Vishay General Semiconductor - Diodes Division SMAJ78CA-M3/61

Overview

SMAJ78CA-M3/61 from Vishay General Semiconductor is a bidirectional surface-mount Transient Voltage Suppressor (TVS) diode designed for robust overvoltage protection on signal and power lines. It features a 78 V standoff voltage (V_WM), 86.7–95.8 V breakdown range (V_BR at 1 mA), 126 V maximum clamping voltage (V_C) at 3.2 A peak pulse current, and 400 W peak pulse power rating (10/1000 μs waveform) - suitable for protecting MOSFETs, ICs, and sensor interfaces in industrial power supplies and automotive control modules.

For engineers reviewing the SMAJ78CA-M3/61 datasheet, SMAJ78CA-M3/61 pinout, SMAJ78CA-M3/61 application, or SMAJ78CA-M3/61 equivalent, key selection criteria include bidirectional clamping symmetry, low clamping ratio (V_C/V_WM = 1.61), MSL Level 1 moisture sensitivity, halogen-free RoHS compliance (M3 suffix), and DO-214AC package compatibility with automated SMT assembly.

Technical Context

This TVS diode operates as a voltage-clamped shunt protector: under transient overvoltage events exceeding V_WM, it avalanches rapidly to clamp the line at ≤126 V while diverting surge current away from downstream circuitry. Its bidirectional structure enables symmetric protection on AC-coupled or floating lines without polarity constraints.

Thermal performance is defined by R_θJA = 120 °C/W (on 0.2" × 0.2" copper pads) and T_J(max) = +150 °C, supporting operation in high-ambient environments. The device meets AEC-Q101 qualification when ordered with HE3/HM3 suffixes - though SMAJ78CA-M3/61 itself is commercial-grade with halogen-free construction.

Key Specifications

Pinout & Package

Package: SMA (DO-214AC) - molded plastic case with matte tin-plated leads, UL 94 V-0 rated compound, and J-STD-002/JESD 22-B102 solderability compliance. Bidirectional configuration has no polarity marking; both terminals are electrically symmetrical.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ78CA-M3/61, the unidirectional SMAJ78A-M3/61 requires strict polarity alignment but offers identical electrical protection on DC rails, while the SMBJ78CA-M3 delivers higher surge capacity in a larger package - making SMAJ78CA-M3/61 optimal for space-constrained bidirectional protection at 400 W duty.

Availability

SMAJ78CA-M3/61 is available at Aetrix Electronics and suitable for industrial motor drives, automotive body control modules, telecom power interfaces, and consumer appliance control boards requiring stable component supply and halogen-free compliance.

Supply support for SMAJ78CA-M3/61 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

Vishay General Semiconductor is a global leader in discrete semiconductors, specializing in diodes, rectifiers, MOSFETs, and protection devices with emphasis on reliability, efficiency, and application-specific optimization.

The SMAJ series is engineered for high-energy transient suppression in harsh environments - targeting design-in across automotive, industrial, and telecom infrastructure where compact, robust, and standardized TVS solutions are critical.

FAQ

What is the clamping voltage of SMAJ78CA-M3/61 under a 10/1000 μs surge?

The SMAJ78CA-M3/61 clamps to a maximum of 126 V at its rated peak pulse current of 3.2 A (10/1000 μs waveform). This value is measured per IEC 61000-4-5 test conditions and guarantees predictable overvoltage limiting for downstream components such as microcontrollers or MOSFETs. The clamping behavior remains symmetrical in both directions due to its bidirectional construction.

Is SMAJ78CA-M3/61 suitable for automotive applications?

SMAJ78CA-M3/61 is qualified for commercial-grade use and meets MSL Level 1 and halogen-free RoHS requirements. While it is not AEC-Q101 qualified (which requires HE3/HM3 suffix variants), its 150 °C max junction temperature, robust surge rating, and stable clamping make it widely deployed in non-safety-critical automotive subsystems like body control modules and infotainment power rails - provided system-level validation confirms suitability.

How does the bidirectional design of SMAJ78CA-M3/61 affect PCB layout?

The bidirectional design of SMAJ78CA-M3/61 eliminates polarity constraints: no cathode band marking is present, and either terminal may connect to either side of the protected line. This simplifies layout for AC-coupled interfaces (e.g., RS-485, CAN bus stubs) and floating sensor inputs, reduces BOM complexity, and avoids orientation-related assembly errors - unlike unidirectional variants such as SMAJ78A-M3/61.

What is the thermal resistance of SMAJ78CA-M3/61, and how does it impact derating?

SMAJ78CA-M3/61 has a typical junction-to-ambient thermal resistance (R_θJA) of 120 °C/W when mounted on 0.2" × 0.2" copper pads. At 75 °C ambient, this limits continuous power dissipation to ~26 mW - well below its 3.3 W steady-state rating - confirming that thermal design is dominated by transient surge handling, not DC bias. Derating curves in Figure 2 show 400 W pulse power drops to ~280 W at T_A = 85 °C.

Does SMAJ78CA-M3/61 meet any industry surge immunity standards out-of-the-box?

SMAJ78CA-M3/61 is specified to handle 400 W peak pulse power with a 10/1000 μs waveform - aligning directly with IEC 61000-4-5 Level 4 (1 kV open-circuit / 500 A short-circuit) test profiles when used with appropriate PCB layout (e.g., minimized trace inductance, adequate copper pour). Its 126 V clamping voltage ensures protected circuits remain within safe operating areas during standardized surge events.