1N973B Zener Diode Equivalent & Substitute Parts

Part Overview

The 1N973B is a 33 V, 500 mW Zener diode manufactured by onsemi in a DO-35 through-hole axial package. This component is classified as obsolete, necessitating identification of active equivalent and substitute parts for ongoing design requirements and procurement needs. The 1N973B serves voltage regulation and protection applications requiring precise 33 V reference voltage with ±5% tolerance and 500 mW power dissipation capability.

Substiute Parts

1N973B

onsemiIn Stock: 9201N973B Datasheet

Current PartRFQ

1EZ33D5-TP

Micro Commercial CoIn Stock: 11291EZ33D5-TP Datasheet

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1N5078

Microchip TechnologyIn Stock: 8311N5078 Datasheet

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1N5937BP-TP

Micro Commercial CoIn Stock: 7481N5937BP-TP Datasheet

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1N973A

Microchip TechnologyIn Stock: 16711N973A Datasheet

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1N973B-1

Microchip TechnologyIn Stock: 11441N973B-1 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 1N973B is determined by the following critical parameters:

Primary Matching Criteria:

• Voltage - Zener (Nom): 33 V (exact match required)
• Tolerance: ±5% or tighter (±10% acceptable with design review)
• Mounting Type: Through Hole (required for mechanical compatibility)

Secondary Compatibility Factors:

• Power - Max: 500 mW minimum (higher ratings acceptable for derating applications)
• Impedance (Max): 58 Ohms or lower (lower impedance provides improved performance)
• Current - Reverse Leakage: 5 µA or lower (lower leakage acceptable)
• Operating Temperature Range: Must encompass application requirements

Package Considerations:

• DO-35 (DO-204AH) is the primary package form
• DO-41 (DO-204AL) and axial packages are mechanically compatible with PCB layout modifications
• All substitute parts maintain axial through-hole configuration

Four substitute parts meet the electrical and mechanical requirements for the 1N973B:

1. 1N973B-1 (Microchip Technology): Identical electrical specifications with improved leakage performance and active product status
2. 1N5937BP-TP (Micro Commercial Co): Higher power rating (1.5 W) with improved impedance characteristics
3. 1EZ33D5-TP (Micro Commercial Co): Higher power rating (1 W) with improved impedance characteristics
4. 1N5078 (Microchip Technology): Highest power rating (3 W) with superior impedance and leakage performance

Parameter Comparison

Engineering Selection Recommendations

Direct Replacement (Identical Specifications):

The 1N973B-1 (Microchip Technology) is the primary recommended substitute. This part maintains identical electrical specifications (33 V, ±5%, 500 mW, 58 Ohms impedance) and package form (DO-35). The 1N973B-1 offers active product status, improved reverse leakage performance (500 nA versus 5 µA), ROHS3 compliance, and extended availability. This part provides drop-in compatibility with existing PCB designs and schematics.

Higher Power Rating Substitutes (Design Derating):

For applications requiring enhanced thermal performance or higher current handling:

• 1N5937BP-TP (Micro Commercial Co): 1.5 W power rating with 33 Ohms impedance. Requires PCB layout modification due to DO-41 package form. ROHS3 compliant. Suitable for designs with thermal margin requirements.

• 1EZ33D5-TP (Micro Commercial Co): 1 W power rating with 45 Ohms impedance. Requires PCB layout modification due to DO-41 package form. Suitable for moderate power derating applications.

• 1N5078 (Microchip Technology): 3 W power rating with 21 Ohms impedance. Highest performance option with superior impedance characteristics and lowest reverse leakage (1 µA). Requires PCB layout modification due to axial package form. Suitable for high-reliability and high-power applications.

Compliance Considerations:

All substitute parts maintain REACH Unaffected status consistent with the original 1N973B. The 1N973B-1, 1N5937BP-TP, and 1N5078 are active products with current manufacturing support. Selection should prioritize active product status to ensure long-term availability and supply chain stability.

Temperature Range Limitations:

The 1N973B operates to 200°C maximum junction temperature. Substitute parts 1N5937BP-TP and 1EZ33D5-TP have reduced upper temperature limits (175°C and 150°C respectively). Applications requiring operation above 175°C must use 1N973B-1 or 1N5078.

Frequently Asked Questions (FAQ)

Q: Can the 1N973B-1 be used as a direct replacement for the 1N973B?

A: Yes. The 1N973B-1 maintains identical zener voltage (33 V), tolerance (±5%), power rating (500 mW), impedance (58 Ohms), and package form (DO-35). Both parts are through-hole axial components with identical PCB footprints. The 1N973B-1 is active and recommended for new designs.

Q: What is the difference between DO-35 and DO-41 packages?

A: DO-35 (DO-204AH) and DO-41 (DO-204AL) are both through-hole axial packages with different physical dimensions. DO-35 is smaller and is the original package for the 1N973B. DO-41 is larger. Substitution with DO-41 parts (1N5937BP-TP, 1EZ33D5-TP) requires PCB layout modification to accommodate the larger package footprint.

Q: Can I use a higher power-rated zener diode as a substitute?

A: Yes, provided the zener voltage (33 V) and tolerance (±5%) remain identical. Higher power ratings (1 W, 1.5 W, 3 W) are acceptable and provide thermal margin. However, circuit design must account for the different impedance characteristics. Lower impedance (21 Ohms for 1N5078 versus 58 Ohms for 1N973B) may affect voltage regulation performance in some applications.

Q: What is reverse leakage current and why does it matter?

A: Reverse leakage current is the small current flowing through the zener diode when reverse-biased below the zener voltage. Lower leakage improves circuit performance in high-impedance applications. The 1N973B-1 offers superior leakage performance (500 nA) compared to the original 1N973B (5 µA), providing improved circuit stability.

Q: Are all substitute parts RoHS compliant?

A: The 1N973B-1 and 1N5937BP-TP are ROHS3 compliant. The 1EZ33D5-TP and 1N5078 do not specify RoHS status in the provided data. All parts maintain REACH Unaffected status.

Q: What is the operating temperature range limitation?

A: The 1N973B operates from -65°C to 200°C. Substitute parts have the following limits: 1N973B-1 (-65 to 175°C), 1N5937BP-TP (-55 to 175°C), 1EZ33D5-TP (-55 to 150°C), and 1N5078 (-65 to 175°C). Applications requiring operation above 175°C must use the original 1N973B or verify alternative solutions.

Q: Which substitute part offers the best overall performance?

A: The 1N973B-1 is the optimal choice for direct replacement due to identical specifications, active product status, improved leakage performance, and ROHS3 compliance. For applications requiring higher power dissipation capability, the 1N5078 offers superior impedance (21 Ohms) and leakage characteristics (1 µA) with 3 W power rating.

Q: Can I mix different substitute parts in the same circuit?

A: Yes, provided all parts maintain the same zener voltage (33 V) and tolerance (±5%). However, mixing parts with different impedance values may affect voltage regulation uniformity across parallel branches. Circuit design should account for impedance variations when using multiple substitute parts.

Q: What inventory status should I consider for procurement?

A: All substitute parts are listed as in-stock with active product status. The 1N973B-1 has 1107 units available, 1N5078 has 767 units, 1N5937BP-TP has 724 units, and 1EZ33D5-TP has 1056 units. Active product status ensures continued availability and manufacturing support.