Microchip Technology 1N5255B

Overview

1N5255B from Microsemi is a 500 mW, 28 V ±5% glass axial-lead Zener diode in DO-35 (DO-204AH) package, designed for precision voltage regulation and reference applications in low-power analog circuits, power supply feedback paths, and overvoltage protection. It delivers 28 V nominal Zener voltage at 44 mA test current, with 600 Ω maximum Zener impedance at knee current and ±0.091 %/°C temperature coefficient.

For engineers reviewing the 1N5255B datasheet, 1N5255B pinout, 1N5255B application, or 1N5255B equivalent, key selection criteria include its 28 V regulation accuracy, 500 mW power rating at 25°C, DO-35 mechanical compatibility, low 0.1 μA max reverse leakage at 22.4 V, and suitability for industrial temperature range (-65°C to +175°C) operation.

Technical Context

The 1N5255B operates as a two-terminal voltage reference device relying on controlled reverse-biased avalanche breakdown. Its Zener voltage is stabilized by heavy doping and optimized junction geometry, enabling predictable regulation across 0.25 mA to 44 mA operating current range.

Thermal resistance is specified at 250 °C/W junction-to-lead (3/8" lead length) and 310 °C/W junction-to-ambient on FR4 board, directly governing derating above 25°C. The cathode band identifies polarity, requiring the banded end to be held positive relative to the anode for regulation.

Key Specifications

Pinout & Package

DO-35 (DO-204AH) hermetically sealed glass axial-leaded package with tin-lead or RoHS-compliant matte-tin plating; cathode identified by single black band; weight 0.2 g.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N5255B, 1N4749A offers higher power margin but sacrifices low-current stability and DO-35 form factor, while BZX55C27 provides better Zener impedance and RoHS compliance but lacks radiation hardness and military screening support.

Availability

1N5255B is available at Aetrix Electronics and suitable for industrial power supply feedback, overvoltage protection clamping, and precision analog reference applications requiring stable component supply, long-term lifecycle continuity, and traceable sourcing.

Supply support for 1N5255B 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 aerospace-grade analog and mixed-signal components.

The 1N52xxB series belongs to Microsemi's legacy DO-35 Zener diode product line, engineered for demanding applications including military, space, and extended-temperature industrial systems where stability, hermeticity, and radiation tolerance are mandatory.

FAQ

What is the nominal Zener voltage and tolerance of the 1N5255B?

The 1N5255B has a nominal Zener voltage of 28 V with a guaranteed tolerance of ±5%, as indicated by the "B" suffix per JEDEC specification. This means the actual measured V_Z falls between 26.6 V and 29.4 V when tested at 44 mA under standard conditions (25°C, 3/8" lead length). The 1N5255B is not rated for tighter tolerances like ±1% or ±2% - those require C or D suffix variants.

What is the maximum power dissipation and thermal derating behavior of the 1N5255B?

The 1N5255B is rated for 500 mW power dissipation at 25°C ambient or lead temperature. Derating begins linearly above 25°C at 4.0 mW/°C (based on 250 °C/W junction-to-lead thermal resistance), reaching zero power at 150°C. When mounted on FR4 PCB with specified copper pads, derating follows 3.2 mW/°C (310 °C/W junction-to-ambient), reaching zero at 103°C. These curves are documented in Figure 1 of the Microsemi datasheet.

Does the 1N5255B support military or space-grade screening?

Yes - the 1N5255B can be supplied with military screening prefixes (MQ, MX, MV, MSP) when ordered with the "-1" suffix (e.g., MQ1N5255B-1), enabling compliance with MIL-PRF-19500 for JAN, JANTX, JANTXV, and JANS levels. Radiation hardness is inherent per MicroNote 050, and ESD immunity is verified per MIL-STD-750 Method 1020. Standard 1N5255B units are commercial-grade unless explicitly ordered with screening prefixes.

What is the Zener impedance and why does it matter for the 1N5255B?

The 1N5255B specifies a maximum Zener impedance (Z_ZT) of 600 Ω at I_ZK = 0.25 mA, which reflects dynamic resistance near the knee of the breakdown curve. This value determines how tightly the voltage remains regulated under varying load current - lower Z_ZT yields smaller voltage deviations. At full test current (44 mA), impedance drops further, but the 600 Ω figure governs performance in low-current bias networks and precision references.

How is polarity marked and what is the correct orientation for regulation in the 1N5255B?

The 1N5255B uses a single black band to mark the cathode terminal. For Zener regulation, the banded (cathode) end must be held at a more positive potential than the unmarked (anode) end. Applying reverse bias in this orientation causes controlled avalanche breakdown at ~28 V. Forward bias yields typical silicon diode behavior (<1.5 V drop at 200 mA), but forward conduction is not its intended function.