onsemi 1N957B_T50R

Overview

1N957B_T50R from Fairchild Semiconductor is a 6.8 V, ±5% tolerance, 500 mW glass-passivated Zener diode in DO-35 package, designed for precision voltage regulation and reference applications in power supply feedback loops, overvoltage protection circuits, and analog signal conditioning. It exhibits 18.5 Ω dynamic impedance at 5 mA and operates across –65°C to +200°C.

For engineers reviewing the 1N957B_T50R datasheet, pinout, applications, or equivalent options, key selection criteria include zener voltage tolerance (±5%), thermal stability up to +200°C, low leakage (<1.0 μA at 5.2 V), DO-35 mechanical compatibility, and derating behavior above 75°C.

Technical Context

The 1N957B_T50R functions as a two-terminal voltage reference device with sharp reverse-breakdown characteristics. Its zener voltage is specified at 5 mA test current (IZ = 5 mA), with typical dynamic impedance of 18.5 Ω and knee impedance (ZZK) of 47 Ω at IZK = 1.0 mA.

It is rated for 500 mW power dissipation at lead temperature ≤75°C, with linear derating of 4.0 mW/°C above that threshold. The device uses a glass-encapsulated DO-35 package with cathode band marking and supports operation across an extended industrial temperature range (–65°C to +200°C).

Key Specifications

Pinout & Package

DO-35 glass axial package with cathode identified by color band. Two-terminal device: Anode (unmarked end) and Cathode (banded end). No internal connections beyond the two leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N4734A and BZX55C6V8, the 1N957B_T50R offers identical voltage and tolerance in the compact DO-35 form factor, with proven high-temperature capability up to +200°C - making it optimal for space-constrained, thermally demanding applications where 500 mW suffices.

Availability

1N957B_T50R is available at Aetrix Electronics and suitable for switch-mode power supplies, overvoltage protection circuits, and industrial sensor signal conditioning requiring stable component supply, long-lifecycle support, and consistent parametric performance.

Supply support for 1N957B_T50R 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 1N957B_T50R belongs to Fairchild's legacy 1N9xxB Zener diode family, engineered for high-reliability voltage reference and regulation in industrial, automotive, and telecom infrastructure applications.

FAQ

What is the nominal zener voltage and tolerance of the 1N957B_T50R?

The 1N957B_T50R has a nominal zener voltage of 6.8 V with a tolerance of ±5%, measured at a test current of 5 mA. This specification is guaranteed across the full operating temperature range and reflects the device's role as a mid-precision voltage reference. The 1N957B_T50R achieves this accuracy using glass-passivated junction technology and tight process control during manufacturing.

What is the maximum power dissipation and derating behavior of the 1N957B_T50R?

The 1N957B_T50R is rated for 500 mW power dissipation at a lead temperature (T_L) of ≤75°C with 3/8″ lead length. Above 75°C, it derates linearly at 4.0 mW/°C. This behavior is defined in the Absolute Maximum Ratings table and must be applied in thermal design to avoid junction overheating. The 1N957B_T50R's DO-35 package relies on lead conduction for heat transfer, so layout and lead length directly impact real-world power handling.

What is the zener impedance of the 1N957B_T50R and why does it matter?

The 1N957B_T50R exhibits a typical zener impedance (Z_Z) of 18.5 Ω at 5 mA test current, indicating how tightly it maintains its regulated voltage under varying load conditions. Lower Z_Z means smaller output voltage deviation for a given current change - critical in feedback loops and reference circuits. The 1N957B_T50R's 18.5 Ω value ensures stable regulation even with moderate load transients, distinguishing it from higher-impedance general-purpose Zeners.

What package type and marking does the 1N957B_T50R use?

The 1N957B_T50R uses the DO-35 glass axial package with cathode identified by a color band. Marking consists of three lines: Fairchild logo (F) on line 1, "57" on line 2, and "B" on line 3 - conforming to Fairchild's top-marking standard for 1Nxx series devices. This marking scheme enables rapid visual identification and traceability of the 1N957B_T50R in automated assembly and field repair.

What is the operating temperature range of the 1N957B_T50R and how does it compare to standard Zeners?

The 1N957B_T50R operates from –65°C to +200°C, significantly exceeding the –65°C to +150°C range typical of many plastic-packaged Zeners. This extended range stems from its glass-encapsulated DO-35 construction and robust junction design, enabling reliable use in under-hood automotive, downhole instrumentation, and high-ambient industrial controls. The 1N957B_T50R's +200°C rating is confirmed in the Absolute Maximum Ratings table and validated across production lots.