Component selection brief
The 1.5SMC9.1A-M3/9AT is a unidirectional TVS (transient voltage suppressor) diode built on the Zener clamping principle — the 1.5SMC family carries the TransZorb® designation, Vishay's legacy name for this Zener-based avalanche architecture. Rated 1500 W peak pulse power at a 10/1000 µs wave shape and 112 A peak pulse current, it clamps inductive transients and ESD events on a single protection channel.
Standoff, breakdown, and clamping — what the three voltage ratings mean
The reverse standoff voltage of 7.78 V is the working rail the diode watches without conduction — the circuit sees the diode as a high-impedance element in normal operation. Those two thresholds define the protection window: 7.78 V normal, 8.65 V turn-on, 13.4 V ceiling under surge. The 1500 W peak pulse rating at 10/1000 µs is a specific surge shape — shorter or faster transients (ESD, 8/20 µs lightning) will produce different peak currents and clamping levels; check the V-I characteristic curve in the Vishay datasheet for those waveforms.