Microchip Technology 1N979B

Overview

1N979B from Microsemi is a silicon 500 mW axial-leaded Zener diode in DO-35 (DO-204AH) package, rated for 56 V nominal Zener voltage at 2.2 mA test current, with ±5% tolerance (B suffix), 2000 Ω maximum Zener impedance at I_ZT, and +0.096 %/°C temperature coefficient. It regulates voltage in low-power reference and protection circuits across industrial temperature range.

For engineers reviewing the 1N979B datasheet, 1N979B pinout, 1N979B application, or 1N979B equivalent, key selection factors include its 56 V regulation precision, 2.2 mA minimum stable Zener current, 6.8 mA maximum DC Zener current, 35 mA surge capability, and DO-35 mechanical compatibility with through-hole PCB layouts.

Technical Context

The 1N979B operates as a reverse-biased voltage reference diode, maintaining stable 56 V output over a broad current range (2.2–6.8 mA) and temperature (-65°C to +175°C). Its Zener impedance of 2000 Ω at 2.2 mA and +0.096 %/°C temperature coefficient define regulation stability under thermal and load variation.

Designed for axial-leaded mounting, it features hermetically sealed glass DO-35 construction, tin-lead or RoHS-compliant matte-tin plating, cathode band polarity marking, and 0.2 g mass. It meets JEDEC registration requirements and exhibits ESD immunity per MIL-STD-750 Method 1020.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH), hermetically sealed axial-leaded glass body, 0.2 g mass, cathode indicated by colored band.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N979B, 1N5255B offers significantly lower Zener impedance for improved load regulation but reduced thermal margin at high lead temperatures, while BZX55-C56 provides better impedance performance at higher test current but requires stricter ambient thermal management.

Availability

1N979B is available at Aetrix Electronics and suitable for voltage reference design, overvoltage protection circuits, analog signal conditioning, and calibration standards requiring stable component supply and long-lifecycle support.

Supply support for 1N979B 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, RF, and radiation-hardened components for aerospace, defense, and industrial markets.

The 1N957B–1N992B series was engineered for ruggedized, through-hole Zener regulation in mission-critical systems where hermetic sealing, wide temperature operation, and JEDEC-standard compliance are mandatory.

FAQ

What is the Zener voltage tolerance for 1N979B?

The 1N979B has a nominal Zener voltage of 56 V with a ±5% tolerance, as indicated by the "B" suffix per JEDEC standard. This means the actual measured Zener voltage at 2.2 mA test current falls between 53.2 V and 58.8 V at 25°C. The tolerance remains valid across the full operating temperature range of −65°C to +175°C, though voltage drift follows the +0.096 %/°C coefficient.

Can 1N979B be used in surface-mount designs?

No, the 1N979B is exclusively a through-hole DO-35 axial-leaded device and is not surface-mount compatible. For SMT equivalents, Microsemi offers the MLL979B in DO-213AA (MELF) package, which shares identical electrical specifications including 56 V ±5% Zener voltage and +0.096 %/°C temperature coefficient.

What is the maximum power dissipation for 1N979B at 75°C lead temperature?

At a lead temperature (T_L) of 75°C measured 3/8 inch from the body, the 1N979B is rated for 400 mW steady-state power dissipation. This derating from the 500 mW rating at T_L < 50°C reflects thermal limits defined in Microsemi's datasheet Note 4 and ensures reliable long-term operation without junction overheating.

Does 1N979B require heatsinking in typical PCB layouts?

No, the 1N979B does not require external heatsinking in standard FR4 PCB layouts with 1 oz copper, 4 mm² pads, and 1 mm track width. Its thermal resistance is 310°C/W junction-to-ambient under those conditions, and its 400 mW max dissipation at 75°C lead temperature is achievable with natural convection cooling alone in most industrial enclosures.

How is polarity identified on the 1N979B package?

The cathode of the 1N979B is marked by a visible color band on the glass DO-35 body; the banded end must be connected to the higher-potential node for proper Zener regulation. During forward conduction, the anode (non-banded end) connects to the more positive potential, with forward voltage ≤1.3 V at 200 mA per datasheet specification.