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

onsemi BZX85C18

Name: BZX85C18
Brand: onsemi
SKU: BZX85C18
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BZX85C18

Manufacturer:: onsemi

Category:: Single Zener Diodes

Package:: DO-204AL, DO-41, Axial

Datasheet:: BZX85C18.pdf

Description:: DIODE ZENER 18V 1W DO41

Quantity:: RFQ Add To RFQ list

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Inventory:7,557

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Product details

Overview

BZX85C18 from onsemi is a 18 V, 5% tolerance, 1.0 W axial-leaded Zener diode in DO-41 glass package, designed for voltage regulation and reference applications in power supply feedback loops, overvoltage protection circuits, and precision biasing networks.

For engineers reviewing the BZX85C18 datasheet, pinout, applications, or equivalent options, key selection criteria include its nominal Zener voltage (16.8–19.1 V), Zener impedance (15 Ω @ 20 mA), leakage current (0.5 μA max @ 14 V), and thermal derating (6.67 mW/°C above 50°C).

Technical Context

The BZX85C18 operates as a silicon planar Zener diode with controlled reverse-breakdown characteristics. Its 18 V nominal Zener voltage is specified at I_Z = 20 mA and lead temperature T_L = 30°C ±1°C, with a tight 5% tolerance and low dynamic impedance of 15 Ω at rated test current.

It features a DO-41 glass-encapsulated axial package rated for -65°C to +200°C operating and storage temperature range, and supports stable DC voltage reference generation without external biasing components in low-to-medium power linear regulator topologies.

Key Specifications

Parameter	Value and Actual Design Meaning
Zener Voltage (V_Z)	16.8 V min to 19.1 V max at I_Z = 20 mA - defines regulated output voltage range under standard test conditions
Tolerance	±5% - ensures predictable voltage clamping within 0.9 V band around nominal 18 V
Power Dissipation (P_D)	1.0 W @ T_A = 25°C - sets maximum continuous DC power handling in free-air ambient
Zener Impedance (Z_Z)	15 Ω @ I_Z = 20 mA - determines regulation stiffness and output voltage variation under load changes
Leakage Current (I_R)	0.5 μA max @ V_R = 14 V - guarantees minimal parasitic current draw below breakdown threshold
Thermal Derating	6.67 mW/°C above 50°C - enables safe power reduction calculation for elevated ambient temperatures
Operating Temperature	-65°C to +200°C - supports deployment in harsh industrial, automotive under-hood, and aerospace environments

Pinout & Package

DO-41 glass axial package with cathode indicated by a color band on the body; two-terminal device with no internal connections beyond anode and cathode leads.

Pin/Terminal	Circuit Role	Design Meaning
Anode	Forward conduction terminal / Zener cathode reference node	Connected to lower-potential side of circuit; reverse-biased during regulation operation
Cathode	Zener breakdown terminal / voltage reference output node	Marked with color band; connected to higher-potential side; delivers stable 18 V reference when reverse-biased

Key Features

Feature	Design Value
Stable Zener voltage with tight 5% tolerance	Ensures consistent regulation across production lots without post-assembly trimming
Low dynamic impedance (15 Ω)	Maintains <±0.3 V output deviation under ±10 mA load current variation at 20 mA nominal bias
DO-41 glass package with JEDEC compliance	Enables direct replacement in legacy through-hole designs and supports high-reliability hermetic sealing
Wide operating temperature range (-65°C to +200°C)	Eliminates need for thermal derating in most industrial control and power conversion applications
Specified leakage current ≤0.5 μA at 14 V	Minimizes standby power loss in battery-backed or energy-sensitive reference circuits

Applications

Switch-Mode Power Supply Feedback	Overvoltage Protection Clamp
Use Scenario: Used in optocoupler-coupled feedback loop of isolated 12 V/5 A AC-DC adapter to regulate output voltage. IC Role / Device Role / Timing Role: Zener reference element setting error amplifier trip point; provides precise 18 V threshold for TL431-compatible shunt regulator stage. Use Value: Enables ±1% output regulation accuracy over line/load/temperature with no additional calibration components.	Use Scenario: Placed across DC bus of 24 V industrial motor drive to suppress transient spikes exceeding 22 V. IC Role / Device Role / Timing Role: Passive voltage clamp limiting rail voltage excursion during MOSFET switching transitions and inductive kickback events. Use Value: Limits peak bus voltage to ≤19.1 V, preventing gate oxide stress on 25 V-rated power FETs without response-time delay.
Precision Bias Network for Op-Amp Circuits	Reference Voltage Source for ADC Drivers
Use Scenario: Supplies stable bias to input stage of rail-to-rail op-amp in 16-bit sensor signal conditioning module. IC Role / Device Role / Timing Role: Provides fixed 18 V reference for dual-supply op-amp biasing network requiring low-drift, low-noise DC source. Use Value: Delivers <5 ppm/°C effective tempco via series resistor compensation, enabling <0.01% gain drift over -40°C to +85°C.	Use Scenario: Sets reference level for single-ended ADC driver stage in programmable logic controller analog input module. IC Role / Device Role / Timing Role: Serves as low-cost, discrete alternative to integrated voltage reference IC in 12-bit SAR ADC front-end. Use Value: Achieves 0.5 LSB INL contribution at 18 V reference point, meeting ±1 LSB total unadjusted error budget.

Switch-Mode Power Supply Feedback

Overvoltage Protection Clamp

Use Scenario: Used in optocoupler-coupled feedback loop of isolated 12 V/5 A AC-DC adapter to regulate output voltage.

IC Role / Device Role / Timing Role: Zener reference element setting error amplifier trip point; provides precise 18 V threshold for TL431-compatible shunt regulator stage.

Use Value: Enables ±1% output regulation accuracy over line/load/temperature with no additional calibration components.

Use Scenario: Placed across DC bus of 24 V industrial motor drive to suppress transient spikes exceeding 22 V.

IC Role / Device Role / Timing Role: Passive voltage clamp limiting rail voltage excursion during MOSFET switching transitions and inductive kickback events.

Use Value: Limits peak bus voltage to ≤19.1 V, preventing gate oxide stress on 25 V-rated power FETs without response-time delay.

Precision Bias Network for Op-Amp Circuits

Reference Voltage Source for ADC Drivers

Use Scenario: Supplies stable bias to input stage of rail-to-rail op-amp in 16-bit sensor signal conditioning module.

IC Role / Device Role / Timing Role: Provides fixed 18 V reference for dual-supply op-amp biasing network requiring low-drift, low-noise DC source.

Use Value: Delivers <5 ppm/°C effective tempco via series resistor compensation, enabling <0.01% gain drift over -40°C to +85°C.

Use Scenario: Sets reference level for single-ended ADC driver stage in programmable logic controller analog input module.

IC Role / Device Role / Timing Role: Serves as low-cost, discrete alternative to integrated voltage reference IC in 12-bit SAR ADC front-end.

Use Value: Achieves 0.5 LSB INL contribution at 18 V reference point, meeting ±1 LSB total unadjusted error budget.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
1N4746A	Same 18 V nominal rating, but ±5% tolerance and 1.0 W rating in DO-41; Z_Z = 20 Ω @ 21 mA vs. BZX85C18's 15 Ω @ 20 mA	Slightly higher dynamic impedance reduces regulation precision under fast load transients	Select when legacy 1N47xx footprint compatibility is required and 5 Ω higher Z_Z is acceptable
MMBZ5246B	SMT SOD-123 package, same 18 V/5%/500 mW rating; Z_Z = 23 Ω @ 10 mA; max T_J = 150°C vs. BZX85C18's 200°C	Lower power rating and reduced temperature capability limit use in high-ambient or high-power dissipation roles	Choose for space-constrained PCB layouts where through-hole mounting is not feasible

Compared with 1N4746A and MMBZ5246B, the BZX85C18 offers superior thermal robustness (200°C max) and lowest Zener impedance in its class, making it optimal for high-reliability linear regulation and clamping where stability under thermal stress is critical.

Availability

BZX85C18 is available at Aetrix Electronics and suitable for switch-mode power supply feedback, overvoltage protection clamp, and precision bias network applications requiring stable component supply and long-term obsolescence management.

Supply support for BZX85C18 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BZX85C18 belongs to the BZX85C series of general-purpose Zener diodes engineered for cost-effective, reliable voltage regulation and reference functions in high-volume industrial and consumer power systems.

FAQ

What is the nominal Zener voltage of the BZX85C18 and how is it tested?

The BZX85C18 has a nominal Zener voltage of 18 V, with a guaranteed range of 16.8 V to 19.1 V at I_Z = 20 mA and lead temperature T_L = 30°C ±1°C. This value is measured under thermal equilibrium conditions using standardized 3/8" lead length and controlled ambient, per onsemi's BZX85C3V3–BZX85C56 datasheet Rev. 2 (October 2017). The BZX85C18 maintains this specification across its full operating temperature range.

Does the BZX85C18 have a specified forward voltage?

Yes, the BZX85C18 has a maximum forward voltage (V_F) of 1.2 V at forward current I_F = 200 mA, as documented in the "Electrical Characteristics" section of the official onsemi datasheet. This parameter applies only during forward conduction mode and is relevant for polarity-check or surge-current path analysis-not for Zener regulation operation, which occurs in reverse bias.

What is the Zener impedance of the BZX85C18 and why does it matter?

The BZX85C18 exhibits a Zener impedance (Z_Z) of 15 Ω at I_Z = 20 mA. This low dynamic resistance directly determines how tightly the device regulates voltage under varying load currents-e.g., a ±5 mA change in Zener current causes only ±75 mV output shift. For the BZX85C18, this enables stable reference performance in feedback and clamping circuits where load transients occur.

Can the BZX85C18 be used in high-temperature environments?

Yes, the BZX85C18 is rated for operation from -65°C to +200°C, making it suitable for under-hood automotive, industrial furnace controls, and downhole equipment. Its glass DO-41 package retains mechanical integrity and electrical stability at elevated temperatures where plastic-packaged alternatives may degrade. Derating begins at 50°C (6.67 mW/°C), so at 125°C ambient, the BZX85C18 supports up to ~530 mW continuous dissipation.

How does the BZX85C18 compare to the BZX85C15 in terms of power handling and thermal behavior?

The BZX85C18 and BZX85C15 share identical absolute maximum ratings: both deliver 1.0 W at 25°C ambient and derate at 6.67 mW/°C above 50°C. Their thermal behavior is equivalent because they use the same DO-41 glass package and silicon process. However, the BZX85C18's higher Zener voltage results in greater power dissipation at the same current-e.g., 20 mA yields 360 mW in the BZX85C18 versus 300 mW in the BZX85C15-so thermal design must account for that difference.

BZX85C18 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: DO-204AL, DO-41, Axial

Packaging:: Bulk

Product Status:: Obsolete

Voltage - Zener (Nom) (Vz):: 18 V

Tolerance:: ±6%

Power - Max:: 1 W

Impedance (Max) (Zzt):: 20 Ohms

Current - Reverse Leakage @ Vr:: 500 nA @ 12.5 V

Voltage - Forward (Vf) (Max) @ If:: 1.2 V @ 200 mA

Operating Temperature:: -65°C ~ 200°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: DO-41

BZX85C18 FAQ

1.How can I place an order for BZX85C18 through Aetrix?

Please submit a Request for Quotation (RFQ) for BZX85C18 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 BZX85C18 reliable?

The price and inventory of BZX85C18 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BZX85C18 is usually 5 days.

3.What payment methods are accepted for BZX85C18?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BZX85C18 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BZX85C18?

BZX85C18 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BZX85C18 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 BZX85C18?

For technical support, including BZX85C18 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BZX85C18 requirements.

6.How does Aetrix verify that BZX85C18 is sourced from the original manufacturer or authorized distributors?

All BZX85C18 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 BZX85C18 meets industry standards.

7.What is the process for return or replacement of BZX85C18?

All BZX85C18 units undergo pre-shipment inspection (PSI). If there is an issue with BZX85C18, 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 BZX85C18 part is unused and in its original packaging.

Return procedure for BZX85C18:

1.Submit a request within 90 days.

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

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