Although not visible to the passengers, modern trains need a lot of electronic equipment to comply with increased safety and communication requirements, which enables them to handle numerous complex functions within the train control systems easily, as well as offer more comfort and information to the passengers. This requires increased computing power, more sensors, and higher communication transmission speed, all of which results in increased demand for power from the power suppliers. However, space is limited, and the mechanical construction of a train cannot be changed easily. Quite often, new systems are required to fit into the existing small space allocated to a significantly less powerful legacy system designed years ago.
A customer faced the above challenge while upgrading an existing central computing unit by adding a more powerful CPU and additional interfaces to the system. The old system required 40W of power, where as the new unit needed 60W; in addition to this, it required more space on the PCB to accommodate additional powerful, interfaces. Increasing the power by 50% also means more heat and thermal stress in the system, although the operating temperature limit (+75 °C) remained the same. Optimized thermal management, in conjunction with a reduction of dissipated losses in the power system, became important factors.
The customer also wanted the system to work seamlessly across all the different train voltages from 72 to 110V nominal (40 to 160V continuous operation with EN 50155 compliance) with a protection against the high transients defined in
RIA12 and NF F01-510 of up to 385VDC. The legacy power system was not able to deliver 60W without taking more space on the board, and losses in the conversation stage would have been prohibitive for the new design.
With a tiny 60W converter and a transient protection module from RECOM, it was possible to address all these challenges. The converter was even smaller than the previous 40W unit, which freed up space for additional interfaces, and the modern, highly-efficient technology of the converter helped to reduce losses significantly. This converter uses a baseplate for cooling, so, it was possible to move the heat out of the system and onto the chassis of the computing unit.
In addition, the small transient protection module took up less space than the previous discrete solution and ensured that the downstream, 90W
DC/DC converter is protected against the high transients of the train grids. The final challenge was the high-isolation barrier of 6kV requested for the 5V interface supplies. RECOM solved this as well with small 2W converters which offered this isolation.
For a lower power solution, the customer can use a 40W sister part with the same qualification data but reduced maximum power and output current.
