MMBZ5248B Zener Diode Equivalent & Substitute Parts

Part Overview

The MMBZ5248B is an 18 V, 350 mW surface mount zener diode manufactured by onsemi in SOT-23-3 package configuration. This component is classified as obsolete, indicating discontinuation from the original manufacturer. Equivalent and substitute parts are necessary to maintain design continuity, ensure supply chain availability, and support ongoing production requirements for applications utilizing this zener diode specification.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	18	V
Tolerance	±5%	—
Power - Max	350	mW
Impedance (Max)	21	Ohms
Current - Reverse Leakage @ Vr	100	nA @ 14 V
Voltage - Forward (Vf) (Max) @ If	900	mV @ 10 mA
Operating Temperature	-55°C ~ 150°C	—
Mounting Type	Surface Mount	—
Package / Case	TO-236-3, SC-59, SOT-23-3	—

Substitute Part Grouping Explanation

Substitution of the MMBZ5248B is determined by the following critical parameters:

Primary Substitution Criteria:

Voltage - Zener (Nom): 18 V (exact match required)
Tolerance: ±5% or tighter (±2%, ±5%, ±6% acceptable)
Power - Max: 350 mW or greater (225 mW variants are lower-rated alternatives)
Impedance (Max): 21 Ohms or 45 Ohms (both acceptable within zener diode specifications)
Current - Reverse Leakage @ Vr: 50 nA to 100 nA (acceptable range)
Voltage - Forward (Vf) (Max) @ If: 900 mV @ 10 mA (exact match)
Operating Temperature: -55°C to -65°C minimum, 150°C maximum
Mounting Type: Surface Mount (required)
Package / Case: SOT-23-3 or TO-236-3 (physically compatible)

Substitute parts are categorized into two groups:

Group 1: Direct Equivalents (350 mW Power Rating) Parts maintaining the original 350 mW power specification with identical or superior electrical characteristics.

Group 2: Functional Alternatives (225 mW Power Rating) Parts with reduced power dissipation capability but matching zener voltage and tolerance specifications. These are suitable for applications with lower power requirements.

Parameter Comparison

Part Number	Manufacturer	Vz (V)	Tolerance	Power (mW)	Zzt (Ohms)	Vf @ 10mA (mV)	Temp Range (°C)	Status
MMBZ5248B	onsemi	18	±5%	350	21	900	-55 ~ 150	Obsolete
MMBZ5248B-7-F	Diodes Incorporated	18	±5%	350	21	900	-65 ~ 150	Active
BZX84C18 TR PBFREE	Central Semiconductor Corp	18	±5%	350	45	900	-65 ~ 150	Active
BZX84C18-TP	Micro Commercial Co	18	±5%	350	45	900	-55 ~ 150	Active
BZX84B18-TP	Micro Commercial Co	18	±2%	350	45	900	-55 ~ 150	Active
CMPZ5248B TR PBFREE	Central Semiconductor Corp	18	±5%	350	21	900	-65 ~ 150	Active
CZRT55C18-G	Comchip Technology	18	±6%	350	45	900	-65 ~ 150	Active
MMBZ5248BLT1G	onsemi	18	±5%	225	21	900	-65 ~ 150	Active
MMBZ5248BLT3G	onsemi	18	±5%	225	21	900	-65 ~ 150	Active
MMBZ5248ELT1G	onsemi	18	±5%	225	21	900	-55 ~ 150	Active
SZMMBZ5248BLT1G	onsemi	18	±5%	225	21	900	-65 ~ 150	Active

Engineering Selection Recommendations

For Direct Replacement (350 mW Equivalent Power Rating):

The MMBZ5248B-7-F (Diodes Incorporated) provides the most direct equivalent specification, maintaining 350 mW power dissipation, 21 Ohms impedance, and extending the operating temperature range to -65°C. This part is active and RoHS3 compliant.

The CMPZ5248B TR PBFREE (Central Semiconductor Corp) offers identical electrical specifications with 350 mW power rating and 21 Ohms impedance, with extended temperature range to -65°C and active product status.

The BZX84C18 TR PBFREE (Central Semiconductor Corp) and BZX84C18-TP (Micro Commercial Co) maintain 350 mW power rating with 45 Ohms impedance and active status. These parts are suitable where impedance tolerance of 45 Ohms is acceptable.

The BZX84B18-TP (Micro Commercial Co) provides tighter tolerance specification (±2%) with 350 mW power rating and active status, suitable for applications requiring improved voltage accuracy.

For Reduced Power Applications (225 mW Alternative Rating):

The MMBZ5248BLT1G, MMBZ5248BLT3G, MMBZ5248ELT1G, and SZMMBZ5248BLT1G (all onsemi) are active alternatives with 225 mW power rating. These parts maintain 18 V zener voltage, ±5% tolerance, and 21 Ohms impedance. The SZMMBZ5248BLT1G includes AEC-Q101 automotive qualification. These variants are suitable for applications where power dissipation requirements are lower than the original 350 mW specification.

Compliance Considerations:

All recommended substitute parts are RoHS3 compliant and REACH unaffected. Parts designated with "TR PBFREE" indicate lead-free tape and reel packaging. Selection should account for existing supply chain requirements and manufacturing process compatibility.

Frequently Asked Questions (FAQ)

Q: Can MMBZ5248BLT1G (225 mW) be used as a direct replacement for MMBZ5248B (350 mW)?

A: The MMBZ5248BLT1G is functionally compatible for applications where power dissipation does not exceed 225 mW. The zener voltage (18 V), tolerance (±5%), impedance (21 Ohms), and forward voltage characteristics are identical. Applications requiring the full 350 mW dissipation capability must use 350 mW rated alternatives.

Q: What is the difference between impedance values of 21 Ohms and 45 Ohms?

A: Both impedance values are within acceptable zener diode specifications. The 21 Ohms impedance (MMBZ5248B, CMPZ5248B, MMBZ5248BLT variants) provides lower dynamic impedance. The 45 Ohms impedance (BZX84 series, CZRT55C18-G) is acceptable for general applications. Selection depends on circuit requirements for voltage regulation stability.

Q: Are BZX84C18 and MMBZ5248B interchangeable?

A: Yes, BZX84C18 variants (BZX84C18 TR PBFREE, BZX84C18-TP) are electrically compatible with MMBZ5248B. Both maintain 18 V zener voltage, ±5% tolerance, 350 mW power rating, and 900 mV forward voltage. The primary difference is impedance (45 Ohms vs. 21 Ohms) and manufacturer. Physical package (SOT-23-3) is identical.

Q: What does "TR PBFREE" designation indicate?

A: "TR PBFREE" indicates Tape & Reel packaging with lead-free (PbFree) solder composition. This designation confirms RoHS compliance and is suitable for automated assembly processes requiring lead-free components.

Q: Can BZX84B18-TP (±2% tolerance) replace MMBZ5248B (±5% tolerance)?

A: Yes, BZX84B18-TP is a suitable replacement. The ±2% tolerance is tighter than the original ±5% specification, providing improved voltage accuracy. All other electrical parameters (18 V zener voltage, 350 mW power, 900 mV forward voltage) are compatible.

Q: Is SZMMBZ5248BLT1G suitable for automotive applications?

A: Yes, SZMMBZ5248BLT1G is qualified to AEC-Q101 automotive standard and is suitable for automotive applications. However, it has a 225 mW power rating rather than the original 350 mW. Verify that application power requirements do not exceed 225 mW.

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

A: The -65°C minimum operating temperature provides extended low-temperature performance compared to -55°C. For applications operating in extreme cold environments, parts rated to -65°C (MMBZ5248BLT1G, MMBZ5248BLT3G, BZX84C18 TR PBFREE, CMPZ5248B TR PBFREE, CZRT55C18-G, SZMMBZ5248BLT1G) are recommended.

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

A: Yes, all listed substitute parts are available in Tape & Reel (TR) packaging suitable for automated assembly. The MMBZ5248B original part does not specify packaging format in the provided data.

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