40V Bidirectional TVS in DO-214AB – Surge Protection for 24V Rails and Signal Lines
The SMCJ40CAE3/TR13 is a bidirectional Zener TVS diode from Microchip Technology, rated for 1500 W peak pulse power (10/1000 µs waveform) with a reverse standoff voltage of 40 V. The 64.5 V clamping voltage at 23.2 A peak pulse current defines the upper voltage the protected circuit sees during a surge — important when the downstream silicon has a 60 V absolute maximum rating. The single bidirectional channel clamps both polarities, so one device replaces two unidirectional TVS diodes in anti-series on AC or bipolar signal lines.
Clamping Voltage and Peak Current – Matching the TVS to the Protected Rail
The 40 V reverse standoff is the maximum continuous DC voltage the TVS will not conduct at; for a nominal 24 V DC rail this provides healthy margin, but a 48 V rail exceeds it and the device would leak. The minimum breakdown voltage is 44.4 V, so the TVS starts clamping just above the standoff. The clamping voltage of 64.5 V at 23.2 A peak pulse current is the worst-case voltage the load sees — verify this stays below the absolute maximum rating of the protected ICs. For a 24 V system the margin is generous; for a 36 V rail the 64.5 V clamp may stress 40 V-rated parts.
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