Taiwan Semiconductor Corporation SMDJ78A

Overview

SMDJ78A from Taiwan Semiconductor is a unidirectional 3000W surface-mount transient voltage suppressor (TVS) diode with a 78V working stand-off voltage, 86.7–95.8V breakdown voltage at 1mA, and 126V maximum clamping voltage at 23.8A peak pulse current. It is designed for robust ESD and surge protection in DC power rails of industrial control systems, automotive electronics, and telecom infrastructure.

For engineers reviewing the SMDJ78A datasheet, SMDJ78A pinout, SMDJ78A application, or SMDJ78A equivalent, key selection criteria include its DO-214AB (SMC) package compatibility, ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance, sub-1ps response time, 175°C junction rating, and verified clamping performance under 10/1000μs transients.

Technical Context

The SMDJ78A operates as a unidirectional avalanche diode, conducting only in reverse bias above its breakdown threshold to clamp transient energy into ground. Its glass-passivated junction ensures stable V_BR tolerance and long-term reliability under repeated surge stress.

It delivers 3000W peak pulse power (10/1000μs waveform), supports 300A non-repetitive forward surge current (8.3ms half-sine), and maintains thermal stability via low R_θJL = 15°C/W and R_θJA = 75°C/W - enabling high-power transient suppression without external heatsinking in standard PCB layouts.

Key Specifications

Pinout & Package

Package: DO-214AB (SMC), surface-mount, single-diode configuration with cathode band marking. Matte tin-plated leads, JEDEC-compliant solderability, UL 94V-0 molding compound, and JESD201 Class 2 whisker resistance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar transient voltage suppression applications.

Compared with SMAJ78A and SMCJ78A, the SMDJ78A provides identical 3000W surge capability and DO-214AB packaging as SMCJ78A - ensuring direct mechanical and thermal compatibility - while offering tighter V_BR tolerance than many legacy SMCJ variants, improving clamping consistency in high-volume production.

Availability

SMDJ78A is available at Aetrix Electronics and suitable for industrial motor drives, automotive body control modules, and telecom power feeds requiring stable component supply, long-lifecycle support, and traceable sourcing for mission-critical surge protection.

Supply support for SMDJ78A 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

Taiwan Semiconductor Corporation (TSC) is a vertically integrated analog and discrete semiconductor manufacturer headquartered in Hsinchu, Taiwan, specializing in high-reliability protection devices, rectifiers, and power management components.

The SMDJ series belongs to TSC's high-power surface-mount TVS portfolio, engineered specifically for automotive, industrial, and telecom applications demanding ISO 7637-2 compliance, extended temperature operation, and robust surge immunity without derating.

FAQ

What is the maximum clamping voltage of the SMDJ78A under a 3000W transient?

The SMDJ78A has a maximum clamping voltage (V_C) of 126 V at 23.8 A peak pulse current, corresponding to the standardized 10/1000 μs double-exponential surge waveform. This value is guaranteed across the full operating temperature range and defines the upper voltage limit imposed on protected circuits during worst-case transients. The SMDJ78A maintains this clamping performance consistently due to its glass-passivated junction and thermally optimized DO-214AB package.

Is the SMDJ78A suitable for bidirectional surge protection?

No, the SMDJ78A is a unidirectional TVS diode intended for DC rail protection where polarity is fixed. For bidirectional applications such as AC lines or data buses like RS-485, the SMDJ78CA variant must be used - it features symmetrical breakdown in both directions and identical clamping specs. The SMDJ78A's cathode band marking and single-diode construction confirm its unidirectional functionality; using it in reverse-biased AC contexts will not provide protection.

What is the junction-to-lead thermal resistance (R_θJL) of the SMDJ78A?

The SMDJ78A has a typical junction-to-lead thermal resistance (R_θJL) of 15°C/W, measured from die to solder joint under standard test conditions. This low value enables efficient heat transfer from the silicon junction to the PCB copper, supporting reliable 3000W pulse handling without external heatsinking. When designing layouts for the SMDJ78A, ensure adequate copper pour connected to both terminals to fully leverage this thermal performance and maintain T_J ≤ 175°C during repetitive surge events.

Does the SMDJ78A meet RoHS and halogen-free requirements?

Yes, the SMDJ78A is RoHS compliant and halogen-free per IEC 61249-2-21. Its molding compound contains no brominated flame retardants or chlorine-based additives, and all plating materials meet EU Directive 2011/65/EU restrictions. The device also achieves moisture sensitivity level 1 (per J-STD-020), eliminating the need for dry-pack or baking prior to SMT reflow - simplifying manufacturing for high-reliability electronics producers.

How does the SMDJ78A compare to the SMDJ75A in terms of clamping performance?

The SMDJ78A clamps at 126 V (23.8 A), while the SMDJ75A clamps at 121 V (24.8 A). Though the SMDJ75A has slightly lower V_C, the SMDJ78A offers higher V_WM (78 V vs. 75 V), making it better suited for 72–80 V nominal systems where margin against false triggering is critical. Both share identical 3000W rating and DO-214AB packaging, so layout reuse is possible - selection depends on system voltage tolerance and required standoff headroom.