onsemi BZX85C39_T50R

Overview

BZX85C39_T50R from onsemi is a 39 V ±5% tolerance, 1.0 W axial-leaded Zener diode in DO-41 glass package, with 6 Ω zener impedance at 45 mA test current and 0.25 μA max leakage at 29.7 V reverse voltage, used for precision voltage regulation in power supply feedback loops and overvoltage protection circuits.

For engineers reviewing the BZX85C39_T50R datasheet, pinout, applications, or equivalent options, key selection criteria include zener voltage tolerance, power derating above 50°C (6.67 mW/°C), thermal resistance (150°C/W junction-to-ambient), and cathode band polarity marking per JEDEC DO-41 standard.

Technical Context

This device operates as a two-terminal voltage reference with stable breakdown behavior under reverse bias, specified at 45 mA test current and 30°C lead temperature per ON Semiconductor's measurement methodology. Its 200°C maximum junction temperature and -65°C to +200°C storage range support high-reliability industrial and automotive environments.

The DO-41 glass package provides hermetic sealing and low thermal resistance, enabling reliable operation at full 1.0 W dissipation only at TA = 25°C; power must be linearly derated above 50°C. Forward voltage is 1.2 V max at 200 mA, confirming silicon PN junction construction.

Key Specifications

Pinout & Package

DO-41 glass axial package with cathode indicated by a single color band on the body; leads are unmarked but electrically symmetric except for polarity - cathode is the banded end, anode is the unbanded end.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX85C39_T50R, the 1N4739A trades hermetic reliability for lower cost and wider distributor availability, while the BZX85C39-TR offers identical performance in a different packaging format for automated manufacturing - neither is pin-compatible drop-in replacement due to distinct ordering suffixes governing packaging and traceability.

Availability

BZX85C39_T50R is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, and sensor interface circuits requiring stable component supply with guaranteed long-term availability and traceable lot-level documentation.

Supply support for BZX85C39_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

onsemi (formerly ON Semiconductor) is a global semiconductor manufacturer specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The BZX85C series was designed specifically for high-reliability voltage regulation and clamping in harsh-environment applications, emphasizing hermetic packaging, wide temperature operation, and tight parametric consistency across production lots.

FAQ

What is the zener voltage tolerance of BZX85C39_T50R?

The BZX85C39_T50R has a nominal zener voltage of 39 V with a tolerance of ±5%, meaning its actual breakdown voltage falls between 37.05 V and 40.95 V when measured at 45 mA and 30°C lead temperature. This tolerance is confirmed in the Electrical Characteristics table of the official ON Semiconductor datasheet (Rev. 2, October 2017) and applies strictly to the BZX85C39_T50R variant.

Can BZX85C39_T50R replace BZX85C36 or BZX85C43 in the same circuit?

No - BZX85C39_T50R is not a direct substitute for BZX85C36 (36 V) or BZX85C43 (43 V), as each part has a distinct nominal zener voltage and corresponding test conditions. Swapping would shift regulation or clamping thresholds by ±3–4 V, potentially causing overvoltage damage or undervoltage shutdown. The BZX85C39_T50R must be used only where 39 V ±5% regulation is explicitly required.

What is the maximum allowable power dissipation for BZX85C39_T50R at 75°C ambient?

At 75°C ambient, BZX85C39_T50R must be derated from its 1.0 W rating at 25°C. With a derating factor of 6.67 mW/°C above 50°C, the allowable power is 1.0 W − (75 − 50) × 0.00667 W = 0.833 W. This value assumes free-air convection and no heatsinking; PCB copper area or forced airflow may improve thermal performance.

Is BZX85C39_T50R suitable for automotive applications?

Yes - BZX85C39_T50R meets key automotive requirements: it operates from -65°C to +200°C, uses a hermetic DO-41 glass package resistant to humidity and thermal cycling, and is manufactured by onsemi, whose Zener diodes are widely deployed in AEC-Q101-compliant systems. However, final qualification depends on board-level testing per ISO 16750 and customer-specific stress screening.

How is the cathode identified on BZX85C39_T50R?

The cathode of BZX85C39_T50R is marked by a single color band on the glass body of the DO-41 package. This band must be oriented toward the more positive node in the circuit - i.e., the cathode connects to the voltage being regulated or clamped, while the anode connects to ground or the lower-potential rail. This marking follows JEDEC DO-204AL standard and is verified in the Physical Dimensions section of the datasheet.