MMBZ5256B Zener Diode 30V 350mW SOT-23-3 Equivalent & Substitute Parts

Part Overview

The MMBZ5256B is a 30V Zener diode rated for 350mW power dissipation in a surface mount SOT-23-3 package manufactured by onsemi. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The MMBZ5256B serves voltage regulation and protection applications requiring precise 30V Zener characteristics with ±5% tolerance in compact surface mount form factor.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	30	V
Tolerance	±5%	-
Power - Max	350	mW
Impedance (Max)	49	Ohms
Current - Reverse Leakage @ Vr	100	nA @ 23V
Voltage - Forward (Vf) (Max) @ If	900	mV @ 10mA
Operating Temperature	-55 to 150	°C
Mounting Type	Surface Mount	-
Package / Case	TO-236-3, SC-59, SOT-23-3	-

Substitute Part Grouping Explanation

Substitution of the MMBZ5256B is determined by the following critical parameters: Zener voltage (30V nominal), tolerance (±5%), power rating (350mW), impedance (49 Ohms maximum), reverse leakage current (100nA @ 23V), forward voltage (900mV @ 10mA), and package type (SOT-23-3). Substitute parts are grouped into three categories based on these specifications:

Direct Equivalents (Same Power Rating - 350mW): Parts maintaining the full 350mW power specification with identical electrical characteristics and SOT-23-3 packaging. These provide one-to-one replacement capability.

Reduced Power Alternatives (225mW Rating): onsemi parts with lower power dissipation (225mW) but identical voltage, tolerance, impedance, and leakage specifications. These are suitable for applications where the full 350mW capability is not required.

Cross-Manufacturer Alternatives: Parts from Diodes Incorporated, Micro Commercial Co, and Central Semiconductor Corp with 30V Zener voltage and SOT-23-3 packaging. These may have variations in impedance (80 Ohms), tolerance (±2% to ±7%), or power ratings (300mW to 500mW) and require circuit-level evaluation.

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Tolerance	Power (mW)	Zzt (Ohms)	Vf @ 10mA (mV)	Temp Range (°C)	Status
MMBZ5256B	onsemi	30	±5%	350	49	900	-55 to 150	Obsolete
MMBZ5256BLT1G	onsemi	30	±5%	225	49	900	-65 to 150	Active
MMBZ5256ELT1G	onsemi	30	±5%	225	49	900	-55 to 150	Active
SZMMBZ5256BLT1G	onsemi	30	±5%	225	49	900	-65 to 150	Active
SZMMBZ5256ELT1G	onsemi	30	±5%	225	49	900	-65 to 150	Active
MMBZ5256B-7-F	Diodes Incorporated	30	±5%	350	49	900	-65 to 150	Active
BZX84B30-TP	Micro Commercial Co	30	±2%	350	80	900	-55 to 150	Active
BZX84C30 BK	Central Semiconductor Corp	30	±5%	500	80	900	-65 to 150	Active
BZX84C30 TR TIN/LEAD	Central Semiconductor Corp	30	±5%	500	80	900	-65 to 150	Active
BZX84C30-7-F	Diodes Incorporated	30	±7%	300	80	900	-65 to 150	Active
BZX84C30-TP	Micro Commercial Co	30	±5%	350	80	80	-55 to 150	Active

Engineering Selection Recommendations

Primary Substitute - Direct Replacement (350mW Equivalent): MMBZ5256B-7-F (Diodes Incorporated) is the preferred direct substitute. It maintains identical electrical specifications (30V, ±5% tolerance, 350mW, 49 Ohms impedance) and SOT-23-3 packaging. This part is in active production status with extended operating temperature range (-65°C to 150°C) and RoHS3 compliance. Inventory availability is 3200 units.

Secondary Substitute - onsemi Active Alternatives (225mW): MMBZ5256BLT1G, MMBZ5256ELT1G, SZMMBZ5256BLT1G, and SZMMBZ5256ELT1G are active onsemi products with identical voltage, tolerance, impedance, and forward voltage characteristics. These parts are rated for 225mW instead of 350mW. Selection between these variants depends on temperature range requirements and automotive qualification needs. SZMMBZ5256BLT1G and SZMMBZ5256ELT1G include AEC-Q101 automotive qualification and extended temperature range (-65°C to 150°C). These substitutes are suitable for applications where power dissipation does not exceed 225mW.

Cross-Manufacturer Alternatives: BZX84C30-TP (Micro Commercial Co) and BZX84C30-7-F (Diodes Incorporated) provide 30V Zener voltage in SOT-23-3 packaging with active production status. These parts feature higher impedance (80 Ohms versus 49 Ohms) and require circuit-level evaluation. BZX84C30-TP offers 350mW power rating with ±5% tolerance. BZX84C30-7-F provides 300mW with ±7% tolerance. Central Semiconductor Corp BZX84C30 variants (BK and TR TIN/LEAD) offer 500mW power rating but are RoHS non-compliant.

Frequently Asked Questions (FAQ)

Q: Can MMBZ5256BLT1G replace MMBZ5256B in all applications? A: MMBZ5256BLT1G is electrically equivalent in voltage, tolerance, impedance, and leakage characteristics. However, it is rated for 225mW maximum power versus 350mW for the original part. Substitution is valid only if circuit power dissipation does not exceed 225mW. Verify thermal design margins before implementation.

Q: What is the difference between MMBZ5256BLT1G and SZMMBZ5256BLT1G? A: Both parts share identical electrical specifications (30V, ±5%, 225mW, 49 Ohms). SZMMBZ5256BLT1G includes AEC-Q101 automotive qualification and extended temperature range (-65°C to 150°C) versus standard -65°C to 150°C for MMBZ5256BLT1G. SZMMBZ5256BLT1G is specified for automotive applications.

Q: Why do cross-manufacturer parts show 80 Ohms impedance instead of 49 Ohms? A: Impedance (Zzt) is a characteristic of the specific diode design and manufacturing process. BZX84 series parts from Micro Commercial Co and Central Semiconductor Corp have higher impedance specifications. This affects voltage regulation performance under load changes. Verify impedance requirements for your specific application before substitution.

Q: Is MMBZ5256B-7-F a direct replacement for MMBZ5256B? A: Yes. MMBZ5256B-7-F from Diodes Incorporated maintains all critical specifications: 30V nominal voltage, ±5% tolerance, 350mW power rating, 49 Ohms impedance, and SOT-23-3 packaging. It is in active production with RoHS3 compliance and extended temperature range (-65°C to 150°C).

Q: Can I use BZX84C30 variants with 500mW rating as a substitute? A: BZX84C30 BK and BZX84C30 TR TIN/LEAD from Central Semiconductor Corp provide 30V Zener voltage with higher power rating (500mW) and are electrically compatible. However, these parts are RoHS non-compliant. Additionally, impedance is 80 Ohms versus 49 Ohms. Use only if RoHS compliance is not required and circuit design accommodates higher impedance.

Q: What packaging options are available for 30V Zener diode substitutes? A: All listed substitutes use SOT-23-3 (TO-236-3, SC-59) surface mount packaging, matching the original MMBZ5256B. Packaging variants include Tape & Reel (TR), Cut Tape (CT), and Bulk options. Verify supplier device package designation when ordering to ensure correct tape format and reel specifications.

Q: Are automotive-grade alternatives available? A: Yes. SZMMBZ5256BLT1G and SZMMBZ5256ELT1G are AEC-Q101 qualified automotive-grade parts from onsemi with 225mW power rating. These parts meet automotive reliability standards and extended temperature specifications (-65°C to 150°C).

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