Microchip Technology 1N973A

Overview

1N973A from Microsemi is a silicon 500 mW axial-lead Zener diode with nominal Zener voltage 33 V, ±10% tolerance (A suffix), 3.8 mA Zener test current (IZT), 1000 Ω maximum Zener impedance at IZT, and −65 °C to +175 °C operating temperature range. It regulates voltage in low-power reference and protection circuits where stable breakdown under reverse bias is required.

For engineers reviewing the 1N973A datasheet, 1N973A pinout, 1N973A application, or 1N973A equivalent, key selection criteria include its 33 V nominal regulation, DO-35 glass package thermal resistance (250 °C/W junction-to-lead), 5 μA max reverse leakage at 25.1 V, and suitability for industrial power supply feedback, overvoltage clamping, and precision voltage reference designs.

Technical Context

The 1N973A operates as a two-terminal voltage reference device, conducting in reverse breakdown when cathode voltage exceeds anode by ≥33 V. Its Zener mechanism dominates in the 33 V range, delivering predictable regulation across 1–12 mA operating current with minimal temperature-induced drift (αVZ = +0.092 %/°C).

It features a hermetically sealed DO-35 (DO-204AH) glass axial-leaded package with tin-lead plating, cathode band marking, and mechanical robustness validated per MIL-STD-750. Thermal performance is specified at 3/8″ lead length (250 °C/W) and on FR4 board (310 °C/W), supporting reliable operation in high-reliability embedded systems.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH) - hermetically sealed glass axial-leaded case with cathode indicated by colored band; terminals are unmarked anode and banded cathode.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N973B and MMBZ5255BLT1G, the 1N973A offers the highest continuous power handling (500 mW) in a through-hole DO-35 package with ±10% tolerance-ideal for ruggedized, serviceable, or high-temperature analog subsystems where precision is secondary to reliability and thermal margin.

Availability

1N973A is available at Aetrix Electronics and suitable for industrial power supplies, overvoltage protection circuits, and high-temperature embedded monitoring systems requiring stable component supply and long-term obsolescence management.

Supply support for 1N973A 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

Microsemi (now part of Microchip Technology) is a U.S.-based semiconductor company specializing in high-reliability, radiation-hardened, and high-temperature analog components for aerospace, defense, and industrial markets.

The 1N957B–1N992B Zener series was designed for mission-critical voltage regulation where long-term stability, wide temperature operation, and JEDEC-standard interchangeability are essential-particularly in legacy and safety-certified systems.

FAQ

What is the Zener voltage tolerance of the 1N973A?

The 1N973A has a nominal Zener voltage of 33 V with ±10% tolerance, as indicated by the "A" suffix per Microsemi's documentation. This means the actual breakdown voltage falls between 29.7 V and 36.3 V at 25 °C and 3.8 mA test current. The tolerance is wider than the ±5% "B" variant but provides cost and availability advantages for non-critical regulation tasks.

Does the 1N973A require heatsinking in standard PCB mounting?

No, the 1N973A does not require external heatsinking under typical conditions. Its 500 mW power rating applies at lead temperature < 50 °C with 3/8″ lead length, and it achieves 310 °C/W thermal resistance on FR4 board with 4 mm² copper pads. At ≤250 mW dissipation and ambient ≤70 °C, self-heating remains within safe limits without added thermal mass.

Is the 1N973A RoHS compliant?

The base 1N973A is not RoHS compliant by default. RoHS-compliant versions are available with the "e3" suffix (e.g., 1N973Ae3), featuring annealed matte-tin plating instead of tin-lead. Always verify the full part number suffix when ordering for lead-free assembly; the "e3" designation is mandatory for RoHS conformance.

What is the maximum reverse leakage current for the 1N973A?

The 1N973A specifies a maximum reverse leakage current (IR) of 5 μA at VR = 25.1 V (76% of nominal 33 V). This low leakage ensures minimal standby power draw in voltage reference or clamping applications and contributes to stable regulation at light loads without significant error contribution.

Can the 1N973A be used in place of the 1N973B?

Yes, the 1N973A can substitute for the 1N973B in applications tolerant of ±10% Zener voltage variation instead of ±5%. Both share identical DO-35 packaging, thermal ratings, Zener impedance, and temperature coefficient. However, avoid substitution in precision feedback paths where tighter voltage accuracy is required-confirm system-level tolerance margins before replacement.