A Study on PCB Based Pick-up Coil for Sensing Current of A Wide Band-gap Power Semiconductor in Discrete Package

Abstract

Wideband-gap (WBG) devices are advantageous over conventional Silicon (Si) devices in their small size, low on-resistance, and high dv/dt characteristics; these ensure a high integrated density circuit configuration, high efficiency, and fast switching speed. Therefore, to diagnose and to protect a system containing a WBG power semiconductor, the transient state for accurate switch current measurement must be analyzed. As a current sensor for switch current measurement in a system comprising a surface-mount-device (SMD) type WBG power semiconductor in discrete package, the pick-up coil has the advantages of a higher degree-of-freedom configuration for its printed circuit board, a relatively small size, and lower cost than other current sensors. However, owing to the fast switching characteristics of the WBG device, a bandwidth of hundreds of MHz must be secured along with a coil configuration that must overcome the limitations of the relatively low sensitivity of the conventional current sensor. This paper proposes two Pick-up coil models as current sensors for systems, including WBG Power Semiconductor in Discrete Package. Then, for the given models, including conventional coil models, a comparative analysis of the bandwidth is performed based on the given measurement sensitivity through a mathematical method, a magnetic analysis using a finite element method, a frequency response analysis, and a simulation using PSPICE. Besides, this paper analyzes the influence of coil shape and parameters on sensor design. The ratio of mutual inductance to self-inductance values of the coil is considered performance parameter variables in the design of a sensor coil for simultaneously maintaining high bandwidth and sensor sensitivity. As for the analysis parameters, the influences on the structure of the coil and the trace and the ratio of the crossing area, the area of the magnetic flux incident surface, the distance between the coil and the trace, the number of turns of the coil, and the influence of the external magnetic flux were analyzed. The analysis process performed magnetic analysis using the finite element analysis (FEA) method and frequency response analysis to analyze the correlation with inductance, the influences of the coupling capacitance, and the magnetic field effect by the current flowing through the external trace inside the PCB. Also, the contents of numerical differences are discussed through a comparison of the results of mathematical analysis and FEA analysis. Finally, the coil model is validated and discussed through simulation and double pulse test.