Methodology for Extracting Low-Frequency Input Impedance of Personal Computer During Operation Using Dual Current Probes Method

This article proposes a measurement methodology for extracting input impedance while operating a power device such as a personal computer (PC). Electronic devices such as switched-mode power supply in PC may have different impedances depending on operating conditions. So, the effect of external noise during operation can be predicted through impedance extraction. Since it uses a type of inductive coupling, the conventional method of extracting impedance during operation using current probes makes measurement challenging at low frequencies because the signal is attenuated due to the decrease in induced voltage when the frequency decreases. As a solution, this article proposes a methodology that amplifies the signal by increasing the number of turns on the probes. Using the proposed methodology, it is possible to extract the impedance of a power device by adjusting the number of turns according to the frequency. Calculation of the number of turns appropriate for an increased signal was verified through experiments. The proposed methodology makes it possible to extract the impedance of a device during operation over broadband, from 20 kHz to 100 MHz. It can be applied for various fields, such as electromagnetic pulse protection and electromagnetic interference filter design in the future.