Common and differential mode noise separation: comparison of two different approaches

Since the EU Directive 336/89 has been published, the manufacturers of electric and electronic equipment have had to face EMC problems. For this reason, the problem of EMI measurements and the design of a proper filter in order to mitigate EMI noise have become very important. In EMI analysis, the separation of common mode and differential mode noises is a procedure well-known in textbooks. However, separated measurements are only sometimes conducted. Therefore, two different approaches are shown for the diagnosis and reduction of conducted noise emission. Two devices have been realized for determining whether the differential mode or common mode component is dominant and in order to determine whether an anticipated change in a value of an element in the power supply filter will be effective. Experimental results are given to show the validity of these approaches