Clamping voltage and protection margin
The 1.5SMC120CA-E3/9AT: The reverse standoff voltage is 102 V — this is the maximum DC or AC peak voltage the diode will not conduct at, so it sits across the rail without leakage under normal operation. Breakdown occurs at 114 V minimum, and clamping is specified at 165 V maximum at the rated 9.1 A peak pulse current. That 165 V clamp ceiling is the key number for the downstream components: any device rated for 200 V or more on that rail has 35 V of headroom above the clamp. If the protected circuitry uses 150 V-rated FETs or capacitors, the margin tightens — a 165 V clamp leaves only 15 V before the part's abs-max is reached, which may be acceptable for a single-event transient but not for repetitive pulsing. Bidirectional operation (one channel) means the diode clamps symmetrically on both polarities — useful for AC signal lines or bipolar DC rails where the transient can swing positive or negative relative to ground.
Operating temperature spans -65°C to +150°C junction, which covers military and industrial ambient ranges without derating the surge capability at the high end.