Protection window and pulse rating
The 1.5KE51A-E3/73: The reverse standoff voltage is 43.6V, and breakdown occurs at 48.5V minimum; clamping is specified at 70.1V maximum when the peak pulse current reaches 21.4A. This means a 48V nominal rail sees the diode remain transparent below 43.6V, then begin conducting at breakdown, and clamp transient energy at 70.1V — well below the typical 80V abs-max of downstream 48V-input DC-DC converters.
Thermal and package fit
The DO-201AA axial leaded package (also known as DO-27) is a standard through-hole footprint; the lead length and board copper area directly affect the thermal impedance during repetitive surge events. For a single 10/1000µs pulse at 25°C, the 1500W rating is valid — derate linearly above 25°C per the datasheet curve.