Managing today’s complex railway communication system requires not only internal train communication networks (TCN) but also secure voice and data communication to the central infrastructure control (ground-to-train) and other trains (train-to train). GSM-based radio communication systems are mounted on trains to enable this communication.
Rolling stock equipment, such as this radio communication system, must withstand the demanding environmental, mechanical and electrical conditions defined in standards such as EN 50155.,
One challenging area is the input voltages specified in EN 50155. Trains can have a 24V, 36V, 48V, 72V, 96V or 110VDC grid, and continuous operating voltages vary between 70 % and 125 % of these nominal voltages. Addition, this standard also defines short-term voltage fluctuation around the nominal voltage of 60% for 100ms and 140% for 1s.
Let’s take a 24V system as an example. Continuous supply voltage ranges between 16.8 and 30V and can drop to 14.4V for up to 100ms or rise to 33.6V for up to 1 second. The absolute input voltage range of a 24V to 12V converter is specified from 14.4V up to 33.6V.
In case of faults such as short circuits, EN 50155 specifies the voltage to drop to zero for up to 10ms (S2 level of EN 50155) or up to 20ms (S3 level). During this time, systems have to work without interruption and the output voltage of a converter must ride through within the specified tolerances.
To cover all the different supply voltage variations in trains, the customer wanted the system to be able to work across the complete input range of down to 14.4V (60% of 24V) and up to 154V (140% of 110V).
Input Voltage Range
A further challenge includes the request to meet the reinforced isolation safety standards of EN 62368 as higher input voltages are classified as dangerous to humans.
The customer contacted RECOM for a solution, with a semi-custom converter version of a 100W railway power supply, all requirements were met. This certified converter has the necessary approvals for
railway applications and the safety approvals according to EN 62368 (replacing the legacy EN 60950 standard in 2020). Another unique feature provided by RECOM was a hold-up circuit meeting the voltage interruption requirements of EN 50155-S2. It is easy to implement and ensures that the system continues to work even during interruptions of 10ms.
The additional pin of this
semi-custom converter can be used to drive a power-good indicator at the front panel. When driving an LED, it shows whether the converter is working or not.
Next generation‘s more power-hungry radio communication system, the customer can use the
RPA200 series, that has the same electrical performance and approvals as the
RPA100 series. The standardized footprint of the half-brick format enables an existing design to upgrade its power budget for growing loads (NOTE: also requires increasing hold-up capacitance accordingly) or provide an easy leverage path for forward-looking variations.
