The SM15T27AY is a unidirectional Zener TVS diode from STMicroelectronics, rated for 1500W peak pulse power (10/1000µs waveform). The device protects a 23.1V nominal rail, with a minimum breakdown voltage of 25.7V and a clamping voltage of 48.3V at the peak pulse current of 207A (8/20µs).
Voltage ratings — what they mean for rail protection
The 23.1V reverse standoff voltage is the maximum continuous DC voltage the TVS can withstand without conducting. For a 24V nominal automotive bus (which can ride up to 28V during load dump or alternator surge), this part sits below the rail — the 25.7V minimum breakdown gives a narrow but workable margin. The 48.3V clamp is the voltage the protected circuit sees during a surge; downstream components must survive that peak for the pulse duration.
Package and footprint
Housed in a SMC package, surface-mount. The SMC body is larger than the smaller SMA/SMB siblings, sized to dissipate the 1500W pulse without exceeding the 150°C junction limit.
Lifecycle and sourcing posture
Listed as Active by STMicroelectronics. For production BOM lines requiring AEC-Q101 protection on a 24V nominal rail, this part is a current-design-in candidate.