Introduction

MEN's PU20 is a plug-in power supply unit for 19" systems (like VMEbus and CompactPCI® Serial). It is specially designed for computer systems in public transport vehicles and for harsh environments, like railway applications, making it suitable for both onboard and wayside use.

The PU20 has a nominal input power range of 24 V to 110 V with max. input voltage range of 14.6 to 156 VDC (according to EN 50155 and S-9401). It also has an automatic input voltage range detection for 24, 72, 110 VDC, to define the under-voltage level. Additionally, the PU20 has a configurable voltage range for 36, 48, 74, 96 VDC, which is controlled by a rotary switch.

The standard output voltage is 5 V with a dynamic load sharing of between 12 and 5 V with 120 W. The output power at 3.3 V is 35 W, which is shared with the 5 V load. Switch-on behaviour is independent of the load.

The PU20 also has a standby voltage of 5 V with 5W to supply the independent shelf controller and to support wake-on-LAN functionality.

The PSU provides three ports, on the secondary side, for switching the output voltages. They also indicate the event of an input power failure, output voltage failure or a fail-over temperature.

The PSU is coated conformally, and all components are secured against vibration. When more power supplies run in parallel, the performance loss is shared evenly and, in case of a fault in one of the power supplies, the output power is removed completely so as to avoid any negative effects. The double power monitoring ensures that the output voltage is within the valid range. In case of error, the voltage is powered-down as prepared by the SIL applications. The thermal stress is extremely low due to integrated heat sinks, and diversion of dissipated heat over the mounting surface.

The PU20 is fully prepared for EN 50155 compliance (March 2015), meeting all shock, vibration, EMC and isolation requirements. Operating under temperatures ranging from -40 to 70°C with increments to 85°C for 10 minutes (class TX), with hold up time of 10 ms, as is in accordance with EN 50155 Class 2.