The 3U 12HP power supply unit PU1 is a plug-in device for 19" systems (e.g. VMEbus, CompactPCI®) and is especially designed for railway computer systems, being fully compliant with EN 50155. The 1.5 kV (effective) optically isolated PSU comes with a nominal input voltage of 110 VDC with a wide input range of 77..137.5 V (max. input voltage range 66..154 V according to EN50155) and a single output of 5 V at 75 W. It works up to +85°C without derating, delivering a thermal warning at over-temperature and switching off at +95°C. The PSU supports an error signal (5 ms hold-up time), reverse-connect protection, permanent short-circuit protection, voltage control, synchronization, voltage in fail (ViF) and voltage out fail (VoF) as well as remote on/off. The subassembly is immersion-painted und partially cast, and components are secured against vibration. The thermal stress is extremely low due to integrated heat sinks and diversion of dissipated heat over the mounting surface.