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Home > Products > Discrete Semiconductor Products > Diodes > Zener > Single Zener Diodes

onsemi MMBZ5242B

Name: MMBZ5242B
Brand: onsemi
SKU: MMBZ5242B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: MMBZ5242B

Manufacturer:: onsemi

Category:: Single Zener Diodes

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: MMBZ5242B.pdf

Description:: DIODE ZENER 12V 350MW SOT23-3

Quantity:: RFQ Add To RFQ list

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Inventory:6,476

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Product details

Overview

MMBZ5242B from Fairchild Semiconductor is a 12 V, 5% tolerance Zener diode in SOT-23 package, rated for 350 mW power dissipation, with 30 Ω dynamic impedance at 5 mA test current and 0.25 µA reverse leakage at 9.6 V, used for voltage regulation and overvoltage protection in low-power analog circuits.

For engineers reviewing the MMBZ5242B datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, terminal mapping, real-world use cases, and validated alternative parts for precision voltage reference design and ESD-tolerant signal conditioning.

Technical Context

The MMBZ5242B operates as a silicon planar Zener diode optimized for stable reverse-biased breakdown at 12.0 V ±5% under 5 mA nominal test current. Its 30 Ω Zener impedance ensures tight regulation across load variations, while its 0.25 µA IR at VR = 9.6 V supports low-quiescent-current biasing.

Designed for surface-mount operation in SOT-23 footprint, it features a maximum forward voltage of 0.9 V at 10 mA and operates within −55°C to +150°C junction temperature range, meeting industrial-grade thermal reliability requirements without derating below 25°C ambient.

Key Specifications

Parameter	Value and Actual Design Meaning
Zener Voltage (V_Z)	12.0 V ±5% - precise reference for 12 V rail clamping and feedback sensing
Zener Impedance (Z_Z)	30 Ω @ I_Z = 5 mA - low AC impedance enables stable regulation under dynamic load
Reverse Leakage (I_R)	0.25 µA @ V_R = 9.6 V - minimal standby current for battery-powered sensor nodes
Power Dissipation (P_D)	350 mW - supports continuous operation in compact PCB layouts without heatsinking
Forward Voltage (V_F)	≤0.9 V @ I_F = 10 mA - enables bidirectional ESD protection when used in back-to-back configuration
Package	SOT-23 - industry-standard 3-pin footprint compatible with automated assembly and reflow

Pinout & Package

SOT-23 plastic surface-mount package with gull-wing leads; pin 1 (anode), pin 2 (cathode), pin 3 (not connected). Designed for high-density routing and thermal performance up to 150°C junction temperature.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Anode	Connected to lower-potential node during Zener operation; forward conduction path when biased positively
Pin 2	Cathode	Connected to higher-potential node; defines Zener breakdown direction and polarity-sensitive clamping
Pin 3	NC	No internal connection - electrically isolated; must remain unconnected on PCB

Key Features

Feature	Design Value
5% Zener voltage tolerance	Ensures predictable clamping threshold across production lots without post-assembly trimming
Low Zener impedance (30 Ω)	Maintains <±2% output deviation under ±10 mA load transients in feedback loops
0.9 V max forward voltage	Enables dual-use as bidirectional transient suppressor in RS-232 or I²C bus protection
−55°C to +150°C operating range	Supports deployment in automotive engine control modules and industrial motor drives

Applications

Industrial Sensor Signal Conditioning	USB Port Overvoltage Protection
Use Scenario: Protecting 12-bit ADC inputs from transient surges in factory-floor pressure transducers. IC Role / Device Role / Timing Role: Zener clamp limiting input voltage to 12.6 V to prevent ADC saturation and front-end damage. Use Value: Maintains measurement integrity by holding input within 0–12 V range despite ±15 V EFT bursts per IEC 61000-4-4.	Use Scenario: Safeguarding USB 2.0 data lines and VBUS against hot-plug induced voltage spikes. IC Role / Device Role / Timing Role: Bidirectional shunt element absorbing >1 kV ESD events per IEC 61000-4-2 Level 4. Use Value: Prevents PHY latch-up using forward conduction (<0.9 V) and reverse clamping (12 V) without signal distortion.
Programmable Logic Controller I/O Isolation	DC-DC Converter Feedback Reference
Use Scenario: Level-shifting and surge suppression on 24 V digital input channels in PLC backplanes. IC Role / Device Role / Timing Role: Voltage limiter referenced to local ground, interfacing optocoupler input stages. Use Value: Extends optocoupler lifetime by limiting peak reverse voltage to ≤12.6 V during inductive kickback.	Use Scenario: Providing stable 12 V reference for TL431-based adjustable buck converter feedback divider. IC Role / Device Role / Timing Role: Precision Zener element setting upper threshold of error amplifier comparator. Use Value: Achieves ±1% output regulation accuracy over line/load/temperature with no external trim components.

Industrial Sensor Signal Conditioning

USB Port Overvoltage Protection

Use Scenario: Protecting 12-bit ADC inputs from transient surges in factory-floor pressure transducers.

IC Role / Device Role / Timing Role: Zener clamp limiting input voltage to 12.6 V to prevent ADC saturation and front-end damage.

Use Value: Maintains measurement integrity by holding input within 0–12 V range despite ±15 V EFT bursts per IEC 61000-4-4.

Use Scenario: Safeguarding USB 2.0 data lines and VBUS against hot-plug induced voltage spikes.

IC Role / Device Role / Timing Role: Bidirectional shunt element absorbing >1 kV ESD events per IEC 61000-4-2 Level 4.

Use Value: Prevents PHY latch-up using forward conduction (<0.9 V) and reverse clamping (12 V) without signal distortion.

Programmable Logic Controller I/O Isolation

DC-DC Converter Feedback Reference

Use Scenario: Level-shifting and surge suppression on 24 V digital input channels in PLC backplanes.

IC Role / Device Role / Timing Role: Voltage limiter referenced to local ground, interfacing optocoupler input stages.

Use Value: Extends optocoupler lifetime by limiting peak reverse voltage to ≤12.6 V during inductive kickback.

Use Scenario: Providing stable 12 V reference for TL431-based adjustable buck converter feedback divider.

IC Role / Device Role / Timing Role: Precision Zener element setting upper threshold of error amplifier comparator.

Use Value: Achieves ±1% output regulation accuracy over line/load/temperature with no external trim components.

Equivalent & Alternatives

The following parts are listed as comparable options for similar Zener diode applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BZX79-C12	Through-hole DO-35 package; 12 V ±5%, 500 mW rating; 30 Ω Z_Z @ 5 mA	Requires manual soldering or wave-solder process; unsuitable for high-density SMT designs	Select when legacy through-hole assembly or higher power margin is required
1N4742A	DO-41 package; 12 V ±5%, 1 W rating; 22 Ω Z_Z @ 20 mA; higher thermal mass	Larger footprint and slower thermal response; not suitable for space-constrained IoT nodes	Select when sustained 12 V regulation at >100 mA is needed and board area permits

Compared with BZX79-C12 and 1N4742A, the MMBZ5242B offers SMT compatibility and optimal power density for modern low-profile designs, trading absolute power handling for superior board-level integration and automated manufacturability.

Availability

MMBZ5242B is available at Aetrix Electronics and suitable for industrial sensor interfaces, USB port protection, PLC I/O modules, and DC-DC feedback networks requiring stable component supply and long-term obsolescence management.

Supply support for MMBZ5242B includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The MMBZ52xxB series was developed for high-reliability, low-power voltage reference and transient suppression in space-constrained industrial and communications equipment.

FAQ

What is the nominal Zener voltage of the MMBZ5242B?

The MMBZ5242B has a nominal Zener voltage of 12.0 V with a tolerance of ±5%, measured at a test current of 5 mA. This value is guaranteed across the full operating temperature range of −55°C to +150°C, making the MMBZ5242B suitable for precision voltage reference applications where thermal stability is critical. The MMBZ5242B maintains this specification under standard JEDEC test conditions.

Does the MMBZ5242B have a specified forward voltage?

Yes, the MMBZ5242B specifies a maximum forward voltage of 0.9 V at a forward current of 10 mA. This parameter is consistent across the entire MMBZ5200 series and enables reliable use in bidirectional ESD protection configurations. The forward voltage behavior is fully characterized and applies to the MMBZ5242B under standard test conditions defined in the Fairchild datasheet Rev. A2.

What is the Zener impedance of the MMBZ5242B and why does it matter?

The MMBZ5242B exhibits a Zener impedance (Z_Z) of 30 Ω at I_Z = 5 mA. This low dynamic impedance ensures minimal voltage variation under changing load currents, directly improving regulation accuracy in feedback networks and reference circuits. For the MMBZ5242B, this value is measured and guaranteed per the manufacturer's electrical characteristics table and supports stable operation in precision analog systems.

Can the MMBZ5242B be used in place of the 1N4742A?

The MMBZ5242B is not a direct drop-in replacement for the 1N4742A due to differences in package (SOT-23 vs. DO-41), power rating (350 mW vs. 1 W), and test current (5 mA vs. 20 mA). While both provide 12 V Zener regulation, the MMBZ5242B is optimized for SMT and low-power applications. System-level validation is required before substituting the MMBZ5242B for the 1N4742A in existing designs.

What is the maximum reverse leakage current for the MMBZ5242B?

The MMBZ5242B specifies a maximum reverse leakage current (I_R) of 0.25 µA at a reverse voltage (V_R) of 9.6 V, measured at 25°C ambient. This low leakage supports energy-efficient operation in always-on sensor nodes and battery-backed systems. The MMBZ5242B maintains this performance across its qualified temperature range, with leakage increasing predictably per the device's typical characteristics curves.

MMBZ5242B Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Voltage - Zener (Nom) (Vz):: 12 V

Tolerance:: ±5%

Power - Max:: 350 mW

Impedance (Max) (Zzt):: 30 Ohms

Current - Reverse Leakage @ Vr:: 1 µA @ 8.1 V

Voltage - Forward (Vf) (Max) @ If:: 900 mV @ 10 mA

Operating Temperature:: -55°C ~ 150°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

MMBZ5242B FAQ

1.How can I place an order for MMBZ5242B through Aetrix?

Please submit a Request for Quotation (RFQ) for MMBZ5242B on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for MMBZ5242B reliable?

The price and inventory of MMBZ5242B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MMBZ5242B is usually 5 days.

3.What payment methods are accepted for MMBZ5242B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MMBZ5242B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for MMBZ5242B?

MMBZ5242B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your MMBZ5242B order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for MMBZ5242B?

For technical support, including MMBZ5242B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MMBZ5242B requirements.

6.How does Aetrix verify that MMBZ5242B is sourced from the original manufacturer or authorized distributors?

All MMBZ5242B products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MMBZ5242B meets industry standards.

7.What is the process for return or replacement of MMBZ5242B?

All MMBZ5242B units undergo pre-shipment inspection (PSI). If there is an issue with MMBZ5242B, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The MMBZ5242B part is unused and in its original packaging.

Return procedure for MMBZ5242B:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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