Microchip Technology 1N979A

Overview

1N979A from Microsemi is a silicon 500 mW axial-lead Zener diode with nominal Zener voltage 56 V, ±10% tolerance (A suffix), 2.2 mA Zener test current, 2000 Ω maximum Zener impedance at I_ZT, 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 1N979A datasheet, 1N979A pinout, 1N979A application, or 1N979A equivalent, key selection criteria include its 56 V nominal regulation, DO-35 glass package thermal limits (250 °C/W junction-to-lead), 5 μA max reverse leakage at 42.6 V, and compatibility with manual or wave soldering per MIL-STD-750.

Technical Context

The 1N979A operates as a two-terminal voltage reference device, conducting in reverse breakdown to maintain a stable 56 V across its terminals over a defined current range (IZK = 0.25 mA to IZM = 6.8 mA). Its Zener knee is characterized by 2000 Ω dynamic impedance at 2.2 mA test current and exhibits +0.096 %/°C temperature coefficient.

Designed for through-hole mounting in DO-35 (DO-204AH) glass axial-leaded package, it features tin-lead or RoHS-compliant matte-tin plating, cathode band marking, and hermetic sealing. Thermal performance is specified at 3/8″ lead length (250 °C/W) and on FR4 board (310 °C/W), supporting operation up to 175 °C junction temperature.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH) - hermetically sealed axial-lead glass case with cathode band marking; terminals are tin-lead or RoHS-compliant matte-tin plated, solderable per MIL-STD-750 Method 2026.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N979A, the 1N979B offers tighter voltage tolerance for precision references, while the MMBZ5255B enables miniaturization and SMT manufacturing-neither is pin-compatible, but both serve overlapping regulation roles in different form factors and accuracy tiers.

Availability

1N979A is available at Aetrix Electronics and suitable for overvoltage clamping, low-power voltage referencing, and legacy power supply feedback requiring stable component supply and long-lifecycle support.

Supply support for 1N979A 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 analog and mixed-signal components for aerospace, defense, and industrial markets.

The 1N957B–1N992B series was designed for ruggedized, through-hole Zener regulation in mission-critical systems where hermetic packaging, wide temperature operation, and JEDEC standardization are essential.

FAQ

What is the nominal Zener voltage and tolerance of the 1N979A?

The 1N979A has a nominal Zener voltage of 56 V with ±10% tolerance, indicated by the "A" suffix per JEDEC standard. This means the actual breakdown voltage falls between 50.4 V and 61.6 V at 2.2 mA test current and 25 °C ambient, making it suitable for applications where moderate regulation accuracy is acceptable.

What package type does the 1N979A use and what are its key mechanical features?

The 1N979A uses the DO-35 (DO-204AH) axial-lead glass package: hermetically sealed, with cathode identified by a band, tin-lead or RoHS-compliant matte-tin plating, and weight of 0.2 g. Its dimensions comply with JEDEC standards, enabling compatibility with standard axial-lead insertion equipment and wave soldering profiles up to 260 °C for 10 seconds.

What is the maximum steady-state power dissipation for the 1N979A and how does it derate with temperature?

The 1N979A is rated for 500 mW at lead temperature < 50 °C (measured 3/8″ from body); power must be derated linearly above that point at 4 mW/°C, reaching zero at 175 °C. On FR4 board with 4 mm² copper pads, its thermal resistance rises to 310 °C/W, limiting usable power to ~480 mW at 25 °C ambient.

How does the 1N979A perform under reverse bias below its Zener voltage?

Below 42.6 V (75% of nominal 56 V), the 1N979A exhibits ≤5 μA reverse leakage current at 25 °C. This low leakage supports high-impedance bias networks and minimizes error current in reference circuits, preserving accuracy without requiring additional current-limiting resistors beyond those needed for Zener biasing.

Is the 1N979A suitable for high-reliability or extended-temperature applications?

Yes-the 1N979A is rated for −65 °C to +175 °C operating and storage temperature, meets MIL-STD-750 ESD testing (Method 1020), and features hermetic glass construction. These attributes make it appropriate for automotive under-hood modules, downhole oilfield electronics, and industrial control systems demanding long-term stability without conformal coating.