6. REGULATIONS
Generally, electronic equipment must comply with a series of standards, both for electromagnetic compatibility and safety, which within Europe are certified by the CE identification.

6.1 Electromagnetic compatibility (EMC)
From January, 1st, 1996, full compliance with the European Directive for Electromagnetic Compatibility 89/336/EEC is compulsory. This regulation imposes a reduction of the radiated and conductive noise level to acceptable values and requires equipment to be immune in environments with certain radiation levels and external noise input through the mains terminals. This Directive is broken down in three standards: basic, generic and product-specific. The basic standard establishes test methods, the product standard is applies to specific product classes and the generic standard applies to all kinds of equipment in an electromagnetic environment which is not covered in the product-specific standard. Generic and product-specific standards refer to the basic standard to carry out the test used to work out the compliance statement. A first division can be made between aspects referring to emission (radiated and conducted) and to susceptibility (radiated, conducted and discharged). The table below shows the three types of standards published in February 1996. As a manufacturer, it is your responsibility to choos e the standard your products will have to meet.

6.1.1 Conducted noise
Switched-mode power supplies, because of their nature, can be a radio-frequency interference source. There are two basic interferences or noise types: conducted or radiated. Within the conducted noise, two modes can be distinguished: Differential mode which mode is encountered between the line poles, and common mode; this is the one encountered between ground and any of the line poles. Filters are used to reduce noise to acceptable levels. Fig. 36 shows two types of filters, the PI FILTER which is appropriate to reduce noise in differential mode and the COUPLED FILTER which is appropriate to reduce noise in common mode. Noise in common mode is harmful and, therefore, limited by standards. Voltage limits generated by a piece of equipment can be found in standards such as EN50081-1 or EN50081-2, depending on the environment type in which the equipment is supposed to operate. CISPR limits A and B can be seen in the following figure: CISPR A and B graphs.

6.1.2 Radiated noise
There are also maximum electromagnetic radiation limits, (mainly due to the switching of high voltage and high current peaks produced by all power supplies) that can be found in the EN50081-1-2 generic standards. Both in radiated as well as conducted noise, these standards refer to basic standards and are used as a generic reference to product specific standard.