Common- and Differential-Mode Separators Including the FM-Broadcasting Band

Abstract:
Noise-reduction techniques (e. g. filters) depend on the propagation mode (common mode (CM) or differential mode (DM)). Thus, the separation between CM and DM based on pre-compliance measurements is essential. A CM/DM separator is a low-cost, wide-band and non-invasive laboratory device. In converters with silicon carbide (SiC), the electromagnetic emission increases significantly at frequencies above 10 MHz. That is why conducted emission measurements, especially at frequencies above 30 MHz, are worth considering. This paper addresses the design of CM/DM separators, which also satisfy the requirements of the FM radio-broadcast frequencies up to 108 MHz. Implementation aspects covered by this work are different topologies, transformers and PCB materials. Four laboratory prototypes were constructed. The characterization of the prototypes shows that the prototypes comply with the requirements up to 110 MHz. Moreover, the CM/DM separator is validated with the help of an experimental setup using a silicon and a SiC inverter.