Reduction of radiated electromagnetic interference in 4-phases pulse width modulation converter system

Radiated electromagnetic interference (EMI) in pulse width modulation (PWM) converter system is analyzed using discrete time Fourier series (DTFS) and a snubber circuit. The causes of radiated EMI are found through DTFS analysis of output waveform of switched voltage. By designing a snubber circuit with resistor (R) and capacitor (C) filter, overshoot and ringing of switched voltage are suppressed and the EMI is also reduced. The important factors are to minimize peak voltage and to reduce power dissipation in selecting of RC value. The design of snubber circuit is considered these points and measured EMI shows the improvement of 6 dBuV/m.

I. Introduction

When the switched-mode power supply system controls power flow using switching technology of semiconductor element, it has great merit for high efficiency, small size, and low weight. Hence it is used for almost electronic, information, wireless mobile products. The switched-mode power supply system has low power dissipation, but it must have an inductor and a capacitor, which are passive element to store energy. As the switching frequency is faster, the size of passive is smaller. Therefore, it is possible to reduce the size and weight. Therefore it is necessary to have the control circuit to regulate the output voltage in switched-mode power supply system. Fig. 1 shows the control circuit of switched-mode power supply.