CMHZ5242B-TR-PBFREE - 12V 500mW Zener Diode SOD-123 | Central Semiconductor
MPN: CMHZ5242B-TR-PBFREE β Last Time Buy| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.37 | $0.37 |
| 10 | $0.3 | $3.00 |
| 100 | $0.22 | $22.00 |
| 500 | $0.17 | $85.00 |
| 1,000 | $0.12 | $120.00 |
CMHZ5242B-TR-PBFREE Overview
A Zener diode is a diode type engineered to operate in reverse breakdown, where it maintains a nearly constant voltage across its terminals over a wide range of currents. Within the power management hierarchy, it functions as a shunt voltage regulator, a voltage reference, and a clamp or protection element, sitting alongside linear regulators and switching converters in the broader family of voltage regulation solutions.
Key features include a nominal Zener voltage of 12 V with an 11.4 V to 12.6 V tolerance window, a specified test current of 20 mA, and a low dynamic impedance of 30 ohms that keeps regulation tight under varying load. Reverse leakage is just 1 uA at 9.1 V, and the device is rated for operation up to 150 C, giving substantial thermal headroom for industrial environments. The PBFREE suffix confirms lead-free, RoHS-oriented construction.
The CMHZ5221B Series from Central Semiconductor is manufactured as a high quality surface mount voltage regulator designed for industrial, commercial, entertainment, and computer applications. The silicon planar construction delivers stable breakdown characteristics, and the small SOD-123 outline minimizes board area while supporting automated pick-and-place assembly.
Typical applications include 12 V rail clamping and transient suppression, low-current shunt regulation for microcontroller and sensor bias rails, voltage reference generation for comparators, and protection of inputs on industrial and computer equipment. Its 500 mW rating covers most logic-level clamp duties without a heatsink.
Design consideration: derate power dissipation above 50 C ambient and size the series resistor so that worst-case input voltage with an open load does not exceed the 500 mW rating; at 12 V this limits continuous Zener current to roughly 40 mA.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for CMHZ5242B-TR-PBFREE β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with CMHZ5242B-TR-PBFREE (same form factor and footprint) β differing in Operating Temperature, Package, Packaging, Series.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
CMHZ5241B-TR-PBFREE
β Drop-Inπ Reference alternative (not in catalog)
CMHZ5242B-BK-PBFREE
β Drop-Inβ In Stock
$0.1 / Unit
View Datasheet βCMHZ5243B-TR-PBFREE
β Drop-Inπ Reference alternative (not in catalog)
MMSZ5242B-7-F
β Drop-Inπ Reference alternative (not in catalog)
MMSZ5242BT1G
β Drop-Inπ Reference alternative (not in catalog)
BZT52C12-7-F
β Drop-Inπ Reference alternative (not in catalog)
CMHZ5242B-TR-PBFREE Maximum Ratings & Electrical Characteristics
| Zener Voltage (Nominal) | 12 V |
| Zener Voltage Tolerance | +/-5% (11.4 V to 12.6 V) |
| Power Dissipation | 500 mW |
| Test Current | 20 mA |
| Dynamic Impedance (Zt) | 30 ohms |
| Reverse Leakage Current | 1 uA @ 9.1 V |
| Configuration | Single Zener |
| Mounting Type | Surface Mount |
| Package | SOD-123 |
| Operating Temperature | up to 150 C |
| Lead Free | Yes (PBFREE) |
| Series | CMHZ5221B |
| Applications | Industrial, commercial, entertainment, computer |
| Packaging | Tape & Reel (TR) |
CMHZ5242B-TR-PBFREE Pin Configuration
| Pin 1 | Kathode (K) β Cathode - connect to the more positive potential in reverse-bias regulation; bar/marked end of SOD-123 |
| Pin 2 | Anode (A) β Anode - connect to the more negative potential for Zener regulation |
Typical Applications
CMHZ5242B-TR-PBFREE is suitable for 6 applications: 12V Rail Overvoltage Clamping, Low-Cost Shunt Voltage Regulation, Comparator and ADC Voltage Reference, Signal Line Protection in Computer Equipment, Bias Network Stabilization for Sensors, Automotive and Appliance Auxiliary Rails.
12V Rail Overvoltage Clamping
The CMHZ5242B-TR-PBFREE serves as a shunt clamp across 12 V industrial and computer power rails, diverting fault energy when voltage exceeds its 11.4 V to 12.6 V breakdown window. Its 500 mW rating absorbs moderate transient energy, while the 30 ohm dynamic impedance keeps the clamped voltage from rising sharply as current increases. Because it is a two-terminal SOD-123 device, it can be placed directly across the rail near the sensitive load with minimal board area. For high-energy faults, pair it with a series resistor or fuse so sustained current stays under roughly 40 mA, the estimated maximum continuous Zener current at 12 V.
Recommended
Low-Cost Shunt Voltage Regulation
In cost-sensitive industrial and entertainment products, the CMHZ5242B works as a simple shunt regulator: a series resistor from a higher rail feeds the 12 V Zener, which holds the output near 12 V for light loads. The specified 20 mA test current and 30 ohm dynamic impedance deliver stable regulation, and 1 uA reverse leakage at 9.1 V minimizes bias-drain in always-on circuits. Compared with a linear regulator IC, the solution needs only two components and no output capacitor for stability, at the cost of +/-5% accuracy and continuous standing current through the resistor. Derate dissipation above 50 C ambient to stay within the 500 mW envelope.
Recommended
Comparator and ADC Voltage Reference
Where a microcontroller ADC or comparator needs a coarse 12 V reference or threshold, the CMHZ5242B provides a stable breakdown voltage at milliamp-level currents. The +/-5% tolerance suits threshold detection and window comparators, and the 30 ohm dynamic impedance limits reference shift as bias current varies with supply ripple. Feeding the diode from a clean rail through a resistor with a 10 mA to 20 mA bias keeps it firmly in breakdown. For finer accuracy, pair two Zeners back-to-back or calibrate the threshold in firmware. Its 150 C rating allows reference operation inside sealed industrial enclosures without forced cooling.
Recommended
Signal Line Protection in Computer Equipment
On data and control lines in computer and peripheral equipment, the CMHZ5242B clamps induced surges and ESD-follow-on overvoltage to approximately 12 V before it reaches sensitive IC inputs. Placed from the line to ground after a series current-limiting element, its low 1 uA leakage at 9.1 V preserves signal integrity on high-impedance nodes, and the SOD-123 outline fits dense I/O layouts for automated assembly. The device responds instantly to overvoltage since it is a passive clamp with no trigger threshold. For lines that idle above 12.6 V, select the next voltage code in the CMHZ5221B Series instead to avoid continuous conduction.
Recommended
Bias Network Stabilization for Sensors
Sensor bridges and transducer bias circuits in industrial monitoring equipment benefit from a fixed 12 V bias that does not drift with supply variation. The CMHZ5242B, biased at its 20 mA test current through a series resistor, provides that rail with 30 ohm dynamic impedance, rejecting input ripple effectively at DC and low frequencies. Operating up to 150 C, it tolerates enclosure temperature swings that would challenge electrolytic-referenced solutions. Because the Zener draws current continuously, this approach suits mains-powered or vehicle-powered systems rather than battery nodes; for battery designs, a micropower reference or a higher-value series resistor with a lighter load is preferable to extend runtime.
Recommended
Automotive and Appliance Auxiliary Rails
In appliance and vehicle-derived 12 V systems, the CMHZ5242B establishes a local reference or clamps auxiliary loads such as indicator LEDs and relay driver bias. The 500 mW rating, 150 C operation, and SOD-123 surface mount construction withstand under-hood-adjacent and enclosed-appliance temperatures with simple copper-pad cooling. Its +/-5% window means designers should treat it as a coarse reference: 11.4 V to 12.6 V covers most indicator and relay-bias needs but not precision measurement. Given discontinuation notice PDN01284, long-life automotive and appliance programs should dual-source with the SOD-123 MMSZ5242B equivalents from the outset to protect future production.
Recommended
Recommended Products Summary
Engineering reference data for CMHZ5242B-TR-PBFREE β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | CMHZ5241B-TR-PBFREE | MMSZ5242B-7-F | MMSZ5242BT1G | BZT52C12-7-F |
|---|---|---|---|---|---|
| Package | SOD-123 | SOD-123 - same | SOD-123 - same | SOD-123 - same | SOD-123 - same |
| Brand | Central Semiconductor | Central Semiconductor | Diodes Incorporated | onsemi | Diodes Incorporated |
| Zener Voltage | 12 V | 11 V | 12 V | 12 V | 12 V |
| Power Dissipation | 500 mW | 500 mW | 500 mW | 500 mW | 400 mW |
| Tolerance | +/-5% | +/-5% | +/-5% | +/-5% | +/-5% |
| Lifecycle Status | Last time buy (PDN01284) | Active (verify) | Active | Active | Active |
| Lead Free | Yes (PBFREE) | Yes | Yes | Yes | Yes |
Key Differentiators
- Full 500 mW dissipation in SOD-123 (vs BZT52C12-7-F)
- Supply-security risk from discontinuation (vs MMSZ5242B-7-F)
- Specified 20 mA test current with 30 ohm Zt (vs CMHZ5241B-TR-PBFREE)
Design Notes
Derate the 500 mW rating above the reference ambient. Estimated example: at 12 V Zener voltage, 500 mW corresponds to about 40 mA continuous current; a 30 C rise above the derating start point reduces allowable dissipation proportionally under the standard SOD-123 derating slope. Size the series resistor for worst case load-off: with the load open, all resistor current flows through the diode. Check both corners (11.4 V and 12.6 V tolerance units) when computing resistor power and clamp margins.
Give the SOD-123 pads generous copper area to act as the heatsink, since the package has no thermal pad - thermal performance depends almost entirely on pad size and plane connection. Place the Zener directly across the node being clamped, with the series resistor between the source and this node to guarantee fault current limiting. Keep traces carrying fault current short and at least 0.3 mm wide. The cathode bar marking on the package must align with the more positive potential; reversed installation leaves the load unprotected.
The most frequent design error is treating a +/-5% Zener as a precision reference: the CMHZ5242B can legitimately regulate anywhere from 11.4 V to 12.6 V, and the voltage also shifts with Zener current through its 30 ohm dynamic impedance (about +/-60 mV per 2 mA of current change). Another pitfall is using it on rails that idle above 12.6 V, causing continuous conduction and premature failure. Finally, PDN01284 discontinuation means new designs must qualify MMSZ5242B-type equivalents before release.
Compliance Information
PBFREE suffix indicates lead-free construction per Central Semiconductor product data. REACH, halogen-free, and conflict-minerals status not stated in provided data.
