The 1.5SMCJ17A is a unidirectional Zener-based TVS diode rated 1500 W peak pulse at the standard 10/1000 µs waveform — the workhorse surge shape in IEC 61000-4-5 immunity testing. At that pulse width, a 54.3 A peak current flows into the clamp, and the diode holds the downstream node to 27.6 V maximum. That headroom above the 17 V standoff is what absorbs the transient energy and shunts it away from the protected circuitry. The minimum breakdown of 18.9 V sits about 11 % above the 17 V standoff — the diode stays off during normal operation and turns on sharply once the transient exceeds that threshold. For a 24 V nominal rail, this 17 V standoff part keeps leakage current negligible until a surge event forces it into conduction. This is not a power-line protection device — the listing flags Power Line Protection as No. It is suited for board-level protection on control, signal, or secondary power rails, not for AC line-front protection where a higher-energy device class is required.
SMC package and junction temperature for board-level deployment
Verify the temperature coefficient in the Diotec datasheet if the circuit sees sub-zero ambient.