Abstract
Recently, Electro-Magnetic Interference (EMI) and high frequency leakage current are grave concern for power supply authorities. Due to rapid switching of high current and high voltage, interference emission is a serious problem in many switching power circuit. However, high frequency switching is neccesary for the reduction of size and the improvement of performance of the products. Usually, EMI noise reduction is tried to accomplish by using EMI filters and shielding products. But, in many cases, those trial resulted in unsatisfactory because the analytical investigation was not performed. Recently, the analysis of high-frequency leakage currnt caused by the step change of common mode voltage produced by the PWM inverter was reported. But the other cause of high-frequency leakage current did not being made clear.
In this paper, it is clarified theoretically that the parasitic capacitor between the heat-sink and the switching semiconductor devices cause high-frequency leakage current. Furthermore, this paper shows that equalization of the parasitic capacitors and increase of the impedance for grounding the heat-sink at high-frequency range makes high-frequency leakage current reduce. Finaly, those results are verified from simulation and bread board set-up.
