A study of EMI and switching loss reductions of unipolar and improved limited unipolar switching circuits

This paper investigates the effect of the conducted EMI (Electromagnetic Interference) and the switching loss which occurs from the switching devices in the switching period of the unipolar and limited unipolar switching circuits. The three main sources of conducted EMI and switching loss in the unipolar and limited unipolar switching circuit come from the switching devices, the number of switching times in the switching period and their switching waveform. In this paper, these three parameters are used to determine the conducted EMI which generated from the unipolar and limited unipolar switching circuits and to improve the limited unipolar switching circuit which uses the power MOSFET´s as the switching devices. The significant reduction of the conducted EMI and the switching loss can be achieved by using the controllable slope of IDS and VDS gate driver and the auxiliary current circuit respectively. The experimental results of the EMI testing according to CISPR 11, Class A and the switching loss measurement from these two circuits is also presented.