Taiwan Semiconductor Corporation SMCJ78

Overview

SMCJ78 from Taiwan Semiconductor is a unidirectional 1500W surface-mount transient voltage suppressor (TVS) diode in DO-214AB (SMC) package, with 78V working stand-off voltage (VWM), 86.7–106V breakdown voltage (VBR), and 139V maximum clamping voltage (VC) at 11.3A peak impulse current - designed for automotive load-dump and inductive switching surge protection in power supply rails.

For engineers reviewing the SMCJ78 datasheet, SMCJ78 pinout, SMCJ78 application, or SMCJ78 equivalent, key selection criteria include clamping voltage margin vs. protected IC VDD rating, peak pulse power handling under ISO 7637-2 Pulse 5a, thermal derating above 25°C ambient, and unidirectional polarity alignment with DC rail topology.

Technical Context

The SMCJ78 employs a glass-passivated silicon junction optimized for sub-nanosecond response (<1.0 ps from 0 V to VBR min) and low leakage (<1 µA at 78 V), meeting ISO 7637-2 Pulse 1/2a/2b/3a/3b immunity requirements. Its single-die unidirectional structure provides asymmetric conduction - forward-biased during overvoltage events on positive rails only.

Thermal performance is defined by R_θJA = 55°C/W and R_θJC = 10°C/W, enabling sustained operation up to T_J = 150°C. The device sustains 200 A non-repetitive forward surge (8.3 ms half-sine) and exhibits VF = 3.5 V @ 100 A - consistent with SMCJ5.0–SMCJ90 series specifications.

Key Specifications

Pinout & Package

Package: DO-214AB (SMC), surface-mount, matte tin-plated leads, polarity indicated by cathode band. Weight: 0.210 g. UL 94V-0 molding compound.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ78A and 1.5KE78A, the SMCJ78 uniquely combines 1500 W surface-mount capability, sub-1 ps response, and full ISO 7637-2 certification - making it the only option among the three qualified for automotive power rail protection without layout or qualification compromise.

Availability

SMCJ78 is available at Aetrix Electronics and suitable for automotive electronic control units, industrial motor drives, outdoor LED lighting systems, and telecom DC feeder protection requiring stable component supply across extended production lifecycles.

Supply support for SMCJ78 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 TVS diodes, rectifiers, MOSFETs, and power management devices since 1979.

The SMCJ series belongs to TSC's high-power transient suppression product line, engineered specifically for automotive and industrial applications demanding ISO 7637-2 compliance, high surge robustness, and surface-mount manufacturability.

FAQ

What is the clamping voltage of SMCJ78 and how is it measured?

The SMCJ78 has a maximum clamping voltage (VC) of 139 V, measured at 11.3 A peak impulse current (IPPM) using the 10/1000 µs double-exponential waveform defined in Fig.5 of the datasheet. This value represents the highest voltage the device allows across its terminals during a standardized surge event, directly determining the overvoltage stress imposed on protected downstream components. The test condition is strictly defined and repeatable per ANSI/IEEE C62.35.

Is SMCJ78 suitable for bidirectional transient protection?

No, the SMCJ78 is a unidirectional TVS diode and is not rated for bidirectional operation. It clamps only positive transients on the cathode-connected rail relative to anode (ground). For bidirectional protection, the SMCJ78CA variant - which carries a "CA" suffix and features symmetrical breakdown in both directions - must be used instead. Using SMCJ78 in a bidirectional configuration risks failure during negative-going surges.

Does SMCJ78 meet automotive qualification standards such as AEC-Q200?

The SMCJ78 is designed to meet ISO 7637-2 Pulse 1/2a/2b/3a/3b immunity requirements and is widely deployed in automotive applications, but Taiwan Semiconductor does not list AEC-Q200 qualification for this specific part in its official documentation. Engineers requiring formal AEC-Q200 compliance should verify qualification status directly with TSC or select explicitly certified alternatives such as the SMAJ78A-Q or similar AEC-Q200 listed variants.

What is the forward voltage drop of SMCJ78 under high-current surge conditions?

The SMCJ78 exhibits a forward voltage (VF) of 3.5 V at 100 A, per Note 2 in the Absolute Maximum Ratings table. This value applies during unidirectional 8.3 ms half-sine surge events and reflects the voltage drop across the device when conducting large forward currents - critical for estimating power dissipation and thermal rise during repetitive surge testing or fault conditions.

How does the SMCJ78 compare to SMCJ78A in terms of electrical performance?

The SMCJ78A offers tighter breakdown voltage tolerance (86.7–95.8 V vs. 86.7–106 V for SMCJ78) and lower clamping voltage (126 V vs. 139 V), resulting in improved overvoltage protection margin. Both share identical package (DO-214AB), power rating (1500 W), and ISO 7637-2 compliance. The SMCJ78A is preferred where precise clamping control is needed, while SMCJ78 remains valid for applications with wider voltage margin allowances.