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BZX85C18 Zener Diode 18V 1W Equivalent & Substitute Parts
Part Overview
The BZX85C18 is an 18 V, 1 W Zener diode manufactured by onsemi in DO-204AL (DO-41) axial through-hole packaging. This component is classified as obsolete, though 798 pieces remain in stock as new original inventory. The BZX85C18 is ROHS3 compliant and operates across a temperature range of -65°C to 200°C with a nominal Zener voltage tolerance of ±6%.
Due to the obsolete product status, equivalent and substitute Zener diodes with matching or superior electrical characteristics are necessary for new designs, production continuity, and long-term component availability. Substitute parts maintain the 18 V nominal Zener voltage while offering active product status, improved availability, and in many cases, enhanced compliance certifications.
Substiute Parts
Key Parameters
| Parameter | BZX85C18 | Unit |
|---|---|---|
| Voltage - Zener (Nom) | 18 | V |
| Tolerance | ±6% | % |
| Power - Max | 1 | W |
| Impedance (Max) | 20 | Ohms |
| Current - Reverse Leakage @ Vr | 500 nA @ 12.5 V | nA |
| Voltage - Forward (Vf) (Max) @ If | 1.2 V @ 200 mA | V |
| Operating Temperature | -65°C ~ 200°C | °C |
| Mounting Type | Through Hole | — |
| Package / Case | DO-204AL, DO-41, Axial | — |
| RoHS Status | ROHS3 Compliant | — |
Substitute Part Grouping Explanation
Substitution of the BZX85C18 is determined by the following critical parameters:
Primary Matching Criteria:
- Voltage - Zener (Nom): 18 V (exact match required)
- Mounting Type: Through Hole (axial configuration)
- Package / Case: DO-204AL, DO-41, or equivalent axial package
Secondary Compatibility Criteria:
- Power - Max: Equal to or greater than 1 W
- Impedance (Max): 20 Ohms or lower
- Operating Temperature Range: Must encompass or exceed -65°C to 200°C, or be suitable for the application's thermal requirements
- Tolerance: ±6% or tighter (±5%, ±2%)
Substitute parts are grouped into three categories:
- Direct Parametric Equivalents – Parts matching all primary criteria with identical or superior power ratings and impedance specifications
- Similar Functional Substitutes – Parts with 18 V nominal Zener voltage and through-hole axial mounting, with variations in power rating, impedance, or temperature range
- Active Product Alternatives – Parts with active product status offering improved long-term availability and compliance certifications
Parameter Comparison
| Manufacturer Part Number | Manufacturer | Voltage - Zener (Nom) | Tolerance | Power - Max | Impedance (Max) | Operating Temperature | Package / Case | Product Status | RoHS Status |
|---|---|---|---|---|---|---|---|---|---|
| BZX85C18 | onsemi | 18 V | ±6% | 1 W | 20 Ohms | -65°C ~ 200°C | DO-204AL, DO-41 | Obsolete | ROHS3 Compliant |
| 1N4746A | Microchip Technology | 18 V | ±5% | 1 W | 20 Ohms | -65°C ~ 200°C | DO-204AL, DO-41 | Active | RoHS non-compliant |
| BZX85C18-TAP | Vishay General Semiconductor - Diodes Division | 18 V | ±5% | 1.3 W | 20 Ohms | -55°C ~ 175°C | DO-204AL, DO-41 | Active | ROHS3 Compliant |
| 1N4746CE3/TR13 | Microchip Technology | 18 V | ±2% | 1 W | 20 Ohms | -65°C ~ 150°C | DO-204AL, DO-41 | Active | ROHS3 Compliant |
| 1N4746CP/TR12 | Microchip Technology | 18 V | ±2% | 1 W | 20 Ohms | -65°C ~ 150°C | DO-204AL, DO-41 | Active | RoHS non-compliant |
| 1N4746CP/TR8 | Microchip Technology | 18 V | ±2% | 1 W | 20 Ohms | -65°C ~ 150°C | DO-204AL, DO-41 | Active | RoHS non-compliant |
| 1N4746AP/TR12 | Microchip Technology | 18 V | ±5% | 1 W | 20 Ohms | -65°C ~ 150°C | DO-204AL, DO-41 | Active | RoHS non-compliant |
| 1N3026B-1 | Microchip Technology | 18 V | ±5% | 1 W | 20 Ohms | -55°C ~ 175°C | DO-204AL, DO-41 | Active | RoHS non-compliant |
| 1EZ18D5-TP | Micro Commercial Co | 18 V | ±5% | 1 W | 20 Ohms | -55°C ~ 150°C | DO-204AL, DO-41 | Active | Not specified |
| 1N5931BRLG | onsemi | 18 V | ±5% | 3 W | 12 Ohms | -65°C ~ 200°C | DO-204AL, DO-41 | Active | ROHS3 Compliant |
| 1N5248B | Microchip Technology | 18 V | ±5% | 500 mW | 21 Ohms | -65°C ~ 175°C | DO-204AH, DO-35 | Active | RoHS non-compliant |
Engineering Selection Recommendations
For Direct Replacement (Identical Electrical Performance):
The 1N4746A manufactured by Microchip Technology provides direct parametric equivalence to the BZX85C18. Both components feature 18 V nominal Zener voltage, ±5% tolerance (tighter than the original ±6%), 1 W maximum power dissipation, 20 Ohms maximum impedance, and identical DO-204AL (DO-41) axial through-hole packaging. The 1N4746A operates across -65°C to 200°C, matching the original temperature range. This part is in active product status with 50,200 pieces in stock. RoHS compliance status differs (non-compliant vs. ROHS3 compliant for the original); compliance requirements must be evaluated against application specifications.
For Enhanced Thermal Performance and Compliance:
The BZX85C18-TAP manufactured by Vishay General Semiconductor - Diodes Division is an active product offering superior power dissipation (1.3 W vs. 1 W), identical impedance (20 Ohms), and ROHS3 compliance matching the original. This part operates across -55°C to 175°C, which is narrower than the original range but suitable for most industrial and commercial applications. The BZX85C18-TAP carries AEC-Q101 automotive qualification and is available in cut tape packaging with 5,126 pieces in stock.
For Extended Temperature Range and Improved Availability:
The 1N5931BRLG manufactured by onsemi provides the widest operating temperature range (-65°C to 200°C, matching the original), ROHS3 compliance, and significantly enhanced power dissipation (3 W vs. 1 W). This part features lower impedance (12 Ohms vs. 20 Ohms), resulting in improved voltage regulation characteristics. The 1N5931BRLG is in active product status with 6,750 pieces in stock and is suitable for applications requiring higher power handling or tighter voltage regulation.
For Tighter Voltage Tolerance:
The 1N4746CE3/TR13 and 1N4746CP/TR12 manufactured by Microchip Technology offer ±2% Zener voltage tolerance (compared to ±6% for the original), providing superior voltage regulation accuracy. Both parts maintain 1 W power dissipation, 20 Ohms impedance, and DO-204AL (DO-41) packaging. The 1N4746CE3/TR13 is ROHS3 compliant with 709 pieces in stock; the 1N4746CP/TR12 is RoHS non-compliant with 948 pieces in stock. Operating temperature range is -65°C to 150°C for both variants.
For Lower Power Applications:
The 1N5248B manufactured by Microchip Technology is suitable for applications with reduced power requirements (500 mW vs. 1 W). This part features 18 V nominal Zener voltage, ±5% tolerance, and operates across -65°C to 175°C. The package differs (DO-204AH, DO-35 vs. DO-204AL, DO-41), requiring physical layout verification. With 62,638 pieces in stock, this part offers exceptional availability for lower-power circuit designs.
Frequently Asked Questions (FAQ)
Q: Can the 1N4746A directly replace the BZX85C18 in existing designs?
A: Yes. The 1N4746A matches all critical electrical parameters: 18 V nominal Zener voltage, 1 W maximum power dissipation, 20 Ohms maximum impedance, and identical DO-204AL (DO-41) axial through-hole packaging. The operating temperature range (-65°C to 200°C) is identical. The primary difference is RoHS compliance status; the 1N4746A is RoHS non-compliant while the original BZX85C18 is ROHS3 compliant. Compliance requirements must be verified against application and regulatory specifications.
Q: What is the difference between the BZX85C18-TAP and the original BZX85C18?
A: The BZX85C18-TAP is an active product variant manufactured by Vishay with enhanced power dissipation (1.3 W vs. 1 W), identical impedance (20 Ohms), and ROHS3 compliance. The operating temperature range is narrower (-55°C to 175°C vs. -65°C to 200°C). The BZX85C18-TAP carries AEC-Q101 automotive qualification and is supplied in cut tape packaging. For applications within the -55°C to 175°C range, this part offers improved availability and compliance certifications.
Q: Why would I select the 1N5931BRLG over the 1N4746A?
A: The 1N5931BRLG offers three key advantages: (1) significantly higher power dissipation (3 W vs. 1 W), enabling use in higher-power circuit designs; (2) lower impedance (12 Ohms vs. 20 Ohms), providing tighter voltage regulation; (3) identical operating temperature range (-65°C to 200°C) and ROHS3 compliance as the original. Select the 1N5931BRLG when circuit power requirements exceed 1 W or when improved voltage regulation is required.
Q: Are the 1N4746CE3/TR13 and 1N4746CP/TR12 interchangeable?
A: Both parts feature identical electrical specifications: 18 V nominal Zener voltage, ±2% tolerance, 1 W power dissipation, 20 Ohms impedance, and DO-204AL (DO-41) packaging. The primary difference is RoHS compliance: the 1N4746CE3/TR13 is ROHS3 compliant while the 1N4746CP/TR12 is RoHS non-compliant. Both operate across -65°C to 150°C. Selection depends on compliance requirements and available inventory.
Q: Can I use the 1N5248B as a substitute for the BZX85C18?
A: The 1N5248B is suitable only for applications with reduced power requirements. This part features 18 V nominal Zener voltage and ±5% tolerance, matching the original. However, power dissipation is 500 mW (half the original 1 W), and the package differs (DO-204AH, DO-35 vs. DO-204AL, DO-41). Physical layout verification is required. Use the 1N5248B only when circuit power requirements do not exceed 500 mW and the smaller package is physically compatible.
Q: What does the ±6% tolerance on the BZX85C18 mean compared to ±5% or ±2% alternatives?
A: Zener voltage tolerance specifies the acceptable deviation from the nominal 18 V specification. The BZX85C18 with ±6% tolerance allows Zener voltage between 16.92 V and 19.08 V. Alternatives with ±5% tolerance allow 17.1 V to 18.9 V, and ±2% alternatives allow 17.64 V to 18.36 V. Tighter tolerance (lower percentage) provides more precise voltage regulation. Select based on circuit voltage regulation requirements.
Q: Are all substitute parts ROHS3 compliant?
A: No. Of the listed substitutes, only the BZX85C18-TAP, 1N5931BRLG, and 1N4746CE3/TR13 are ROHS3 compliant. The 1N4746A, 1N4746CP/TR12, 1N4746CP/TR8, 1N4746AP/TR12, 1N3026B-1, and 1N5248B are RoHS non-compliant. The 1EZ18D5-TP does not specify RoHS status. Compliance requirements must be verified against application specifications and regulatory requirements.
Q: What is the significance of the operating temperature range differences?
A: The BZX85C18 operates from -65°C to 200°C. Some substitutes offer narrower ranges (e.g., 1N4746A variants operate to 150°C maximum). Operating temperature range defines the thermal environment in which the component functions reliably. For applications requiring operation above 150°C or below -55°C, select substitutes with matching or extended temperature ranges. For standard industrial and commercial applications (-40°C to 85°C), most substitutes are suitable.
Q: What does impedance (Zzt) represent, and why is it important?
A: Impedance (Zzt) is the dynamic impedance of the Zener diode at the specified test current, typically measured at 1 mA. Lower impedance indicates better voltage regulation—the Zener voltage remains more stable as load current varies. The BZX85C18 and most substitutes feature 20 Ohms impedance. The 1N5931BRLG offers superior 12 Ohms impedance, providing tighter voltage regulation. Select lower impedance values for applications requiring precise voltage stability.
Q: Can I use a higher-power Zener diode (like the 1N5931BRLG at 3 W) in place of a 1 W part?
A: Yes. A higher-power Zener diode is a valid substitute provided all other electrical parameters match (voltage, tolerance, impedance, temperature range, package). The higher power rating provides additional thermal margin and reliability. However, circuit design must ensure that actual power dissipation does not exceed the original 1 W specification unless the circuit is redesigned to accommodate higher power. Higher-power parts are physically larger and may require layout modifications.
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