CMHZ5242B - 12V 500mW SOD-123 Zener Diode | Central Semiconductor
MPN: CMHZ5242B β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.12 | $0.12 |
| 10 | $0.09 | $0.90 |
| 100 | $0.06 | $6.00 |
| 500 | $0.045 | $22.50 |
| 1,000 | $0.035 | $35.00 |
CMHZ5242B Overview
A zener diode is a voltage-reference device that conducts in reverse breakdown at a precisely defined voltage, making it a fundamental building block within the broader hierarchy of discrete semiconductors -> diodes -> voltage references. Unlike rectifier diodes, zener diodes are deliberately operated in reverse breakdown, where the voltage across the device remains nearly constant over a wide range of reverse current. This property enables simple shunt voltage regulation, voltage clamping, and level shifting without the complexity of an active regulator IC.
The CMHZ5242B belongs to Central Semiconductor's CMHZ series, a surface mount family spanning zener voltages from 2.4 V through 75 V (with related datasheet variants listing up to 200 V) at 500 mW, offering designers a single sourcing family for many rail values. The 12 V rating makes it well suited to clamping 12 V logic rails, protecting gates and MOSFET source pins, and generating reference levels for comparator thresholds. Its 5% tolerance covers the B-suffix grade, appropriate for non-critical clamping rather than precision references.
Technically, the device is a silicon planar zener operating below roughly 7 V zener ratings via Zener breakdown and above via avalanche breakdown; a 12 V device sits in the transition region where the temperature coefficient is near minimum. Reverse leakage at 85% of rated voltage is in the low microamp range, and dynamic impedance is modest for the family class.
Typical applications include input protection for microcontroller GPIOs, MOSFET gate-source clamping in motor-drive circuits, low-cost shunt regulators on 12 V industrial rails, and ESD/overvoltage clamping in consumer and automotive accessory boards.
Design consideration: size the series resistor so worst-case load current plus zener bias current keeps power below 500 mW derated for ambient temperature, and note that zener tolerance plus dynamic impedance sets the achievable rail accuracy.
This page adds distributor availability, drop-in alternatives across onsemi, Diodes Incorporated, MCCC and Nexperia, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for CMHZ5242B β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
MMSZ5242B
β Drop-Inπ Reference alternative (not in catalog)
MMSZ5242B-7-F
β Drop-Inπ Reference alternative (not in catalog)
MMSZ5242B-TP
β Drop-Inπ Reference alternative (not in catalog)
TZMC12
β Drop-Inπ Reference alternative (not in catalog)
BZT52C12-7-F
β Drop-Inπ Reference alternative (not in catalog)
BZT52C12
β Drop-Inπ Reference alternative (not in catalog)
CMHZ5242B Maximum Ratings & Electrical Characteristics
| Zener Voltage (Nominal) | 12 V |
| Zener Voltage Tolerance | Β±5% |
| Power Dissipation | 500 mW |
| Configuration | Single Zener |
| Mounting Type | Surface Mount |
| Package / Case | SOD-123 |
| Marking Code | CH2 |
| Product Family | CMHZ series (2.4 V to 75 V, 500 mW) |
| Voltage - Zener (Nom) | 12 V |
| Lead-Free Status | PBFREE (lead-free per DigiKey listing) |
| RoHS Status | Compliant (PBFREE suffix) |
| Packaging Options | Tape & Reel (TR) and Bulk (BK) |
| Polarity | Unidirectional |
CMHZ5242B Pin Configuration
| Pin 1 | Cathode β Zener cathode (band-marked end); reverse voltage applied here for zener operation |
| Pin 2 | Anode β Zener anode; connect to ground in clamping/regulation circuits |
Typical Applications
CMHZ5242B is suitable for 6 applications: Microcontroller GPIO Overvoltage Clamping, MOSFET Gate-Source Voltage Clamp, Low-Cost 12 V Shunt Regulation, Inductive Kickback Suppression in Relay and Solenoid Drivers, Battery-Powered 12 V System Protection, Comparator and Sensor Threshold Referencing.
Microcontroller GPIO Overvoltage Clamping
The CMHZ5242B's precise 12 V breakdown makes it a compact clamp for protecting microcontroller inputs and 12 V-tolerant GPIO lines from transient overvoltage. In a typical circuit the zener sits from the protected node to ground with a series resistor limiting fault current; the 500 mW rating absorbs roughly 40 mA continuous (500 mW / 12 V, estimated), which is ample for short inductive kickback events. Because the device is a 0.9 mm x 1.2 mm-footprint SOD-123, it fits directly on dense I/O headers without layout changes. Its Β±5% tolerance is irrelevant for protection (only clamping threshold placement matters), and low reverse leakage keeps signal integrity intact on high-impedance sense lines. Place the diode within a few millimeters of the connector pin to minimize parasitic inductance during fast transients.
Recommended
MOSFET Gate-Source Voltage Clamp
Power MOSFETs with 20 V maximum gate-source ratings are routinely protected with a 12 V zener such as the CMHZ5242B between gate and source. When gate-driver overshoot from parasitic inductance exceeds the 12 V zener voltage, the device conducts and clamps VGS to a safe level, preventing gate-oxide failure in motor drives, half-bridge converters, and relay drivers. The 500 mW SOD-123 package handles the short, energy-limited overshoot events typical of gate paths; the gate-drive source impedance limits continuous current into the zener. Because the clamp is local to the gate-source terminals, the CMHZ5242B's small package mounts directly across the MOSFET pads. Designers should verify driver current capability accounts for the clamped condition, and keep the zener trace loop short to remain effective against nanosecond-scale transients.
Recommended
Low-Cost 12 V Shunt Regulation
In unregulated wall-adapter or auxiliary industrial supplies, the CMHZ5242B works as a shunt regulator: a series resistor feeds the 12 V zener, which holds the node near 12 V for modest load currents. With 500 mW dissipation the bias budget is roughly 40 mA maximum at 25 C (estimated from 500 mW / 12 V), covering microcontroller standby loads, relay coil hold circuits, or LED indicators. The Β±5% tolerance yields a 11.4 V to 12.6 V rail, sufficient for relays, lamps, and logic that tolerate wide input. Unlike an LDO, no output capacitor stability concerns exist, and the circuit survives input surges by simply conducting harder. For better accuracy, use the zener to protect a precision regulator rather than as the reference itself. Account for load-line: output impedance equals the zener dynamic impedance plus the series resistor.
Recommended
Inductive Kickback Suppression in Relay and Solenoid Drivers
When switching relays, solenoids, or small DC motors, the collapsing magnetic field generates a voltage spike that can destroy the switching transistor. A CMHZ5242B across the transistor (or across the coil with appropriate polarity) clamps the flyback voltage to approximately 12 V above the rail, dissipating the stored inductive energy in the zener and coil resistance. The 500 mW rating suits small relays (typically tens of millijoules per switching event at moderate rates); estimate energy as 0.5 * L * I^2 and confirm the average power stays within the derated zener rating at your switching frequency. The SOD-123 package enables placement immediately beside the driver MOSFET, minimizing loop area. This configuration also speeds coil current decay compared to a plain freewheel diode, improving release time in fast-cycling applications.
Recommended
Battery-Powered 12 V System Protection
Lead-acid battery systems (automotive accessory, UPS backup, solar lighting) nominally sit near 12 V but surge well above it during charging transients. The CMHZ5242B provides inexpensive primary clamping on sensor and control boards: held normally below its breakdown knee at battery float voltages (12.6-13.8 V causes small leakage), it conducts only during genuine surges, absorbing energy within its 500 mW continuous / higher pulse capability. Its low profile SOD-123 package suits compact IoT telematics and alarm boards. For full automotive load-dump compliance, pair the zener with a series resistor and consider a higher-power TVS upstream, using the CMHZ5242B for fine, fast local clamping. Verify leakage at 13.8 V continuous bias against the battery system's quiescent-current budget, which for sleep-mode electronics may be only tens of microamps.
Recommended
Comparator and Sensor Threshold Referencing
The CMHZ5242B generates a stable approximate 12 V rail for powering comparator dividers, window detectors, and sensor excitation circuits in industrial monitoring equipment. Fed through a resistor from a 24 V industrial rail, the zener establishes a quiet local supply whose Β±5% absolute accuracy is acceptable because ratiometric measurement - comparing a sensor output against the same reference - cancels the zener tolerance error. Its low dynamic impedance and microamp-level leakage keep divider currents predictable. The SOD-123 footprint allows multiple reference points across a board without regulator ICs, BOM count, or layout overhead. For circuits needing better than 1% absolute accuracy, use the CMHZ5242B only as a pre-regulator or protection element ahead of a precision reference. Ensure the zener bias current (typically 5 mA recommended) dominates the load current to keep regulation stiff.
Recommended
Recommended Products Summary
Engineering reference data for CMHZ5242B β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MMSZ5242B | MMSZ5242B-7-F | TZMC12 | BZT52C12 |
|---|---|---|---|---|---|
| Package | SOD-123 | SOD-123 - same | SOD-123 - same | SOD-123 - same | SOD-123 - same |
| Brand | Central Semiconductor | onsemi | Diodes Incorporated | Nexperia | Nexperia |
| Zener Voltage | 12 V | 12 V | 12 V | 12 V | 12 V |
| Tolerance | Β±5% | Β±5% | Β±5% | Β±5% (C suffix) | Β±5% (C suffix) |
| Power Dissipation | 500 mW | 500 mW | 500 mW | 500 mW (400 mW class per Nexperia listing) | 500 mW |
| Configuration | Single zener | Single zener | Single zener | Single zener | Single zener |
| Mounting Type | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount |
| Family Origin | CMHZ series (Central) | MMSZ series (1N5242B JEDEC derivative) | MMSZ series (1N5242B JEDEC derivative) | TZMC series | BZT52 series |
Key Differentiators
- Central Semiconductor direct sourcing of the classic 1N5242B-family value (vs MMSZ5242B)
- Marking code CH2 enables unambiguous board-level identification (vs MMSZ5242B-7-F)
- Lower-cost availability in small-batch Bulk (BK) packaging (vs TZMC12)
Design Notes
Budget zener current against the 500 mW rating with temperature derating. Estimated: 500 mW at 12 V permits about 41 mA continuous at 25 C, but halve this near 85 C ambient per typical SOD-123 derating. Always use a series resistor sized for worst-case input voltage minus minimum zener current, then confirm resistor power rating. In clamp applications where current flows only during faults, pulse energy rather than continuous power governs - verify against the datasheet surge capability rather than the DC rating.
Place the CMHZ5242B within 2-5 mm of the node being protected (connector pin or MOSFET terminal) and connect cathode (band) to the positive/node side, anode to ground. Use two well-copper-connected pads - SOD-123 thermal performance depends almost entirely on PCB copper area. Avoid long thin traces to the clamp: even 10 nH of trace inductance adds significant overshoot during nanosecond transients, partially defeating the clamp. For I/O arrays, one zener per line or per rail beats one shared clamp for crosstalk isolation.
Three frequent mistakes: (1) using a 5% zener as a precision reference - a CMHZ5242B may output anywhere from 11.4 V to 12.6 V, so feed precision circuits from a real reference IC; (2) ignoring reverse leakage at high temperature, which can exceed the sleep-current budget of battery devices biased near 12-13 V; (3) forgetting that zener voltage is specified at a particular test current - at microamp bias the knee softens and the effective voltage drops well below 12 V. Always check the CMHZ datasheet's IzT and leakage test conditions.
Compliance Information
DigiKey listings carry the PBFREE suffix, indicating lead-free construction and RoHS compliance. No AEC-Q101 automotive qualification is indicated in the available data; REACH and halogen-free status not stated in provided sources.
