Design of PCB Coil Based High Bandwidth Current Sensor With Power-Loop Stray Inductance Characterization

Wide bandgap devices enable design of power converters with high power density. However, these power converters require compact printed circuit board (PCB) layouts with low power-loop stray inductance. Consequently, sensing device current in such layouts with minimal intrusion in power-loop remains a challenge. This article presents a PCB coil based current sensor design featuring power-loop stray inductance characterization. The PCB coil is designed on a double pulse test (DPT) board for current sensing of a discrete TO-247 packaged silicon carbide MOSFET. The design utilizes finite element method (FEM) simulations to determine a suitable position for the PCB coil on the DPT board. The coil placement also results in an increased power-loop stray inductance, which is estimated through FEM simulations. Further, these simulations are used for computation of mutual inductance between the PCB coil and the power-loop traces. Depending on this mutual inductance, a voltage is induced across the terminals of the PCB coil, which is then integrated using an op-amp based integrator circuit. Considering practical op-amp limitations, demonstrated with LTspice simulations, various guidelines for sensor design are established in this article. A sensor prototype is developed based on these guidelines, and experimental results from its evaluation are finally presented.