AEC-Q101 grade — no substitute for the audit trail
The SM30T47AY is a Zener diode from STMicroelectronics' SM30TY TRANSIL™ series, explicitly qualified to AEC-Q101 and marked for automotive applications. That qualification means the part comes with a PPAP-ready data package — the OEM auditor will ask for it, and this part has it. The 3000W peak pulse power rating (10/1000µs waveform) handles the 40V reverse standoff rail, clamping transients at 64.5V maximum while conducting 43.5A peak pulse current. Junction temperature spans -55°C to 175°C, comfortably covering under-hood and engine-bay thermal profiles.
Breakdown and clamping — the numbers that decide fit
Minimum breakdown voltage is 44.4V, with a typical 40V reverse standoff voltage. That 4.4V margin between standoff and breakdown is the window the designer works with — the rail must stay under 40V during normal operation, and the part starts conducting above 44.4V. Clamping is specified at 64.5V maximum at the rated 43.5A peak pulse current. For a 3000W device in a DO-214AB SMC package, this clamping voltage is consistent with a 40V-class automotive TVS used for load-dump and ISO 7637-2 pulse 5a protection.