Wide bandwidth, large ac current probe for power electronics and EMI measurements

Current measurements in power electronics or in EMI domains require high-performance probes. These probes must have a very wide bandwidth, be insensitive to electromagnetic interferences, and be able to measure large direct and alternating currents (ac-dc) without distortion. This paper will be limited to ac current probes. Various principles will be reviewed, in particular that based on the current transformer (CT); its limitations will be analyzed, and a solution based an a two-stage transformer will be proposed to extend low- and high-frequency performance. It will be shown that the use of new magnetic materials, such as the amorphous or the nanocrystalline, can improve large-current low-frequency operations, while preserving the smallest possible probe size. Various solutions will be provided to improve high-frequency operations. Different developments will be depicted; frequency and time-domain results will be presented.