Microchip Technology 1N4738AUR/TR

Overview

1N4738AUR/TR from Microsemi is a surface-mount 1.0 W glass-encapsulated Zener diode with nominal Zener voltage of 8.2 V, ±5% tolerance (A suffix), 4.5 Ω dynamic impedance at 31 mA test current, and maximum reverse leakage of 6 μA at 6.5 V. It operates from –65°C to +175°C and is used for precision voltage regulation in power supply feedback loops, reference circuits, and overvoltage protection.

For engineers reviewing the 1N4738AUR/TR datasheet, 1N4738AUR/TR pinout, 1N4738AUR/TR application, or 1N4738AUR/TR equivalent, key selection criteria include Zener voltage accuracy, thermal resistance (130°C/W on FR4), surge current rating (550 mA), hermetic glass MELF package reliability, and RoHS-compliant e3 plating.

Technical Context

This device implements a silicon planar Zener junction optimized for stable breakdown in the 8.2 V range. Its DO-213AB glass MELF package provides low parasitic capacitance (typ. 50 pF per Figure 2) and inherent radiation hardness per MicroNote 050. The cathode band marking and polarity-sensitive operation require the banded end to be held positive relative to the anode during regulation.

It delivers regulated output across a wide current range (IZK = 0.5 mA to IZM = 550 mA at TA = 50°C), with sharp knee impedance (ZZK = 400 Ω at IZK = 0.5 mA) ensuring stable turn-on. Thermal derating follows a linear curve: full 1.0 W up to 45°C ambient on FR4, then reduced to zero at 125°C end-cap temperature.

Key Specifications

Pinout & Package

Package: DO-213AB glass MELF (hermetically sealed, leadless cylindrical body, 2.39–2.66 mm diameter × 4.80–5.20 mm length). Cathode identified by single black band; anode is unmarked end. Requires reflow-compatible footprint per Microsemi recommended pad layout (1.8 mm pad width, 2.8 mm pad length, 7.0 mm center-to-center spacing).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N4738AUR/TR, the 1N4738A-T offers identical electrical specs but lacks surface-mount compatibility and thermal performance on FR4, while the BZX84-C8V2LT1G trades power handling and surge robustness for miniaturization-making 1N4738AUR/TR optimal for 1 W industrial regulation where reliability and thermal margin are critical.

Availability

1N4738AUR/TR is available at Aetrix Electronics and suitable for switch-mode power supplies, industrial sensor references, overvoltage clamp protection, and automotive ECU voltage monitoring requiring stable component supply and long-lifecycle support.

Supply support for 1N4738AUR/TR 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 1N47xxAUR series was designed specifically for surface-mount voltage regulation in mission-critical systems demanding hermetic sealing, radiation tolerance, and extended temperature operation.

FAQ

What is the Zener voltage tolerance of the 1N4738AUR/TR?

The 1N4738AUR/TR has a nominal Zener voltage of 8.2 V with a tolerance of ±5%, indicated by the "A" suffix in its part number. This tolerance is verified at 30°C with 90-second stabilization after DC current application, per Microsemi's test methodology. The 1N4738AUR/TR maintains this specification across its full operating temperature range of –65°C to +175°C, making it suitable for precision regulation where tighter tolerances than standard 10% parts are required.

How does the DO-213AB package of the 1N4738AUR/TR affect thermal performance?

The DO-213AB glass MELF package of the 1N4738AUR/TR yields a junction-to-ambient thermal resistance of 130°C/W when mounted on FR4 with 1 oz copper and Microsemi's recommended footprint. This is significantly higher than axial packages like DO-41 (65°C/W), meaning PCB layout must include adequate copper pour and thermal vias. The 1N4738AUR/TR delivers full 1.0 W only below 45°C ambient; above that, power must be linearly derated to prevent junction overheating.

Can the 1N4738AUR/TR replace axial 1N4738A diodes in existing designs?

No direct replacement is possible without layout revision: the 1N4738AUR/TR uses a DO-213AB surface-mount MELF package, whereas the 1N4738A uses a DO-41 axial-leaded package. Their footprints, soldering profiles, and thermal paths differ fundamentally. While electrically equivalent, substituting the 1N4738AUR/TR requires redesigning the PCB pad layout and requalifying thermal performance. The 1N4738AUR/TR is intended for new high-density SMT designs-not drop-in upgrades.

What is the maximum surge current rating for the 1N4738AUR/TR?

The 1N4738AUR/TR is rated for a maximum surge current (I_S) of 550 mA, measured using a ½ sine-wave pulse of 1/120 second duration at 25°C ambient. This rating enables the 1N4738AUR/TR to absorb short-duration overvoltage transients-such as those from relay coil collapse or ESD events-without parametric shift or failure. Sustained operation above 550 mA, even briefly, risks irreversible junction damage due to localized thermal runaway.

Is the 1N4738AUR/TR compliant with RoHS and other environmental standards?

Yes, the 1N4738AUR/TR carries the "e3" suffix, indicating RoHS-compliant matte-tin plating per JEDEC J-STD-609. It contains no lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE above threshold limits. The device also meets MIL-PRF-19500 screening requirements when ordered with appropriate prefixes (e.g., MV for JANTXV), and its hermetic glass construction avoids halogenated flame retardants common in plastic-packaged alternatives.