Improved Current Shunt Characterization Method for Core Loss Measurement

With the increasing switching frequencies and power densities in modern power converters, magnetic core losses are becoming more essential for efficiency and thermal optimization. Traditionally, the two-winding method suffers from sensitivity to phase error in practical measurements; this is mainly created by the unknown phase shift of a current-sensing resistor. Several methods have been developed to characterize the phase shift of a current shunt resistor; however, the load effects of oscilloscopes are ignored. As a result, the corresponding phase shift can be significantly underestimated. This article proposes an improved method for phase shift extraction of a current shunt to solve the problem. The effectiveness of the shunt characterization method is experimentally verified up to 50 MHz. Benefits from the proposed method, the time-consuming component tuning process is not required for core loss measurement. A measurement verification at 10 MHz shows its validity. Finally, a current shunt implemented with a coaxial resistor array is designed with a phase shift of 0.05$^\circ$ at 10 MHz and a parasitic inductance as low as 42 pH.

I. Introduction

Power converters with high efficiency and power density are increasingly pursued in modern consumer electronics. The switching frequency in a converter is then pushed to a higher range. However, a magnetic device, e.g., a transformer or an inductor, is one of the limiting factors in further improving power density. Therefore, accurate ferrite loss characterization is desired for optimizing power converters in terms of cost, form factor, and efficiency.