Microchip Technology 1N977A

Overview

1N977A from Microsemi is a silicon 500 mW axial-lead Zener diode with nominal Zener voltage 47 V, ±10% tolerance (A suffix), 2.7 mA Zener test current, 105 Ω dynamic impedance at I_ZT, and maximum reverse leakage of 5 μA at 35.8 V. It operates across –65 °C to +175 °C and is used for precision voltage reference and overvoltage protection in industrial power supplies.

For engineers reviewing the 1N977A datasheet, 1N977A pinout, 1N977A application, or 1N977A equivalent, key selection criteria include its DO-35 glass package, cathode-band polarity marking, thermal resistance of 250 °C/W (junction-to-lead), and JEDEC-registered 47 V regulation at 2.7 mA - critical for stable biasing and clamp design under wide temperature swings.

Technical Context

The 1N977A functions as a two-terminal voltage regulator diode operating in reverse breakdown, where Zener conduction maintains a stable 47 V reference across its terminals within ±10% tolerance. Its 105 Ω Zener impedance at 2.7 mA ensures predictable regulation slope, while its 5 μA reverse leakage at 35.8 V confirms low standby current draw in high-impedance sensing circuits.

Designed for axial-leaded through-hole mounting in the DO-35 (DO-204AH) package, the 1N977A features hermetically sealed glass construction, tin-lead or RoHS-compliant matte-tin plating, and inherent radiation hardness per MicroNote 050. It is rated for 0.5 W steady-state dissipation at lead temperature <50 °C and derates linearly above that point.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH), hermetically sealed axial-lead glass case with cathode indicated by colored band. 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 voltage regulation applications.

Compared with 1N977B and 1N5278B, the 1N977A provides the lowest-cost option for 47 V clamping where ±10% tolerance is acceptable, retains full DO-35 mechanical compatibility, and delivers superior low-current performance due to its 2.7 mA I_ZT - minimizing quiescent power in battery-backed systems.

Availability

1N977A is available at Aetrix Electronics and suitable for industrial power supplies, overvoltage protection circuits, high-temperature sensor biasing, and legacy analog instrumentation requiring stable component supply and long-lifecycle support.

Supply support for 1N977A 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 1N977A belongs to Microsemi's legacy 1N957B–1N992B Zener series, designed specifically for ruggedized voltage regulation in harsh-environment applications where extended temperature range and hermetic packaging are mandatory.

FAQ

What is the Zener voltage tolerance of the 1N977A?

The 1N977A has a nominal Zener voltage of 47 V with a ±10% tolerance, as indicated by the "A" suffix per Microsemi's documentation. This means the actual measured Zener voltage at 2.7 mA will fall between 42.3 V and 51.7 V at 25 °C. The tolerance is wider than the ±5% offered by the 1N977B variant, making the 1N977A appropriate for non-critical regulation tasks where cost optimization is prioritized over precision.

What is the maximum power dissipation rating for the 1N977A?

The 1N977A is rated for 500 mW steady-state power dissipation when the lead temperature (T_L) is maintained at or below 50 °C, measured 3/8 inch from the body. Above 50 °C, power must be linearly derated at 5.0 mW/°C, reaching zero dissipation at 150 °C lead temperature. This derating curve is defined in Figure 1 of the official Microsemi datasheet for the 1N957B–1N992B series.

Does the 1N977A have RoHS-compliant packaging options?

Yes - RoHS-compliant versions of the 1N977A are available by adding the "e3" suffix (e.g., 1N977Ae3), indicating annealed matte-tin plating per JEDEC standards. The base 1N977A uses traditional tin-lead plating, but both variants share identical electrical specifications, DO-35 package dimensions, and thermal characteristics. Customers selecting the e3 version must verify compatibility with their soldering process profile.

What is the reverse leakage current specification for the 1N977A?

The 1N977A specifies a maximum reverse leakage current (I_R) of 5 μA at a reverse voltage (V_R) of 35.8 V, measured at 25 °C. This value reflects the diode's ability to block current below its Zener knee, ensuring minimal loading in high-impedance reference networks. Leakage remains well below 10 μA across the full –65 °C to +125 °C operating range per characterization data in the Microsemi datasheet.

How is polarity marked on the 1N977A DO-35 package?

The 1N977A uses a cathode-band marking convention: a single colored band (typically black or dark gray) encircles the glass body near one end, identifying the cathode terminal. During Zener operation, the banded end must be held positive relative to the unmarked (anode) end. This polarity is consistent across all DO-35 Zeners in the 1N957B–1N992B family and is verified in the mechanical drawings on page 3 of the Microsemi datasheet.