1500W peak pulse power — what it buys the 24V rail
The STMicroelectronics SM15T30A is a unidirectional TRANSIL™ TVS diode in the SM15T series, rated for 1500W peak pulse power (10/1000µs waveform). With a 25.6V reverse standoff voltage and a minimum breakdown of 28.5V, it sits right on the 24V nominal rail — the 28.5V clamp threshold gives margin above the 24V steady-state while the 53.5V clamping at 187A (8/20µs) catches surges from inductive loads or line transients. The DO-214AB SMC package handles the 1.5 kW pulse without exceeding the 150°C junction limit, and the surface-mount footprint keeps assembly in the same reflow pass as the rest of the board.
Breakdown and clamping — the 24V system fit
For a 24V DC bus, the 25.6V reverse standoff means the diode stays off during normal operation. The 28.5V minimum breakdown ensures the avalanche triggers before the downstream regulator's absolute maximum is hit — typical 24V supplies have a 30-36V transient tolerance, so the 53.5V clamp at 187A (8/20µs) catches the surge before it propagates. No power line protection is built in (the part is a standalone clamp), so place it directly across the input terminals with short traces to the bus.