1500 W peak pulse — clamping a 49 A surge
The 1.5SMC22A-E3/9AT: The 1.5SMC22A-/9AT is a unidirectional Zener TVS from Vishay's 1.5SMC TransZorb series, rated for 1500 W peak pulse power at 10/1000 µs. That 1500 W rating means it can clamp a 49 A surge (Ipp) to 30.6 V without failing — the energy is absorbed in the silicon junction, not passed downstream to the protected load.
Standoff, breakdown, and clamp — the three voltages that matter
Reverse standoff is 18.8 V — the rail voltage this diode sits across without conducting. Breakdown triggers at 20.9 V minimum, and clamping maxes at 30.6 V at the full 49 A pulse. The gap between standoff and clamp (12 V) is the protection window; a 24 V bus sees no leakage at nominal, but a transient above 20.9 V gets shunted hard. The DO-214AB (SMC) package handles the 1500 W pulse without exceeding the die temperature limit, provided the PCB copper area under the cathode tab is adequate for heat sinking.