CMHZ5242B-BK-PBFREE - 12V 500mW SOD-123 Zener Diode | Central Semiconductor
MPN: CMHZ5242B-BK-PBFREE ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.39 | $0.39 |
| 10 | $0.31 | $3.10 |
| 100 | $0.19 | $19.00 |
| 500 | $0.13 | $65.00 |
| 1,000 | $0.1 | $100.00 |
CMHZ5242B-BK-PBFREE Overview
A Zener diode is a special class of voltage-regulator diode engineered to conduct in reverse breakdown at a precisely controlled voltage without damage, making it the simplest building block in the voltage-regulator and voltage-reference hierarchy of power-management components. Unlike rectifier diodes, a Zener maintains a nearly constant reverse voltage across a wide range of reverse current, which allows it to clamp, level-shift, or generate reference rails in any circuit needing a fixed potential.
Key specifications of the CMHZ5242B include a dynamic impedance (Zzt) of only 30 ohms at the test current, a low reverse leakage of 1 uA at 9.1 V, and a 500 mW power dissipation rating at 25 C, with operation permitted up to a 150 C junction temperature. The B suffix denotes the tighter 5% voltage tolerance over the base CMHZ series, and the PBFREE designation confirms lead-free, RoHS-aligned construction.
The device belongs to the CMHZ5221B Series, which spans 2.4 V through 75 V in the same SOD-123 outline, letting designers scale one qualified footprint across an entire range of clamp and reference voltages. Central Semiconductor manufactures the series specifically for industrial, commercial, entertainment and computer applications per the manufacturer datasheet.
Typical applications include 12 V rail clamping on industrial inputs, low-current shunt references for op-amp bias, protection of MOSFET gates against overvoltage, and start-up bias supplies in AC-DC converters.
Design-wise, derate the 500 mW rating linearly above 25 C and size the series resistor so worst-case current keeps dissipation within limits; the 30 ohm dynamic impedance means regulation quality depends on a healthy bias current.
This page adds distributor pricing tiers, drop-in alternatives, and practical design notes that the bare manufacturer datasheet does not provide.
Drop-in alternatives for CMHZ5242B-BK-PBFREE — 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-BK-PBFREE (same form factor and footprint) — differing in Operating Temperature, Package, Packaging, Series.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
CMHZ5242B-TR-PBFREE
✅ Drop-In✓ In Stock
$0.12 / Unit
View Datasheet →CMHZ5242B-TR
✅ Drop-In📋 Reference alternative (not in catalog)
CMHZ5242B-BK-PBFREE Maximum Ratings & Electrical Characteristics
| Zener Voltage (Nominal) | 12 V |
| Zener Voltage Range (Vz @ Izt) | 11.4 V to 12.6 V |
| Voltage Tolerance | ±5% |
| Power Dissipation | 500 mW |
| Test Current (Izt) | 20 mA |
| Dynamic Impedance (Zzt) | 30 ohms |
| Reverse Leakage Current (Ir) | 1 uA @ 9.1 V |
| Configuration | Single Zener |
| Mounting Type | Surface Mount |
| Package | SOD-123, 2-Pin |
| Operating Temperature | up to +150 C (junction) |
| Series | CMHZ5221B (2.4 V thru 75 V) |
| Packaging | Bulk (BK) |
| Polarity | Unidirectional |
| Lead Free / RoHS | Yes / PBFREE |
| Typical Applications | Industrial, commercial, entertainment, computer |
CMHZ5242B-BK-PBFREE Pin Configuration
| Pin 1 | Cathode — Zener cathode - connect to the more positive node for reverse-breakdown (regulating) operation |
| Pin 2 | Anode — Zener anode - connect to ground or the more negative node |
Typical Applications
CMHZ5242B-BK-PBFREE is suitable for 6 applications: Industrial 12V Input Clamping, MOSFET Gate Overvoltage Protection, Low-Current Shunt Voltage Reference, Computer Peripheral and Entertainment Electronics, AC-DC Converter Start-Up Bias, Automotive-Adjacent Sensor and Actuator Modules.
Industrial 12V Input Clamping
The CMHZ5242B-BK-PBFREE fits industrial input protection because its 11.4 V to 12.6 V breakdown window tracks nominal 12 V rails closely while the 500 mW rating absorbs moderate fault transients. Wired from the protected node to ground with an upstream series resistor, it conducts within microseconds of an overvoltage event and holds the node near 12 V. The 1 uA leakage at 9.1 V keeps normal operation unaffected, and the SOD-123 package fits dense terminal-block and PLC I/O boards where through-hole DO-35 diodes will not fit.
Recommended
MOSFET Gate Overvoltage Protection
Power MOSFET gates must stay within a ±20 V (or ±10 V for logic-level types) limit; the CMHZ5242B-BK-PBFREE clamps gate drive overshoot at 12 V, comfortably inside the safe range of standard threshold MOSFETs. Its 30 ohm dynamic impedance limits voltage rise during fast switching events, and the 500 mW rating handles repetitive low-energy transients in motor-drive and DC-DC applications. The 2.4 V to 75 V CMHZ5221B Series lets designers scale the same SOD-123 footprint to clamp 15 V or 18 V gates using the CMHZ5246B or CMHZ5248B siblings.
Recommended
Low-Current Shunt Voltage Reference
For non-critical 12 V bias rails - op-amp bias points, comparator thresholds, level shifters - the CMHZ5242B-BK-PBFREE forms a one-component shunt reference. Biased at a few milliamperes through a series resistor, its 30 ohm impedance yields millivolt-level line regulation for static loads. The 5% tolerance suits applications accepting coarse accuracy; where tighter tolerance or temperature stability is needed, a TL431-class shunt reference replaces it. The bulk BK packaging suits hand-placed analog prototype and low-volume instrumentation assembly.
Recommended
Computer Peripheral and Entertainment Electronics
Central Semiconductor explicitly targets the CMHZ5221B Series - including the CMHZ5242B - at industrial, commercial, entertainment and computer applications. In set-top boxes, audio accessories, and peripheral boards, the 12 V clamp protects accessory power inputs and switch-mode secondary rails, while the SOD-123 outline supports high-density reflow assembly. The PBFREE lead-free construction meets global environmental regulations for consumer products shipped into the EU and other RoHS-regulated markets, removing compliance risk from high-volume entertainment hardware.
Recommended
AC-DC Converter Start-Up Bias
Off-line and auxiliary power converters frequently use a Zener-clamped start-up rail charged through a high-value resistor from the bulk capacitor. The CMHZ5242B-BK-PBFREE's 500 mW rating and 150 C junction capability suit this continuous-dissipation duty once the converter's auxiliary winding takes over and the start-up clamp current falls. The 12 V point matches common PWM controller VCC UVLO thresholds, and the 1 uA leakage minimizes standing drain on standby power budgets in energy-efficiency-regulated power supplies.
Recommended
Automotive-Adjacent Sensor and Actuator Modules
In 12 V-nominal vehicular-derived systems - agricultural, marine, and light-industrial modules not requiring AEC-Q100 qualification - the CMHZ5242B-BK-PBFREE clamps load-dump-filtered supply nodes and sensor excitation lines. Its 12.6 V maximum breakdown stays below the 13.5 V charging-system floor in off-state, while 500 mW dissipation and the SOD-123 package's solder-joint reliability handle vibration-prone environments when a robust land pattern is used per the manufacturer datasheet recommendations.
Recommended
Recommended Products Summary
Engineering reference data for CMHZ5242B-BK-PBFREE — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | CMHZ5242B-TR-PBFREE | CMHZ5242B-TR | CMHZ5233B-TR-PBFREE |
|---|---|---|---|---|
| Package | SOD-123 | SOD-123 - same | SOD-123 - same | SOD-123 - same |
| Brand | Central Semiconductor Corp | Central Semiconductor Corp | Central Semiconductor Corp | Central Semiconductor Corp |
| Zener Voltage (Nominal) | 12 V | 12 V | 12 V | 6 V |
| Power Dissipation | 500 mW | 500 mW | 500 mW | 500 mW |
| Tolerance | ±5% | ±5% | ±5% | ±5% |
| Packaging Format | Bulk (BK) | Tape & Reel | Tape & Reel | Tape & Reel |
Key Differentiators
- Same electrical spec in bulk packaging for hand assembly (vs CMHZ5242B-TR-PBFREE)
- 150 C maximum junction temperature (vs CMHZ5233B-TR-PBFREE)
- 30 ohm low dynamic impedance at 12 V (vs CMHZ5233B-TR-PBFREE)
Design Notes
The 500 mW rating applies at 25 C and must be derated linearly toward the 150 C maximum junction temperature. As an estimate, with a typical SOD-123 theta_JA near 300 C/W on a minimum pad, a continuous 150 mW dissipation raises the junction roughly 45 C above ambient - leaving adequate margin at 70 C surroundings but not at full rating. Calculate dissipation as Vz x Iz using the worst-case high-source-voltage, low-load, low-Vz corner (11.4 V) and enlarge copper pads or reduce bias current accordingly.
Use a standard SOD-123 land pattern with pads extended toward the body to improve heat spreading; doubling pad area measurably lowers effective theta_JA for clamp duty. Keep the diode's ground return close to the protected node's ground to minimize loop inductance during fast transient clamping. Because the whole CMHZ5221B Series shares the SOD-123 footprint, lay out the board for any series voltage - this permits a late voltage change (e.g., 12 V to 15 V via CMHZ5246B) with a BOM-only edit.
Do not operate the CMHZ5242B in forward-current rectification duty for regulation - its breakdown parameter set applies to reverse operation only. Avoid biasing near the knee: below roughly 1 mA the 12 V part exhibits soft breakdown and effective impedance rises sharply, degrading clamp accuracy. Observe polarity: pin 1 is the cathode per SOD-123 convention - reversed installation simply acts as a 0.7 V forward diode and may not be caught by functional test on low-voltage rails.
Compliance Information
PBFREE designation confirms lead-free construction per Central Semiconductor and distributor listings (DigiKey, Mouser, Arrow, Hotenda). REACH, halogen-free, and conflict-minerals statuses not stated in the provided data.
