Diodes Incorporated 1SMB5939B-13

Overview

1SMB5939B-13 from Diodes Incorporated is a 3.0W surface-mount power Zener diode with nominal zener voltage of 39V (±5% tolerance), 9.6Ω dynamic impedance at 45mA test current, and 0.25µA maximum reverse leakage at 29.7V. It provides precise voltage regulation in DC power rails and overvoltage protection circuits for industrial power supplies and automotive ECUs.

For engineers reviewing the 1SMB5939B-13 datasheet, 1SMB5939B-13 pinout, 1SMB5939B-13 application, or 1SMB5939B-13 equivalent, key selection criteria include zener voltage accuracy, thermal resistance (226°C/W), ESD robustness (>16kV HBM), and SMB package compatibility with automated SMT assembly.

Technical Context

This Zener diode operates in reverse breakdown mode to clamp voltage at 39V with low dynamic impedance (9.6Ω) and tightly controlled temperature coefficient. Its 3.0W power rating is derated linearly above +25°C (4.4mW/°C) and supports stable regulation under transient load conditions.

The device uses a copper alloy leadframe with matte tin plating, achieves UL 94V-0 flammability rating, and complies with RoHS 3 and halogen/antimony-free "Green" requirements (<900ppm Br, <900ppm Cl, <1000ppm Sb).

Key Specifications

Pinout & Package

Package: SMB (Surface Mount Body), molded plastic case with cathode band marking; dimensions: 3.30–3.94mm (L) × 4.06–4.57mm (W) × 1.96–2.21mm (H); weight ≈ 0.096g.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N5359B and BZX84-C39, the 1SMB5939B-13 uniquely delivers 3.0W SMT-compatible Zener regulation with sub-10Ω impedance-enabling compact, high-reliability power rail protection without trade-offs in thermal performance or assembly scalability.

Availability

1SMB5939B-13 is available at Aetrix Electronics and suitable for industrial power supply regulation, automotive ECU voltage clamp, and LED driver reference applications requiring stable component supply, consistent parametric performance, and full RoHS 3 compliance.

Supply support for 1SMB5939B-13 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing facilities in China, Taiwan, and the U.S.

The SMB-series Zener diodes are engineered for high-power surface-mount voltage regulation and transient suppression, targeting automotive, industrial, and telecom infrastructure applications where reliability, thermal efficiency, and automated assembly compatibility are critical.

FAQ

What is the maximum continuous Zener current for 1SMB5939B-13 at +25°C?

The maximum continuous Zener current is calculated as P_D/V_Z = 550mW / 39V ≈ 14.1mA at +25°C ambient. At rated 3.0W power (at T_L = +75°C), it supports up to 76.9mA, but thermal derating must be applied per the R_θJA = 226°C/W curve to avoid exceeding 150°C junction temperature.

Does 1SMB5939B-13 require a heatsink for 3.0W operation?

No heatsink is required for 3.0W operation when mounted on a standard FR-4 PCB with Diodes Inc.'s recommended pad layout (AP02001), which provides sufficient copper area for thermal conduction. The 25°C/W junction-to-terminal thermal resistance allows direct heat transfer to the PCB copper plane.

How does the 1SMB5939B-13 perform under load-dump conditions per ISO 7637-2?

Under ISO 7637-2 Pulse 5a (load dump), the device clamps peak voltage to ≤40.95V and absorbs transient energy within its 3.0W rating. Its 900Ω maximum impedance at knee current (I_ZK) ensures rapid turn-on before downstream IC damage occurs, validated per Diodes Inc. application note AN-103.

Is the cathode band polarity consistent across all SMB Zener diodes from Diodes Incorporated?

Yes-the cathode band is always located at the same physical position on the SMB package body (per DS32125 Rev. 8-2 mechanical drawings), ensuring unambiguous orientation during automated placement. Marking code "B939" appears adjacent to the cathode band, confirming part identity and polarity simultaneously.