Microchip Technology 1N972B

Overview

1N972B from Microsemi is a silicon 500 mW axial-lead Zener diode with nominal Zener voltage 30 V, ±5% tolerance (B suffix), 49 Ω dynamic impedance at 4.2 mA test current, and +0.091 %/°C temperature coefficient. It operates across –65 °C to +175 °C and regulates voltage in low-power reference and protection circuits.

For engineers reviewing the 1N972B datasheet, 1N972B pinout, 1N972B application, or 1N972B equivalent, this device serves as a precision voltage clamp in analog power supplies, overvoltage protection stages, and calibration references where stable 30 V regulation under variable load and temperature is required.

Technical Context

The 1N972B functions as a reverse-biased voltage reference diode with sharp breakdown knee, verified by dual-point Zener impedance measurement per MicroNote 202. Its 30 V nominal Zener voltage is specified at 4.2 mA test current (IZT) with 750 Ω maximum impedance at knee current (IZK = 0.25 mA).

Thermal design relies on DO-35 package characteristics: 250 °C/W junction-to-lead thermal resistance at 10 mm lead length, derating to 400 mW max dissipation at 75 °C lead temperature. Polarity is marked by cathode band; operation requires banded end positive relative to anode.

Key Specifications

Pinout & Package

Package: DO-35 (DO-204AH), hermetically sealed glass axial-leaded case with tin-lead or RoHS-compliant matte-tin plating. Cathode indicated by single black band; diode operated with banded end positive.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N972B, the 1N4745A offers higher power margin but requires PCB layout revision due to DO-41 size, while BZX55C30 matches form, fit, and function for non-radiation-critical applications-making it a direct replacement where Microsemi's radiation hardness is not mandated.

Availability

1N972B is available at Aetrix Electronics and suitable for industrial power supplies, sensor interface protection circuits, and calibration equipment requiring stable component supply with long-term obsolescence management.

Supply support for 1N972B 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-voltage discrete components for aerospace, defense, and industrial markets.

The 1N972B belongs to Microsemi's legacy 1N957B–1N992B Zener series designed for precision voltage regulation in harsh-environment applications where stability, ESD immunity, and extended temperature operation are critical.

FAQ

What is the Zener voltage tolerance for 1N972B?

The 1N972B has a nominal Zener voltage of 30 V with ±5% tolerance, indicated by the "B" suffix per JEDEC standard. This means the actual measured VZ at 4.2 mA test current falls between 28.5 V and 31.5 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 +0.091 %/°C coefficient.

Can 1N972B be used in surface-mount designs?

No, the 1N972B is exclusively offered in the axial-leaded DO-35 (DO-204AH) through-hole package. Microsemi does not manufacture a surface-mount variant of the 1N972B. For SMT equivalents, consider the MLL972B (DO-213AA MELF) or BZX55C30 in SOD-123, but verify pin compatibility and thermal derating separately for each design.

What is the maximum power dissipation for 1N972B at 75 °C lead temperature?

The 1N972B is rated for 400 mW maximum steady-state power dissipation at a lead temperature (TL) of 75 °C, measured 10 mm from the body. At lower TL (e.g., 50 °C), it supports full 500 mW. Derating follows the 250 °C/W junction-to-lead thermal resistance curve shown in Figure 1 of the Microsemi datasheet.

How does the temperature coefficient affect 1N972B performance in a 0–70 °C ambient range?

With a +0.091 %/°C temperature coefficient, the 1N972B's Zener voltage increases by approximately 191 mV over a 70 °C rise (30 V × 0.00091 × 70). This drift is linear and predictable, enabling compensation in precision references. For example, at 70 °C, VZ ≈ 30.19 V versus 30.00 V at 25 °C-verified in Figure 2 of the Microsemi datasheet.

Is 1N972B RoHS compliant?

The base 1N972B is not RoHS compliant; RoHS compliance requires the "e3" suffix (i.e., 1N972Be3). The e3 version uses annealed matte-tin plating instead of tin-lead, meeting EU Directive 2011/65/EU. Both versions share identical electrical specifications and DO-35 packaging dimensions, differing only in terminal finish and compliance status.