1500W peak pulse — the surge budget for a 24V rail
The STMicroelectronics SM15T27A is a 1500W TRANSIL™ TVS diode in a DO-214AB (SMC) surface-mount package. It is designed to clamp transients on a nominal 24V DC bus, with a reverse standoff voltage of 23.1V and a maximum clamping voltage of 48.3V at the peak pulse current of 207A (8/20 µs waveform).
Voltage window — standoff, breakdown, clamp
The reverse standoff voltage of 23.1V means the diode does not conduct at the normal 24V rail level, leaving the line undisturbed. Breakdown occurs at a minimum of 25.7V, and the clamping voltage is capped at 48.3V — this window ensures the protected circuit sees a transient clamped below 50V even under the full 1500W surge. The unidirectional channel is polarity-sensitive: it protects only one rail orientation, so the cathode must face the positive line.