In many applications involving DC/DC converters, designers face a longstanding challenge — how to deal with power interruptions. This is particularly true in railway applications where power interruptions frequently occur. In fact, the EN 50155 standard that regulates electronic equipment on rail vehicles includes requirements for ensuring output during power interruptions. This blog post will describe how advanced DC/DC converters with built-in hold-up capabilities can simplify designs while meeting EN 50155 railway requirements.
Temporary input power interruptions in railway systems are often caused by overloads at the power source or various other faults. As a result, DC/DC converters momentarily stop operating — even as briefly as 10 to 30 milliseconds — and all connected loads will lose their functions. Restarting the equipment may take several seconds to several minutes. These interruptions can be especially problematic for communication and control systems where continuous power is critical. Here's how EN 50155 classifies power interruptions:
- Class S1: Equipment must resume normal operation after any interruption.
- Class S2: Equipment must operate as normal through interruptions of up to 10 milliseconds.
- Class S3: Equipment must operate as normal through interruptions of up to 20 milliseconds.
To satisfy the EN 50155 standard, hold-up capacitors must be added with the DC/DC converter. When input interruptions occur, they can release energy they stored during normal operation as back-up power for short durations. However, these hold-up capacitors may cause a high inrush current at the moment the power is applied during a restart, which can lead to further problems. An inrush limiting circuit can address the issue, but the circuit and hold-up capacitors can take up a lot of space. And, different system voltages required for different regions means acquiring many different models of DC/DC converters and capacitors. The various DC/DC converters also involve designing different power boards and the associated inventory control plus time and effort.
Fortunately, advanced DC/DC converters can avoid the difficulties involved in meeting EN 50155 power interruption requirements, including changing power modules and considering space limitations. The HRCD20 from Daburn Electronics' Polytron Devices division features an enhanced hold-up function that provides a boosted charging voltage through a BUS pin to reduce the required hold-up capacitance for input voltages less than 80 volts. This feature provides a fixed charging voltage to allow a capacitor with the same capacitance values and rated voltage for all different supply voltages. With their ultra-wide input and their patented hold-up function, these 20-watt converters offer a single and complete unit for compliance with a variety of requirements in any region while saving development time and money.
Additional features of the HRCD20 that make it ideal for railway applications include:
- 12:1 wide input range to handle various distributed voltages and transients.
- 85% efficiency, keeping energy losses low while minimizing size and weight.
- A long list of built-in safeguards including reverse polarity, overcurrent, overvoltage, undervoltage, short circuit and overtemperature protections.
EN 50155 compliance is critical in ensuring safe and reliable electronic equipment in railway applications. When you select a DC/DC converter that effectively addresses power interruptions and inrush current — such as the HRCD20 — you will create a streamlined design that will also be well-positioned to stand up to the challenges of railway environments.
For more information, please visit our DC/DC converters page.