onsemi BZX55C18_T50A

Overview

BZX55C18_T50A from Fairchild Semiconductor is a 18 V ±5% Zener diode in DO-35 glass package, rated for 500 mW power dissipation at TL ≤ 75°C with 4.0 mW/°C derating above that temperature, and specified for operation from –65°C to +200°C. It delivers stable voltage regulation in low-power reference and protection circuits, such as overvoltage clamping in sensor signal conditioning or biasing networks in analog front-ends.

For engineers reviewing the BZX55C18_T50A datasheet, pinout, applications, or equivalent options, key selection criteria include its 18 V nominal Zener voltage at 5 mA test current, 50 Ω dynamic impedance at IZ, 0.1 μA reverse leakage at 14.4 V, 14 mA maximum Zener current, and DO-35 mechanical compatibility with legacy through-hole designs.

Technical Context

The BZX55C18_T50A operates as a silicon planar Zener diode relying on controlled avalanche breakdown for precise voltage regulation. Its 18 V nominal Zener voltage is guaranteed between 17.1 V (min) and 19.1 V (max) at 5 mA test current, with dynamic impedance of 50 Ω measured under same conditions.

It exhibits 0.1 μA reverse leakage current at VR = 14.4 V (80% of VZ), supports forward conduction up to 1.3 V at 100 mA, and maintains thermal stability across –65°C to +200°C operating and storage range - critical for automotive under-hood and industrial control environments.

Key Specifications

Pinout & Package

DO-35 glass axial package with cathode indicated by color band; two-terminal device with no internal connections beyond anode and cathode.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N4746A and BZX55C18-TP, the BZX55C18_T50A offers optimal fit for space-constrained, thermally limited designs requiring exact DO-35 compatibility and 500 mW steady-state operation - not oversized power or alternate sourcing alone.

Availability

BZX55C18_T50A is available at Aetrix Electronics and suitable for automotive sensor biasing, industrial analog reference generation, and legacy equipment voltage clamping requiring stable component supply and long-term obsolescence management.

Supply support for BZX55C18_T50A 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 BZX55 series was developed as a general-purpose, cost-optimized Zener diode family targeting voltage regulation and protection in consumer, industrial, and automotive electronics with standardized DO-35 packaging.

FAQ

What is the Zener voltage tolerance for BZX55C18_T50A?

The BZX55C18_T50A has a ±5% Zener voltage tolerance, meaning its nominal 18 V rating spans 17.1 V (minimum) to 19.1 V (maximum) when measured at 5 mA test current and 25°C. This tolerance is factory-tested and guaranteed per the Fairchild BZX55C2V4–BZX55C56 datasheet Rev. D1. The BZX55C18_T50A achieves this consistency using planar diffusion process control and batch calibration.

What is the maximum power dissipation of BZX55C18_T50A and how does it change with temperature?

The BZX55C18_T50A is rated for 500 mW power dissipation at lead temperature (TL) ≤ 75°C with 3/8″ lead length. Above 75°C, it derates linearly at 4.0 mW/°C - for example, at TL = 100°C, maximum allowable power drops to 400 mW. This derating curve is defined in the Absolute Maximum Ratings table of the BZX55C18_T50A datasheet and reflects junction-to-lead thermal resistance limitations.

What is the reverse leakage current specification for BZX55C18_T50A?

The BZX55C18_T50A specifies a maximum reverse leakage current (IR) of 0.1 μA when reverse voltage (VR) is applied at 14.4 V - equivalent to 80% of its nominal Zener voltage. This value is measured at 25°C and guarantees minimal loading on high-impedance circuits such as op-amp bias networks or microcontroller input protection stages. The BZX55C18_T50A maintains this low IR across its full operating temperature range.

Does BZX55C18_T50A have a defined forward voltage characteristic?

Yes, the BZX55C18_T50A specifies a maximum forward voltage (VF) of 1.3 V at forward current (IF) = 100 mA, consistent with standard silicon diode behavior. This parameter is relevant when the device is used in forward conduction mode - for example, in polarity protection or ESD shunt paths. The BZX55C18_T50A's VF is verified during production testing and documented in the "Electrical Characteristics" section of its official datasheet.

What package type is used for BZX55C18_T50A and how is polarity marked?

The BZX55C18_T50A uses the DO-35 glass axial package with cathode identified by a single color band near one lead end. This marking convention follows JEDEC standards and matches the physical layout shown in the Fairchild BZX55C18_T50A top-marking diagram. The DO-35 case provides hermetic sealing and thermal performance suitable for reflow and wave soldering, and the BZX55C18_T50A's mechanical dimensions align precisely with industry-standard DO-35 footprints.