Meeting radiated emissions specifications requires designers to follow a system-level design approach. Meeting EMI requirements is ultimately a systems-level issue and will depend on factors specific to the application. These include, for example, grounding architecture, the characteristics of the source, the characteristics of the load, the use of EMI shielding, mechanical attachment of the power converter to the system frame, the characteristics of the input voltage source, and distribution cabling. EMI issues typically require a very hands-on approach when bench testing because every system is different. Almost all aspects of a design can influence the EMI performance of a system. As a result, there is no single, standardized solution to this problem. This is an issue that must be addressed at the system design level.
Most systems are able to meet radiated emissions requirements by first meeting conducted emissions, using good EMI layout practices and an EMI shield. Good conducted emissions performance is often required to meet radiated emissions requirements. This is because long conductors can be an important source of radiated emissions. In addition, design features like a metal enclosure and wide power and ground planes significantly attenuate electromagnetic emissions within the radiated frequency range.
Tips on how to design your system:
Radiated emissions can result from differential and common mode conducted noise emissions. Containing these types of conducted noise emissions within a system can help improve radiated emission performance of the entire system. To determine which of the two noise emission mechanisms is prevalent in a system, please consult the “How to discern differential mode from common mode conducted emissions” Frequently Asked Question in the Conducted Emissions section of our FAQs.
Differential-Mode Radiated Emissions:
Differential-mode noise typically radiates from small loop antennas within the system. Loop antennas can be defined as the area enclosed by a current-carrying loop. The magnitude of the field is proportional to the magnitude of the current, the enclosed area, and the square of the oscillating frequency. Reducing the area enclosed by any current loop can easily minimize differential-mode noise. Care has to be taken in the layout of all SynQor power modules to reduce differential mode radiation.
Common-Mode Radiated Emissions:
Common-mode radiation is harder to control and usually determines the overall radiated emission performance of the product. Common-mode radiation usually emanates from the input and output cables. Due to their relatively long length, input and output mains are unfortunately good transmitters of EMI noise. Input and output cables behave as monopole antennas driven by a voltage. Decoupling both input and output mains with ceramic capacitors to chassis ground close to the power module suppresses the excitation voltage. Care has to be taken not to exceed the leakage current requirement when adding capacitors from any point to chassis ground.
EMI Shield:
An EMI shield is an effective technique to suppress radiated emissions generated from any component in the system. Every component lead or trace can behave as a transmitting antenna as frequencies increase. Conductors, leads, etc., can become effective antennas as their physical dimension is equal to or greater than the ½ wavelength of the radiating noise. An EMI shield (a Faraday’s cage) can be placed around the noise-emitting components to suppress radiated emissions. The enclosure needs to be made from an electrically conductive material and needs to be grounded. Ideally, it needs to be free of holes and crevices (small gaps and crevices will allow noise emissions at higher frequencies to escape/radiate into the ambient).
Any extended interfaces where two metal pieces meet can prevent the metal enclosure from suppressing radiated emissions. Generated noise with fields oriented parallel to the interfaced seam will easily circumvent the enclosure. To be an effective shield against radiated emissions, the two enclosure sections have to effectively make electrically conductive contact along the entire interface length. The shield performance can be improved by adding an EMI gasket between the two metal pieces.
If you still require support, please contact our Technical Support team to obtain help with your particular system.