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

Abstract

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.