onsemi 1N5255B

Overview

1N5255B from Fairchild Semiconductor is a 28 V ±5% Zener diode in DO-35 glass package, rated for 500 mW power dissipation at 25°C, with 44 Ω dynamic impedance at 20 mA test current and 0.1 μA reverse leakage at 22.4 V. It serves as a precision voltage reference or overvoltage clamp in low-power analog circuits and power supply feedback paths.

For engineers reviewing the 1N5255B datasheet, pinout, applications, or equivalent options, key selection criteria include its 28 V nominal Zener voltage, ±5% tolerance, DO-35 axial package compatibility, thermal coefficient of +0.090 %/°C, and suitability for voltage regulation in space-constrained linear regulators and sensor bias networks.

Technical Context

The 1N5255B operates as a two-terminal silicon Zener diode optimized for stable breakdown in the 28 V range. Its design targets low-noise, temperature-stable voltage reference applications where tight voltage tolerance and predictable TC are required. The device uses planar-diffused junction construction in a hermetically sealed DO-35 glass package.

It exhibits a typical forward voltage of ≤1.2 V at 200 mA and maintains 0.1 μA maximum reverse leakage at VR = 22.4 V (80% of VZ). Its 44 Ω Zener impedance at IZ = 20 mA supports stable regulation under moderate load transients without external buffering.

Key Specifications

Pinout & Package

DO-35 glass package: axial-leaded, hermetically sealed, cathode indicated by color band. Overall length 4.56 mm, body diameter 1.91 mm, lead diameter 0.46 mm. Weight: 0.137 g.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N4749A and BZX55-C27, the 1N5255B offers tighter thermal coefficient control (+0.090 %/°C vs. unspecified or ±0.1 %/°C), DO-35 size compatibility for space-constrained layouts, and optimized 20 mA test-point impedance-making it preferable for precision low-power reference roles where thermal stability and footprint are prioritized over raw power headroom.

Availability

1N5255B is available at Aetrix Electronics and suitable for low-power voltage reference, overvoltage protection, and feedback stabilization applications requiring stable component supply and consistent parametric performance across production batches.

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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The 1N52xxB series was designed as a general-purpose, high-reliability Zener diode family for voltage regulation and reference in commercial-grade industrial and consumer electronics.

FAQ

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

The 1N5255B has a nominal Zener voltage of 28 V with a tolerance of ±5%, meaning its actual breakdown voltage falls between 26.6 V and 29.4 V when tested at 20 mA. This specification is guaranteed per the Fairchild 1N5221B–1N5263B datasheet Rev. 4.10 and applies to all units meeting the 1N5255B marking standard. The 1N5255B achieves this accuracy through controlled diffusion and wafer-level sorting.

What is the maximum power dissipation rating for the 1N5255B and how does it change with temperature?

1N5255B is rated for 500 mW power dissipation at ambient temperature (TA) of 25°C. Above 50°C, it must be derated at 4.0 mW/°C - for example, at 75°C ambient, maximum allowable power drops to 400 mW. This linear derating ensures safe junction temperature operation up to TJ = +200°C. The 1N5255B's DO-35 glass package enables reliable thermal performance within these limits.

Does the 1N5255B have a specified forward voltage, and what is its value?

Yes, the 1N5255B specifies a maximum forward voltage (VF) of 1.2 V at forward current (IF) of 200 mA. This parameter is defined in the "Electrical Characteristics" section of the Fairchild datasheet and reflects the diode's anode-to-cathode conduction drop under high-current forward bias. While primarily used in reverse breakdown, this VF rating ensures predictable behavior if the 1N5255B is inadvertently forward-biased in circuit fault conditions.

What is the Zener impedance (ZZ) of the 1N5255B and why does it matter in regulation circuits?

The 1N5255B has a Zener impedance (ZZ) of 44 Ω measured at IZ = 20 mA. This value quantifies how much the output voltage changes per unit change in current - lower ZZ means better regulation under varying load. In practice, a 44 Ω impedance means a 1 mA load shift causes ~44 mV output variation. This makes the 1N5255B suitable for applications demanding moderate regulation stability without active buffering, such as sensor biasing or feedback node stabilization.

How is the cathode identified on the 1N5255B DO-35 package?

The cathode of the 1N5255B is marked by a distinct color band (typically black or dark stripe) located near one end of the DO-35 glass body. Per JEDEC DO-204AH standard and Fairchild's marking specification, this band identifies the cathode terminal, which must be connected to the higher-potential side of the circuit during Zener operation. The 1N5255B's top mark includes "F" logo, "25", and "5B" - confirming its identity and distinguishing it from adjacent variants like 1N5254B or 1N5256B.