Microchip Technology 1N978B

Overview

1N978B from Microsemi is a silicon 500 mW axial-lead Zener diode in DO-35 (DO-204AH) package, rated for 51 V nominal Zener voltage at 2.5 mA test current, with ±5% tolerance (B suffix), 1500 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 control and instrumentation systems.

For engineers reviewing the 1N978B datasheet, 1N978B pinout, 1N978B application, or 1N978B equivalent, key selection criteria include its 51 V regulation point, 2.5 mA Zener test current, 1500 Ω dynamic impedance, -65°C to +175°C operating temperature range, and DO-35 glass axial-leaded mechanical form factor.

Technical Context

The 1N978B operates as a reverse-biased voltage reference diode, maintaining stable 51 V output across a regulated current range from 0.25 mA (IZK) to 7.4 mA (IZM), with minimal capacitance and inherent radiation hardness per MicroNote 050. Its Zener knee is verified via dual-point impedance measurement per JEDEC standards.

Thermal performance is defined by 250 °C/W junction-to-lead resistance at 3/8″ lead length and 310 °C/W junction-to-ambient on FR4 board; power derating begins above 50 °C lead temperature, limiting steady-state dissipation to 480 mW at TL < 50 °C and 400 mW at TL = 75 °C.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH), hermetically sealed axial-lead glass body with tin-lead or RoHS-compliant matte-tin plating; cathode indicated by band; polarity requires banded end to be positive during Zener operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N978B, 1N5234B offers marginally lower voltage but reduced regulation precision due to higher Z_ZT, while BZX55-C51 delivers superior impedance performance at the cost of missing military-grade bonding and radiation tolerance-making 1N978B optimal for high-reliability, extended-temperature, or radiation-exposed deployments.

Availability

1N978B is available at Aetrix Electronics and suitable for industrial voltage reference, overvoltage protection clamp, temperature-stable bias generator, and low-power sensor excitation applications requiring stable component supply and long-term obsolescence management.

Supply support for 1N978B 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 1N978B belongs to Microsemi's legacy 1N957B–1N992B Zener series, designed specifically for precision voltage regulation in harsh-environment applications where wide temperature range, ESD immunity, and radiation tolerance are critical.

FAQ

What is the nominal Zener voltage and tolerance of the 1N978B?

The 1N978B has a nominal Zener voltage of 51 V with a ±5% tolerance, as indicated by the "B" suffix per JEDEC standard. This means the actual measured Zener voltage at 2.5 mA test current falls between 48.45 V and 53.55 V at 25 °C, verified under controlled lead-temperature conditions per Microsemi's test methodology.

What is the maximum Zener test current and corresponding impedance for the 1N978B?

The 1N978B is characterized at a Zener test current (I_ZT) of 2.5 mA, with a maximum Zener impedance (Z_ZT) of 1500 Ω at that current. This impedance value reflects the dynamic resistance near the breakdown knee and directly impacts regulation accuracy under varying load conditions.

Does the 1N978B support RoHS compliance and what suffix indicates it?

Yes, the 1N978B supports RoHS compliance when ordered with the "e3" suffix (e.g., 1N978Be3). This version uses annealed matte-tin plating instead of tin-lead, meeting EU Directive 2011/65/EU without altering electrical specifications, thermal resistance, or mechanical dimensions.

What is the operating temperature range and thermal resistance specification for the 1N978B?

The 1N978B operates from -65 °C to +175 °C. Its thermal resistance is 250 °C/W junction-to-lead at 3/8″ (10 mm) lead length, and 310 °C/W junction-to-ambient on FR4 board with specified copper pad layout-enabling accurate thermal design for both lead-soldered and PCB-mounted configurations.

How does the temperature coefficient of the 1N978B affect its regulation stability?

The 1N978B has a positive temperature coefficient of +0.096 %/°C, meaning its Zener voltage increases predictably with rising junction temperature. This allows designers to compensate for thermal drift in precision references or select complementary components for zero-TC designs, especially in unregulated environments.