Any electronic product faces a necessary hurdle before it goes to the market. It must clear the Electromagnetic Compatibility (EMC) test. This being a critical test in the design journey of an electronic product and passing this crucial test proves the design is right.
However, most designers relegate this important emissions testing to a late part of the design lifecycle of the product. This unnecessarily increases the risk of cost overruns and project delays shortly before the planned launch. Therefore, it is necessary to test for emissions at various stages of the product design plan.
When testing for EMC, you are actually minimizing the possibility of the radiated or conducted emissions from your device interfering with other electronic products nearby. Simultaneously, EMC testing ensures that the product under design is impervious to electromagnetic emissions coming from other sources in the vicinity.
Electromagnetic emissions are the energy the product emits in the radio frequency (RF) range. The device may emit these energies in either conducted or radiated form.
Below about 30 MHz, conductors and cables are not very efficient as antennas. At these frequencies, they are rather good at conducting the RF energy through shared loads and power sources. The conducted emissions, when passing through them may start interfering with other electronic equipment.
As the frequency goes up, beyond 30 MHz, conducted emissions are no longer an issue. At these high frequencies, cables and conductors start behaving more as antennas radiating the energy, thereby causing interference with other equipment.
Engineers use different test procedures and equipment for measuring conducted and radiated emissions. Although they use almost similar filter components for mitigating their effects, the electrical values involved are different.
Standards for measurement and testing electromagnetic emissions for both the conducted and radiated type differ in the US and Europe. While the US uses FCC Part 15, Europe uses CISPR 22/EN 55022. However, both approaches are very similar, and if the equipment meets the requirements of one of the standards, you can rest assured that it will meet the needs of the other standard as well.
Both the US and European standards set separate specifications for conducted and radiated emissions. The two types of emissions have their own limits applicable to the final system and its power supply.
Manufacturers making internal mountable power supplies often test them to meet regulations as standalone products. However, this is not enough if your design is using one of these power supplies with a load. In such a case, it is necessary that the complete system meet the EMC regulations. As a metal box encases the power supply, meeting the EMC challenges requires using external components.
Additionally, as most power supplies use switching topologies, they produce high levels of radiated and conducted emissions. Although the manufacturers may have already mitigated these emissions during the design phase, adding load to the power supply may produce further emissions. Therefore, it is necessary to test the combined system to ensure it meets the requirements of the EMC standards. Usually, a certified lab using calibrated test kits does the final testing. However, certain in-house testing is also possible, not requiring much equipment.