New Current Measurement Procedure Using a Conventional Rogowski Transducer for the Analysis of Switching Transients in Transistors

Developing new power converters often requires the measurement of current transients in transistors once they are positioned on its definitive location at the final printed circuit board (PCB) layout. Non-invasive conventional measuring methods such as active current probes or current transformers require a minimum space around the path of the current under measurement, but that space is not always available on definitive PCBs. The Rogowski current transducer is built by a flexible and thin coil, offers low insertion losses and a high bandwidth, so it is commonly used when space restrictions are important. New semiconductors such as SiC MOSFETs allow faster switching transients and therefore higher dv/dt occurs, leading to important perturbations on the Rogowski coil. This letter presents a two-step measurement procedure that allows the rejection of this perturbation. After a first conventional measurement, a second measurement, not encircling the current under study, is performed. During the second measurement the Rogowski coil is located close to the initial position, thus the second measurement records only the dv/dt perturbation. This perturbation can be easily subtracted to the first measurement, and therefore a perturbation-free current evolution is obtained.