New-Tech Europe | Sep 2017 | Digital Edition

Considering EMC Emissions Early in the Design Process

Bruce Rose, Applications Engineer, CUI

One of the design activities often left to the end of a project is verifying that the product meets electro-magnetic compatibility (EMC) emissions requirements. EMC regulations help to ensure unintentional electro- magnetic conducted and radiated emissions do not interfere with other electronic devices. While delaying EMC compliance testing until the end of the project is a common practice, unexpected costs and project delays can be avoided by considering EMC compliance earlier in the design process. Electro-magnetic conducted and radiated emissions are the radio frequency (RF) energy emitted by a product. The level of RF emissions are regulated to ensure they do not cause unreasonable harm to other electronic products. At low frequencies (less than about 30 MHz) the conductors and cables of most electronic devices are ineffective

as antennas and thus radiated emissions are not an issue. At these low frequencies the conductors and cables can conduct RF energy through shared power sources or loads and cause issues with other electronic products, while at high frequencies (above about 30 MHz) the impedances of the conductors and cables attenuate the conducted energy sufficiently to prevent it from being an issue. However, at these higher frequencies the conductors and cables can serve as antennas and radiate the RF energy with the ability to cause interference with nearby electronic products. Most industrial and consumer electronic products sold in the United States are required to meet conducted and radiated emissions standards as described in FCC regulations Title 47 Part 15, often referred to as FCC Part 15. Similar standards for products sold in

Europe are governed by European regulations CISPR 22/EN 55022. Both sets of these regulations describe limits for conducted and radiated emissions and are applied to the final system, including the internal or external power supply. While these two sets of regulations are created and administered by separate organizations they have been constructed to be similar or “harmonized”. One benefit of harmonizing these regulations is that designing a product to meet one set of regulations typically ensures it will also satisfy the requirements set forth in the other set of regulations. Conducted radiation specifications cover emissions in the frequency range of 150 kHz through 30 MHz. A separate set of radiated emissions specifications covers the spectrum of 30 MHz and greater. Test procedures and tools are slightly different for conducted versus radiated

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