MMBZ5251B Equivalent & Substitute Parts

Part Overview

The MMBZ5251B is a 22 V Zener diode rated for 350 mW maximum power dissipation in a surface mount SOT-23-3 package. Manufactured by onsemi, this component is classified as obsolete. Due to its obsolete status, direct equivalents and active substitutes are necessary for new designs and production continuity. Substitute parts maintain the core electrical specifications while offering active product status and improved availability from alternative manufacturers.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nominal)	22	V
Tolerance	±5%	—
Power - Maximum	350	mW
Impedance (Maximum)	29	Ohms
Current - Reverse Leakage @ Vr	100 nA @ 17 V	—
Voltage - Forward (Maximum) @ If	900 mV @ 10 mA	—
Operating Temperature Range	-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 MMBZ5251B is determined by the following critical parameters:

Primary Matching Criteria:

Voltage - Zener (Nominal): 22 V
Package / Case: SOT-23-3 (TO-236-3, SC-59)
Mounting Type: Surface Mount
Power - Maximum: 350 mW (or higher)
Operating Temperature Range: Must encompass or exceed -55°C to 150°C

Secondary Compatibility Factors:

Tolerance: ±5% or tighter
Impedance (Maximum): 29 Ohms or lower preferred; up to 55 Ohms acceptable with design verification
Current - Reverse Leakage: 100 nA @ 17 V or lower
Voltage - Forward (Maximum): 900 mV @ 10 mA

Substitute parts are grouped into two categories:

Category A - Direct Electrical Equivalents: Parts matching all primary criteria with identical or superior electrical performance (MMBZ5251B-7-F, CMPZ5251B TR PBFREE, MMBZ5251BLT1G).

Category B - Functional Equivalents: Parts meeting primary criteria with minor parameter variations in impedance, tolerance, or temperature range that remain within acceptable design margins (BZX84C22 TR, BZX84C22-7-F, BZX84C22-TP, BZX84B22-TP, CZRT5251B-G, CZRT55C22-G, MMBZ5251B-TP).

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Tolerance	Power (mW)	Zzt (Ohms)	Ir @ Vr	Vf (Max) @ If	Temp Range (°C)	Package	Status
MMBZ5251B	onsemi	22	±5%	350	29	100 nA @ 17 V	900 mV @ 10 mA	-55 to 150	SOT-23-3	Obsolete
MMBZ5251B-7-F	Diodes Incorporated	22	±5%	350	29	100 nA @ 17 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
MMBZ5251BLT1G	onsemi	22	±5%	225	29	100 nA @ 17 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
CMPZ5251B TR PBFREE	Central Semiconductor Corp	22	±5%	350	29	100 nA @ 17 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
BZX84C22 TR	Central Semiconductor Corp	22	±5%	350	55	50 nA @ 15.4 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
BZX84C22-7-F	Diodes Incorporated	22	±6%	300	55	100 nA @ 15.4 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
BZX84C22-TP	Micro Commercial Co	22	±5%	350	55	100 nA @ 15.4 V	900 mV @ 10 mA	-55 to 150	SOT-23-3	Active
BZX84B22-TP	Micro Commercial Co	22	±2%	350	55	100 nA @ 15.4 V	900 mV @ 10 mA	-55 to 150	SOT-23-3	Active
CZRT5251B-G	Comchip Technology	22	±5%	300	29	100 nA @ 17 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
CZRT55C22-G	Comchip Technology	22	±6%	350	55	100 nA @ 15.4 V	900 mV @ 10 mA	-65 to 150	SOT-23-3	Active
MMBZ5251B-TP	Micro Commercial Co	22	±5%	350	29	100 nA @ 17 V	900 mV @ 10 mA	-55 to 150	SOT-23-3	Active

Engineering Selection Recommendations

Tier 1 - Preferred Substitutes (Direct Equivalents):

MMBZ5251B-7-F (Diodes Incorporated) and CMPZ5251B TR PBFREE (Central Semiconductor Corp) are the primary recommended substitutes. Both maintain identical electrical specifications to the original MMBZ5251B, including 22 V nominal voltage, ±5% tolerance, 350 mW power rating, and 29 Ohms maximum impedance. Both are active products with RoHS3 compliance and extended operating temperature ranges (-65°C to 150°C). These parts provide direct functional replacement with no design modifications required.

Tier 2 - Functional Equivalents (Acceptable Substitutes):

BZX84C22 TR (Central Semiconductor Corp), BZX84C22-TP (Micro Commercial Co), and CZRT55C22-G (Comchip Technology) meet all primary electrical criteria with 22 V nominal voltage and 350 mW power rating. These parts feature higher impedance (55 Ohms versus 29 Ohms) and slightly different tolerance specifications (±5% to ±6%). All are active products with RoHS3 compliance and suitable for applications where the impedance variation is acceptable.

Tier 3 - Reduced Power Alternatives:

MMBZ5251BLT1G (onsemi) and CZRT5251B-G (Comchip Technology) provide 225 mW and 300 mW power ratings respectively, compared to the original 350 mW specification. These parts are suitable only for applications where power dissipation requirements are lower than the original design specification. Both maintain 22 V nominal voltage, ±5% tolerance, and 29 Ohms impedance.

Tier 4 - Tighter Tolerance Alternative:

BZX84B22-TP (Micro Commercial Co) offers ±2% tolerance compared to the original ±5%, providing improved voltage accuracy. This part is suitable for precision applications requiring tighter voltage regulation. It maintains 350 mW power rating and SOT-23-3 packaging.

All recommended substitutes are surface mount components in SOT-23-3 packages with identical mechanical compatibility to the original MMBZ5251B.

Frequently Asked Questions (FAQ)

Q: Can MMBZ5251BLT1G be used as a direct replacement for MMBZ5251B?

A: MMBZ5251BLT1G is electrically compatible with identical voltage and tolerance specifications. However, it is rated for 225 mW maximum power versus the original 350 mW. Use this substitute only if your circuit design requires less than 225 mW power dissipation. For applications requiring the full 350 mW rating, select MMBZ5251B-7-F or CMPZ5251B TR PBFREE instead.

Q: What is the difference between parts with 29 Ohms and 55 Ohms impedance?

A: Impedance affects the dynamic resistance of the Zener diode during transient conditions. The 29 Ohms specification (MMBZ5251B, MMBZ5251B-7-F, CMPZ5251B TR PBFREE, CZRT5251B-G, MMBZ5251B-TP) provides lower impedance and faster transient response. The 55 Ohms specification (BZX84C22 TR, BZX84C22-7-F, BZX84C22-TP, BZX84B22-TP, CZRT55C22-G) is acceptable for most applications but may exhibit slightly slower voltage regulation during rapid load changes. Select based on your circuit's transient performance requirements.

Q: Are all substitute parts RoHS3 compliant?

A: All listed substitute parts are RoHS3 compliant and REACH unaffected. The original MMBZ5251B does not specify RoHS status due to its obsolete classification. All active substitutes meet current environmental compliance standards.

Q: Can I use BZX84C22-7-F if my design requires 350 mW?

A: BZX84C22-7-F is rated for 300 mW maximum power, which is 50 mW below the original 350 mW specification. Use this part only if your circuit design dissipates 300 mW or less. For applications requiring the full 350 mW rating, select BZX84C22 TR, BZX84C22-TP, BZX84B22-TP, or CZRT55C22-G instead.

Q: What is the temperature range difference between -55°C and -65°C?

A: The original MMBZ5251B operates from -55°C to 150°C. Several substitutes extend the lower temperature limit to -65°C (MMBZ5251B-7-F, CMPZ5251B TR PBFREE, BZX84C22 TR, BZX84C22-7-F, CZRT5251B-G, CZRT55C22-G). This extended range provides additional margin for applications in cold environments. Parts rated only to -55°C (BZX84C22-TP, BZX84B22-TP, MMBZ5251B-TP) are suitable for standard industrial temperature ranges.

Q: Are all substitutes available in the same packaging?

A: All listed substitutes use SOT-23-3 (TO-236-3, SC-59) surface mount packaging, identical to the original MMBZ5251B. Packaging variations exist only in tape format (Tape & Reel, Cut Tape, or Bulk), which affects handling and assembly but not component compatibility. Verify your procurement requirements for the appropriate packaging format.

Q: Which substitute offers the best voltage accuracy?

A: BZX84B22-TP provides ±2% tolerance, the tightest specification among all listed substitutes. The original MMBZ5251B and most substitutes specify ±5% tolerance. BZX84C22-7-F and CZRT55C22-G specify ±6% tolerance. Select BZX84B22-TP for precision voltage regulation applications requiring tighter tolerance control.

Q: Can I mix different substitute parts in the same production run?

A: All listed substitutes maintain the same 22 V nominal voltage and SOT-23-3 package, allowing interchangeability at the board level. However, mixing parts with different impedance values (29 Ohms versus 55 Ohms) or power ratings (225 mW, 300 mW, or 350 mW) may result in inconsistent circuit performance. For production consistency, select a single substitute part number and maintain it throughout the manufacturing process.

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