Selecting a Coupling Decoupling Network (CDN) for EMC testing may seem simple at first. Determine the voltage and current requirements of the equipment under test (EUT), select a compatible CDN, and begin testing.
In reality, selecting the right CDN often involves more than matching electrical ratings.
The applicable EMC standard, type of line being tested, EUT operating characteristics, current range, and whether the application uses AC, DC, or specialized power systems can all affect the appropriate test configuration.
As modern electronics continue to evolve, EMC testing applications have expanded beyond traditional electronic equipment. EV charging systems, renewable energy equipment, battery systems, DC-DC converters, railway equipment, and high-current industrial systems can all introduce additional testing considerations.
So, how do you choose the right CDN?
Start With the Test Application
Before selecting any CDN, start by understanding exactly what needs to be tested.
The applicable EMC standard should help guide the selection process. For surge testing, IEC 61000-4-5 is one of the most common standards involving Coupling Decoupling Networks, with different configurations required depending on the EUT and the lines being tested.
Start by identifying:
➡️The applicable EMC standard
➡️The required test waveform and test level
➡️The type of line being tested
➡️The number of lines requiring testing
➡️The required coupling configuration
This helps narrow the equipment options before voltage and current ratings are even considered.
The type of line is also important. CDNs are used for different applications, including power lines, data and communication lines, and signal or control lines.
A high-speed Ethernet connection, for example, can have very different testing requirements than a lower-frequency analog signal or power connection. The lines may physically look similar, but their electrical characteristics and applicable test configurations can be very different.
Voltage and Current Matter—But They Are Not the Whole Story
Voltage and current ratings are obviously important when selecting a CDN. The equipment must be capable of supporting the EUT during normal operation while EMC testing is performed.
However, selecting a CDN based solely on the highest voltage or current rating can lead to the wrong configuration.
The better question is:
What operating range and test configuration does the CDN need to support?
For example, a laboratory may test multiple products with very different current requirements. Selecting a CDN for only one EUT could limit future testing capabilities.
Modern CDN solutions are available for a broad range of applications, including conventional AC equipment, high-current industrial systems, high-voltage DC applications, and modern power electronics.
When evaluating a CDN, consider both:
✅The EUT’s current operating requirements
✅The range of products or applications you may need to test in the future
Some Full Range CDN configurations can provide greater flexibility by supporting EUTs across a broader current range, reducing the need to change equipment when testing different products.
The goal is not simply to select the largest CDN available. It is to select the configuration that properly supports the application today while providing the flexibility needed for future testing.
AC and DC Applications Can Require Different Considerations
Modern DC-powered equipment is becoming increasingly common across many industries.
Applications may include:
➡️EV and charging infrastructure
➡️Battery systems
➡️DC-DC converters
➡️Renewable energy equipment
➡️Industrial power electronics
These applications may behave differently from traditional AC-powered equipment.
Modern switching electronics and power converters can introduce characteristics that affect how the EUT responds during surge testing. Because of this, voltage and current ratings alone may not provide a complete picture of the required test setup.
The operating characteristics of the EUT should also be considered.
Certain applications may require specialized CDN configurations or additional options designed for DC systems, high-current equipment, railway applications, EV infrastructure, charging systems, or renewable energy equipment.
This is particularly important when testing modern power electronics. A CDN may appear suitable based on basic electrical ratings but require a different configuration depending on how the EUT operates and the applicable EMC standard.
Common CDN Selection Mistakes
Selecting the right CDN does not have to be complicated, but mistakes can occur when the complete application is not considered.
Common mistakes include:
❌Choosing a CDN based only on maximum current
❌Selecting equipment before identifying the applicable EMC standard
❌Ignoring how the EUT actually operates
❌Assuming AC and DC applications have identical requirements
❌Overlooking the type or number of lines being tested
❌Failing to consider specialized industry requirements
❌Selecting equipment without considering future testing needs
The goal is not to select the most powerful or complex CDN available.
The goal is to select the configuration that provides the correct coupling and decoupling solution for the required EMC test.
CDN Solutions Available
Once the testing requirements are understood, the next step is matching the application to the appropriate CDN solution.
We offer Coupling Decoupling Networks from EMC Partner for a range of power, data, communication, and specialized EMC testing applications.
Power Line CDNs
Power Line CDNs are designed for testing equipment connected to AC and DC power systems.
Available configurations can support a range of voltage and current requirements, including manual and automatic solutions, Full Range options, and specialized configurations for more demanding applications.
Depending on the application, Power Line CDN solutions can support conventional EMC testing as well as high-current equipment, high-voltage AC and DC systems, railway applications, EV and charging infrastructure, and renewable energy systems.
Best for: AC and DC power applications, industrial equipment, high-current EUTs, and specialized power systems.
Data Line CDNs
Data Line CDNs are designed for testing unshielded, unsymmetrical data, communication, signal, and control lines.
The appropriate configuration depends on factors such as the number of lines being tested and the electrical characteristics of the communication or signal connection.
HV TECHNOLOGIES offers data-line CDN solutions for applications ranging from smaller communication systems to configurations requiring multiple data lines.
Best for: Analog communication signals, signal lines, control lines, and lower-frequency digital communication applications.
High-Speed Data Line CDNs
High-speed communication applications require additional consideration because the electrical characteristics of the communication line can affect the appropriate test configuration.
High-Speed Data Line CDNs are designed for symmetrical communication applications and can support testing for technologies such as Ethernet, USB, CAN bus, and RS-485.
Different configurations are available depending on the number of lines or pairs being tested.
Best for: High-speed Ethernet and other symmetrical communication and data-line applications.
Specialized CDN Solutions
Some applications require more than a standard power or data-line CDN.
Specialized configurations are available for applications involving higher current, higher voltage, DC power systems, railway equipment, EV and charging infrastructure, DC-DC converters, and renewable energy systems.
These applications can involve unique operating characteristics and testing requirements, making it important to select a CDN configuration based on the complete test application rather than electrical ratings alone.
Best for: High-current, high-voltage, DC, railway, EV, charging, renewable energy, and other specialized EMC testing applications.
Choosing the Right CDN Starts with the Application
Voltage and current ratings are important — but they are only the beginning.
The right CDN depends on understanding the complete test application, including the applicable EMC standard, the type of line being tested, EUT operating characteristics, the current range, and whether the application involves AC, DC, or specialized power systems.
How do I choose the right CDN for EMC testing?
Start with the applicable EMC standard, required waveform and test level, type and number of lines being tested, EUT voltage and current requirements, AC or DC operation, and any specialized application requirements.
Are voltage and current ratings enough to select a CDN?
No. Voltage and current ratings are important, but the correct CDN also depends on the test configuration, type of line being tested, EUT operating characteristics, and applicable EMC standard.
What types of lines can be tested with a CDN?
CDNs are available for power lines, data and communication lines, and signal or control lines. Different line types can require different CDN configurations based on their electrical characteristics and the applicable test requirements.
Can CDNs be used for both AC and DC applications?
CDN requirements can differ between AC and DC applications. Specialized configurations may be needed for DC systems, high-current equipment, EV charging systems, renewable energy equipment, and other modern power electronics applications.
What EMC standard is commonly associated with CDN testing?
IEC 61000-4-5 is one of the common EMC standards involving Coupling Decoupling Networks for surge testing. The appropriate CDN configuration depends on the EUT and the lines being tested.
When would I need a specialized CDN?
Specialized CDN configurations may be required for high-current or high-voltage applications, DC power systems, railway equipment, EV and charging infrastructure, DC-DC converters, and renewable energy systems.