(Published in PCIM Magazine, July 1999)
Rafik Stepanian, LCR Electronics, Norristown PA
Power Products (power supplies, inverters, etc.), utilizing high frequency switching components are more efficient, smaller and more cost-effective than in years past. Unfortunately, a major trade-off to the high frequency switching is the ability of these Power Products to generate very high levels of unwanted Electromagnetic Interference (EMI) into the power line. The FCC in the US and the European Commission (EC) in Europe has stringent specifications dictating the allowable levels of EMI these products may produce. The EC also has regulations concerning the susceptibility of electrical products to ambient levels of interference.
Power Line Filters can be installed at the input of these electronic systems to limit the levels of EMI conducted along the power cord into the supply system. These Filters are designed to reduce the conducted and radiated EMI (both common-mode and differential-mode) to acceptable limits so that they comply with these National and International regulations. The filter components (capacitors and inductors), methods of construction, values and the number of sections are selected to provide the required attenuation.
Suppressing EMI is not as simple as selecting an off-the-shelf filter from a catalog. The product has to be tested to the relevant standards (FCC, CE, VDE, etc.) and a filter designed to meet those standards in a cost-effective manner. Once the filter is designed it can be incorporated in the electronic system.
To avoid undue EMI Filtering costs, designers should consider EMI prevention at the start of a product’s design phase. EMI friendly components and good EMC practices should be used during the pc board design phase. These practices include using multi layer boards, minimizing trace lengths and sharp corners, avoiding ground loops, using de-coupling capacitors, etc. These practices will provide for a more economical filter solution.
Experience has shown that the earlier EMI is considered the less expensive the final EMI solution. Also, because EMI is not a core competency in most companies, it should be out-sourced to a company that not only has the capability of testing but more importantly has the ability to design an economical EMI solution into the final product. This will allow the product to be presented for final approval without the need for re-testing or any EMI surprises. Remember that a product-specific filter solution will be less costly in the long run than an off-the-shelf filter.
For More Information Contact:
Ron Minicucci
LCR Electronics, Inc
9 South Forest Ave, Norristown, PA 19401
Tel: 1-800-527-4368
FAX: 1-610-278-0935
Internet: sales@lcr-inc.com