TVS diode for 24 V / 28 V rail protection
The STMicroelectronics SM15T39A is a unidirectional Zener-type transient-voltage-suppression diode from the TRANSIL™ SM15T series. It is designed to clamp overvoltage transients on DC power rails, signal lines, and general-purpose circuits where a single-direction clamp is sufficient. The part is rated for a peak pulse power of 1500 W (1.5 kW) under the 10/1000 µs waveform, with a reverse standoff voltage of 33.3 V — meaning it will not conduct appreciably below that level, so it sits quietly on a 24 V or 28 V rail without leakage issues. Breakdown occurs at a minimum of 37.1 V, and the clamping voltage is held to 69.7 V at the peak pulse current of 143 A (8/20 µs waveform). This combination makes it a fit for protecting downstream converters, sensors, or communication interfaces in industrial control, telecom, and automotive auxiliary circuits.
Voltage thresholds and clamping behaviour
The reverse standoff voltage (33.3 V) is the maximum DC voltage the part can withstand without significant leakage. The minimum breakdown voltage (37.1 V) is where avalanche conduction starts. The clamping voltage (69.7 V) is the maximum voltage seen across the device when shunting the peak pulse current.
Package and mounting — DO-214AB (SMC)
The SM15T39A comes in a DO-214AB (SMC) surface-mount package, with the supplier device package also listed as SMC.
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