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Make Sure Your DC/DC Converters Take The Heat And Withstand Emissions in Railway Applications

When selecting a DC/DC converter for railway applications, you might think that once you’ve found the device with the right input voltage range, output power, efficiency and isolation characteristics, your job is done. However, there are other factors to keep in mind when ordering your part, which may add components to your design and affect space. Here are two conditions to consider:

Avoid Thermal Issues and RFI

DC/DC converters may play an important role within the railcar, but the operating environment is anything but hospitable to them. For instance, DC/DC converters may be subject to extreme temperatures and poor airflow aboard railcars, or those with high power densities may require additional heat removal to ensure a consistent surface temperature.

Railway applications also present many opportunities for signal disturbances that can affect the operation of various devices. This is why it’s important that DC/DC converters are tested to meet EMC (electromagnetic compatibility) standards. The International Electrotechnical Commission created the EN61000 family of EMC immunity standards for equipment subject to radio frequency emissions (RFI). They include ESD (EN61000-4-2), radiated immunity (EN61000-3) fast transients (EN61000-4-4), surges (EN61000-4-5) and conducted immunity (EN61000-4-6). In addition, EN55032 establishes EMC standards for information technology equipment. 

Go the Extra Mile With Your DC/DC Converter Manufacturer

Be sure to ask your vendor about the optimal cooling method for the DC/DC converter you choose. Polytron Devices can provide optional heat sinks to many of its power products, such as the LWB40 Series single and dual output 40-watt DC/DC converter modules with a wide 4:1 input voltage range that’s ideal for railway applications. This DC/DC converter has a 115°C over-temperature rating.

Your vendor’s datasheet also should indicate whether the converter has been tested for compliance to various EN61000 immunity standards. The LWB40 Series features a six-sided continuous metal shield which minimizes conducted and radiated noise, and it meets EN61000-4-2 through -6 — including EN61000-4-4 and EN61000-4-5 when used with the required external input components. The series also satisfies the new EN55032 requirements. While many DC/DC converters may have the specifications you seek for your railway application, consider them a starting point. Additional diligence can give you greater peace of mind.

For more information about the LWB40 Series DC/DC converters, visit the product page.


Visit the LWB40 Product Page


Railway Applications Demand DC/DC Converters That Handle a Diversity of Input Voltages

Modern railways rely on a host of electronic systems in order to operate safely and provide passenger comfort and convenience. A typical railcar distributes either 72V or 110V DC of battery power to these various systems.

Each of these systems has its own DC voltage which is often lower than the central battery voltage. Railway distributed power system designs incorporate DC/DC converters to convert the main battery voltage into the input voltage of the downstream electronic system, and DC/DC converters with a wide input voltage range can accommodate a greater number of power systems. In addition, the main battery power may also fluctuate when feeding higher power systems onboard the train, so a DC/DC converter with a wider input range is better suited to handle those wide variations in voltage.

Wide input range DC/DC converters are especially desirable for railway applications because:

  • They can accommodate a broad range of common battery and bus distribution voltages.
  • Designs can account for wide voltage tolerances and fluctuations.

DC/DC Converters Satisfy a Diversity of Railway Power Requirements

Polytron Devices offers DC/DC converters that address the diverse needs of railway power systems. For example, the OFQC60 Series 60-watt quarter-brick DC/DC converter features a wide 12:1 input voltage range covering potential distribution voltages of 9-75 V DC or 14V to 160V DC, according to the EN50155 standard. The wide input range allows the OFQC60 to accommodate many different power systems within the railway environment. Additional features and characteristics include:

  • Output voltages of 5, 12, 15, 24, 28, 48 and 53V DC.
  • Isolation voltage up to 3000V AC.
  • Efficiencies up to 92 percent.
  • EN55032 compliance.
  • Protection against over current, over voltage, under voltage, short circuits and over temperature.
  • RoHS and REACH compliance with CE Mark pending.

A Wide Input Voltage Range Means More Design Flexibility

As railways add more power systems to enable train operation and provide passenger amenities, DC/DC converters must accommodate a greater number of input voltages. Polytron Devices’ OFQC60 Series of 60-W DC/DC converters boasts an extremely wide 12:1 input range so designers can use them in a variety of power systems for modern railways.

For more information visit the OFQC60 product page


Visit the OFQC60 Product Page

EN50155 Certification Ensures DC/DC Converters Handle Multiple Railway Challenges

Railway applications present many potential uses for DC/DC converters. Electronic systems onboard modern trains for both critical systems or passenger comfort and convenience need DC/DC converters to lower the main DC battery voltage to their individual input requirements. But, all these systems in close proximity create unwanted signals that affect the safe operation of the train. They also encounter harsh environmental conditions aboard the train including shock, vibration and temperature and humidity extremes.

What is EN50155?

EN50155 is an international standard pertaining to the conditions that can impact railway operations and safety such as harsh environments or the interacting signals between multiple electrical/electronic systems. It encompasses several existing standards, such as EN50121-3-2 for EMC (electromagnetic compatibility) and EN61373 for shock and vibration. In order to attain EN50155 approval, power supplies undergo stringent testing for a host of challenging conditions. Some of the most important parameters pertaining to power supplies include:

  • Input voltage. Since trains present a diversity of bus voltages, EN50155 outlines nominal input voltages of 24, 48, 72, 96 and 110V. EN50155 sets limits for fluctuations of the rated voltage and establishes short-term deviations. The supplies must also provide an output during power interruptions.
  • EMC. With so many electronic systems populating railway vehicles, EN50121-3-2 sets strict limits to radiated emissions and ESD levels, including events like surges and fast transient bursts.
  • Shock and vibration. Not surprisingly, components inside moving rail stock will encounter frequent vibration and mechanical stresses. EN50155 establishes minimum vibration and shock requirements depending on where the device is mounted in the railway vehicle: body mounted, bogie or "truck" mounted or axle mounted.
  • Temperature and humidity. The standard provides different classes of operating temperatures for power supplies, depending on the environment. They must operate at 85 percent efficiency to reduce dissipated power that can otherwise be lost as heat, and they are required to withstand a 15-degree overtemperature at startup for 10 minutes. EN50155 also establishes humidity requirements.

Look for EN50155 Compliance

Designers that choose a DC/DC converter with EN50155 approval can be sure it will perform reliably aboard rolling stock. One example of a DC/DC converter designed especially for railway applications is Polytron Devices’ HWB Series DC/DC converters. These half-brick power supplies operate from 9-36V, 8.5-36V, 16.5-75V and 43-160V DC with no minimum load requirement, and they boast a high efficiency of up to 91 percent. The series’ EN 50155 approval also means it satisfies EN50121-3-2 (with external filter) and EN61373 for shock and vibration. Additional approvals include the EN61000-4-2, -3, -4, -5 and -6 EMC standards and UL/EN/IEC 60950-1 for safety. HWB Series converter safeguards include overvoltage, overtemperature and short-circuit protections plus heat sink options.


When selecting DC/DC converters for railway applications, look for devices that carry EN50155 certification. HWB Series DC/DC converters have been tested and approved to EN50155 so you can be sure they can both manage EMC and perform in the challenging conditions aboard rolling stock. Polytron Devices can furnish the applicable EN50155 test reports upon request.

For more information about Polytron Devices’ HWB Series DC/DC converters for railway applications, view our Railway Data Sheets.

View Our Railway Data Sheets

Remote ON/OFF Control: Remember These Basics Before Buying DC/DC Converters

PR45-24S300 v1Many DC/DC converters come with remote ON/OFF functionality to give designers a means to control the unit externally. This elementary function ordinarily appears as a bullet point on manufacturer product pages, but it helps to review this feature before checking off this requirement and moving on. Here’s a quick overview of what you should know about remote ON/OFF as you make your selection.

Some designs may not require remote control of the DC/DC converter. However, many designs require the converter to be enabled or disabled intermittently, such as in devices that only run on standby. Or, the function can turn the converter off to protect against damaging inrush currents, to name just two examples.

The Highs and Lows of Logic

When ordering, you’ll need to know the type of logic required.

  • Positive logic. Control pin logic 1 (a “high” signal) turns the converter ON, and a 0 (“low” signal) turns it OFF. If the DC/DC converter does not need outside control, a converter with positive logic uses the high signal to operate as default.
  • Negative Logic. Control pin logic is 0 (a “low” signal) turns the converter ON, and 1 (a “high” signal), turns the converter OFF. If the DC/DC converter does not need outside control, a converter with positive logic disables the converter by default.

The way you implement remote ON/OFF will vary depending on the converter and its logic. For both isolated and non-isolated converters with positive logic, the converter will operate by default with an open control pin or if the pin is connected to a high signal. If negative logic, the converter is enabled if the control pin is connected to a low level or to the negative input.

Things You’ll See On a Datasheet

Datasheets typically indicate whether remote ON/OFF control is available under the “Input” section along with the control pin’s orientation. Polytron Devices will state whether positive or negative turn-on is available, either as standard or as an option. Depending on the converter, Polytron may also show how and where ON/OFF control is referenced (for example, which secondary pin is used and if it is referenced to GND, or whether the control voltage reference is TTL- or CMOS-compatible). Other information on the datasheet may include the voltage required to enable or disable the converter as well as the input current the converter is rated to when ON and OFF. Keep in mind that some DC/DC converter implementations may need an external component to provide isolation, so be sure to check with the manufacturer when ordering.

To learn more, get in touch with our technical staff.

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​Internal Capacitors May Decide Your Power Supply’s Reliability

Internal-Capacitors-transDesigners commonly look at the MTBF (mean time between failure) ratings of power supplies to make sure they will operate reliably in an intended application. Although it can be a useful indicator, MTBF doesn’t give you the entire story about a supply’s reliability.

For instance, MTBF does not predict the power supply’s lifetime. It is the total functional life divided by the number of failures. But that expected time between failures can be longer than the life expectancy of the power supply’s internal components.

Electrolytic capacitors are usually the first components to break down inside a power supply. If the capacitor cannot reliably store energy as needed, the power supply’s reliability suffers. Several conditions can cause a capacitor to fail, so consult with your power supply manufacturer to determine how the capacitor will handle the rigors of the application environment.

Why Capacitors Fail

Some of the common reasons why capacitors fail or wear out include:

  • Voltage rating. Applying a higher voltage than the capacitor’s voltage rating can cause catastrophic failure.
  • Ripple currents. Extreme ripple currents can heat up the capacitor and dry out the electrolyte.
  • Heat. Hot operating conditions shorten the capacitor’s life. Or, the circuit board can transmit heat to cause the electrolyte to vaporize.
  • Short or open circuits. Short circuits can occur between the electrodes, and mounting errors can cause open circuits.
  • ESR. A capacitor with a higher equivalent series resistance (ESR) is less able to handle high ripple currents. High temperatures can raise a capacitor’s ESR.
  • Reduced capacitance. A capacitor’s performance can decline over time. As ESR increases, the capacitor heats up and dries the dielectric.
  • Storage life. If you expect your power supply to be inactive for long periods, remember that electrolytic capacitors have a limited storage life.
  • Other. Chemical leakage (which leads to corrosion), high leakage current, cold temperatures, capacitor size and many other factors affect the life of an electrolytic capacitor.

Internal Capacitors May Decide Your Power Supply’s Reliability

MTBF is not the only reliability metric to look at when selecting your power supply. Internal components like electrolytic capacitors have limited lifetimes, so be sure to take them into account. Capacitor lifetimes can be determined by a host of both operating and environmental factors, especially when it comes to thermal conditions.

Although it is desirable to look for built-in capacitors that offer long lifetimes in a wide range of operating environments, not all capacitors are equal: Better-quality capacitors use better-quality electrolytes. Also, be sure to get as much information as possible about the built-in electrolytic capacitor from your power supply manufacturer in order to determine whether it is appropriate for the intended application. Polytron Devices can provide the technical information, expertise and testing pertaining to internal electrolytic capacitors to help you select a power supply that will meet your expectations in the field.

To learn more, get in touch with our technical staff.

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