Finding ‘Ready to Use’ DC/DCs for Mobility and Rail Applications

This article by RECOM Power discusses what specifications a true ‘ready to use’ product needs to meet. Mobility applications put heavy demands on power converters. While commercial products may meet some of the required specifications, extensive external circuitry is typically required for overall compliance with standards such as EN 50155 for railways.
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Of all the environments for electronic equipment, mobile ones are perhaps the most severe. But it is a growing market across all sectors, from railways to materials handling equipment, EVs to e-scooters, and much more. In rail rolling stock applications particularly, automation is being increasingly incorporated for safety and efficiency savings, along with convenience features such as data connectivity and intelligent signage. All of this must operate reliably in the typical rail environment of high pollution, shock, and vibration with power most often from the traditional DC rail of 110 VDC nominal, with some global variations down to 24 VDC.
The standard that typically applies is EN 50155, currently version July 2021, which defines the electrical and physical environment and technical construction features, reliability, maintenance, service life, documentation, and testing.

Rail supply voltages vary widely

As well as meeting environmental, isolation, and EMC specifications, the power supply modules that convert the DC supply to a clean rail for the sensitive electronics must cope with wide variations in input voltage, which also has superimposed surges, dips, and drop-outs.
Figure 1 shows the levels defined in EN 50155 for no impact on performance.
Figure 1: The variations in nominal DC supply rail voltage according to EN 50155 for no impact on performance
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