onsemi 1N749A_T50R

Overview

1N749A_T50R from Fairchild Semiconductor is a 4.3 V, ±5% tolerance, 500 mW glass-passivated Zener diode in DO-35 package, rated for 85 mA maximum Zener current at 25°C and 30 µA reverse leakage at 1 V, used for precision voltage regulation and reference in low-power analog circuits.

For engineers reviewing the 1N749A_T50R datasheet, pinout, applications, or equivalent options, key selection considerations include zener voltage tolerance, thermal derating above 75°C, cathode band identification, and compatibility with through-hole PCB layouts requiring stable 4.3 V reference.

Technical Context

This Zener diode operates in reverse breakdown to maintain a stable 4.3 V reference across varying load currents, with dynamic impedance of 22 Ω at 20 mA test current. Its DO-35 glass package ensures hermetic sealing and reliable performance from –65°C to +200°C.

The device exhibits 2 µA reverse leakage at VR = 1 V (25°C), rising to 30 µA at 125°C, and follows standard JEDEC power derating: 4.0 mW/°C above 75°C ambient, limiting usable dissipation to 340 mW at 160°C lead temperature.

Key Specifications

Pinout & Package

DO-35 glass axial package with cathode identified by a single color band on the body. Leads are tinned copper, suitable for wave or hand soldering per J-STD-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N749A_T50R, the base 1N749A offers identical electrical performance in bulk form for hand assembly, while BZX55-C4V3 provides marginally better dynamic regulation at the cost of non-Fairchild sourcing and minor marking differences.

Availability

1N749A_T50R is available at Aetrix Electronics and suitable for industrial sensor signal conditioning, low-power microcontroller reference, and automotive cabin control panel applications requiring stable component supply and long-lifecycle support.

Supply support for 1N749A_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 1N746A–1N759A series was designed as a general-purpose, cost-optimized family of through-hole Zener diodes for voltage regulation and reference in industrial, consumer, and legacy automotive electronics.

FAQ

What is the exact Zener voltage tolerance for 1N749A_T50R?

The 1N749A_T50R has a guaranteed ±5% tolerance on its nominal 4.3 V Zener voltage, meaning the actual measured V_Z at I_Z = 20 mA falls between 4.09 V and 4.52 V across the full operating temperature range. This tolerance is specified per JEDEC standard and verified during final test screening. The 1N749A_T50R maintains this specification without binning or sorting.

Does 1N749A_T50R require heatsinking in typical applications?

No, the 1N749A_T50R does not require external heatsinking when operated within its 500 mW power limit at lead temperature ≤75°C. Its DO-35 package relies on lead conduction for thermal dissipation; standard 3/8″ lead length provides sufficient thermal path. At ambient temperatures above 75°C, derating to 4.0 mW/°C applies - for example, only 340 mW is allowed at 160°C lead temperature. The 1N749A_T50R is typically used in low-current reference roles where power dissipation remains well below 100 mW.

How is cathode polarity marked on the 1N749A_T50R DO-35 package?

The cathode of the 1N749A_T50R is marked by a single color band (typically black or dark gray) located near one end of the DO-35 glass body. This band identifies the cathode terminal, which must be connected to the higher-potential node in Zener regulation configurations. The anode is the unmarked lead. This marking convention is consistent across the entire 1N746A–1N759A series and complies with JEDEC standards. The 1N749A_T50R uses the same physical marking as all Fairchild DO-35 Zeners.

Can 1N749A_T50R replace 1N749A in existing designs?

Yes, the 1N749A_T50R is a direct form-fit-function replacement for the bulk-packaged 1N749A, sharing identical electrical specifications, DO-35 package dimensions, pinout, and thermal characteristics. The "_T50R" suffix indicates tape-and-reel packaging per EIA-481-D for automated placement; no circuit or layout changes are needed. All parameters - including 4.3 V V_Z, 22 Ω Z_Z, and 85 mA I_ZM - match the original 1N749A. The 1N749A_T50R is fully compatible with legacy designs using 1N749A.

What is the maximum reverse leakage current for 1N749A_T50R at elevated temperature?

At 125°C junction temperature, the 1N749A_T50R exhibits a maximum reverse leakage current of 30 µA when measured at V_R = 1 V, per the manufacturer's datasheet. This is higher than the 2 µA specified at 25°C but remains within acceptable limits for most reference applications. The 1N749A_T50R's leakage behavior is fully characterized and documented across the –65°C to +200°C operating range, supporting reliable use in high-temperature industrial environments.