Investigation Of Electromagnetic Interference (EMI) Issues Of Switching Mode Power Supply(SMPS)

Switching Mode Power Supplies (SMPS) offer many advantages over linear regulators, such as high efficiency and relatively smaller size and lighting weight. However, SMPS operate at high switching frequencies, and the associated transient pulses are full of high frequency harmonics that may cause electromagnetic interference (EMI). EMI affects both the electromagnetic compatibility (EMC) performance and the cost of operation for SMPS. This dissertation examines the different kinds of EMI in typical SMPS, namely conducted (differential and common mode) and radiated interferences.The elimination of EMI in SMPS requires a systematic search for noise emissions from the converter components. To quantify the influence of the inductors on conducted EMI in SMPS, an investigation was made of conducted common mode current caused by the stray capacitance of the inductor windings in a boost converter.To minimize the post-development modification costs of SMPS, a set of rules is presented to establish a simple comprehensive model for conducted EMI in switching circuits. These rules are based on the extraction of all parasitic parameters of the layout and device modeling, including transition behavior, high frequency characteristics of the different materials, and electrostatic couplings to printed circuit board (PCB) conductors and to the ground.Anti-phase technique proposed by our research group is intended to cancel common mode noise from the generation point (drain node). To put it into practice, the influences of the parasitic capacitances have to be further investigated using a simplified equivalent circuit. Therefore, this thesis provides a detailed verification of the effects of parasitic capacitances of the anti-phase winding on the efficacy of the proposed technique.