	51	410	±5%	100	SOD-123	Active	RoHS3
BZT52C51S-7	Diodes Inc.	51	200	±6%	100	SOD-323	Active	RoHS3

Engineering Selection Recommendations

Primary Selection: MMSZ51T1G

The MMSZ51T1G is the direct equivalent replacement for the obsolete MMSZ51T1. This part maintains identical electrical specifications (51 V, 500 mW, ±5% tolerance, 180 Ohms impedance) and identical SOD-123 packaging. The primary advantages are active product status, RoHS3 compliance, and significantly higher inventory availability (9,404 units in stock versus 733 units for the original part). This part is suitable for direct substitution in all applications where the MMSZ51T1 was originally specified.

Secondary Selection: BZT52 Series (Vishay)

The BZT52 series from Vishay provides functional substitutes across multiple variants. All BZT52 51 V Zener diodes maintain the critical 51 V nominal voltage and SOD-123 package format. These parts are active, RoHS3 compliant, and available in high quantities. The trade-off is reduced maximum power dissipation (410 mW versus 500 mW) and lower impedance (100 Ohms versus 180 Ohms).

Selection within the BZT52 series depends on tolerance and packaging requirements:

BZT52B51 variants (±2% tolerance) provide tighter voltage regulation for precision applications
BZT52C51 variants (±5% tolerance) match the original MMSZ51T1 tolerance specification
E3-08 and E3-18 suffixes indicate different tape reel configurations; selection depends on procurement and assembly requirements

Tertiary Selection: BZT52C51S-7

The BZT52C51S-7 from Diodes Incorporated is suitable only for applications where reduced power dissipation (200 mW) is acceptable. This part uses SOD-323 packaging, which differs from the SOD-123 footprint of the original part and requires PCB layout modification. This part is appropriate for low-power applications where the smaller package size provides design advantages.

Frequently Asked Questions (FAQ)

Q: Can MMSZ51T1G be used as a direct replacement for MMSZ51T1?

A: Yes. MMSZ51T1G is the direct equivalent with identical electrical specifications and SOD-123 packaging. The only differences are active product status, RoHS3 compliance, and packaging format (Tape & Reel). No circuit modifications are required.

Q: What is the key difference between BZT52B51 and BZT52C51 variants?

A: The primary difference is voltage tolerance. BZT52B51 variants specify ±2% tolerance, while BZT52C51 variants specify ±5% tolerance, matching the original MMSZ51T1. Both maintain 51 V nominal voltage and 410 mW power dissipation. Selection depends on circuit tolerance requirements.

Q: Can BZT52 series parts replace MMSZ51T1 in all applications?

A: BZT52 series parts are suitable substitutes for most applications. However, the reduced power dissipation (410 mW versus 500 mW) and lower impedance (100 Ohms versus 180 Ohms) must be evaluated against circuit requirements. Applications requiring the full 500 mW power rating should use MMSZ51T1G instead.

Q: What does the E3-08 and E3-18 suffix indicate on BZT52 parts?

A: These suffixes indicate tape reel packaging configurations. E3-08 and E3-18 refer to different reel specifications for automated assembly. Both provide identical electrical performance; selection depends on procurement and assembly equipment compatibility.

Q: Is BZT52C51S-7 compatible with the original MMSZ51T1 PCB footprint?

A: No. BZT52C51S-7 uses SOD-323 packaging, while MMSZ51T1 uses SOD-123 packaging. These packages have different footprints and pin configurations. PCB layout modification is required for this substitution. This part is suitable only for new designs or redesigns where the smaller package provides advantages.

Q: Why is the MMSZ51T1 marked as obsolete?

A: The MMSZ51T1 is obsolete, but the equivalent MMSZ51T1G remains in active production. The MMSZ51T1G provides identical functionality with improved compliance status and availability. Procurement should transition to MMSZ51T1G for new designs and ongoing production.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All listed substitute parts (MMSZ51T1G, BZT52 series, and BZT52C51S-7) are RoHS3 compliant. The original MMSZ51T1 is RoHS non-compliant. This compliance improvement is a significant advantage for applications subject to RoHS regulations.

Q: What is the impact of lower impedance in BZT52 substitutes?

A: Lower impedance (100 Ohms versus 180 Ohms) results in better voltage regulation and lower dynamic resistance. This is generally beneficial for circuit performance, providing improved stability and reduced voltage variation under load changes. No negative impact is expected in standard applications.

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