Active Zener TVS — 1500 W peak, bidirectional
The 1.5SMC39CA/TR13: The 33.3 V reverse standoff voltage and 53.9 V clamping point place it squarely in 24 VDC rail protection — the clamp triggers well below the typical 60 V abs-max of downstream DC-DC converters and linear regulators on that bus.
Ratings that govern the fit
Breakdown voltage min 37.1 V ensures the device stays off below the nominal 33.3 V standoff, so it does not leak appreciably on a clean 24 V rail. The single bidirectional channel handles both positive and negative transients on the same line, saving a diode pair and board area compared to back-to-back unidirectional Zeners. Surface-mount DO-214AB (SMC) package is the standard footprint for 1500 W TVS diodes — the large copper pad on the cathode side sinks the pulse heat into the PCB plane.