Resumen de Characteristic analysis of switching voltage power spectra under the mode of random carrier‐frequency modulation
Haiyan Guo, Zhaoji Li, Zhang Bo
Purpose – The purpose of this paper is to provide a theoretical platform for studying the characteristic of random carrier frequency (RCF) modulation and analyze the related parameters in terms of electromagnetic interference (EMI) suppressing.
Design/methodology/approach – In this paper, the expression of the amplitude of switching voltage power spectra under the RCF mode is presented. According to the expression, the effectiveness of related parameters on EMI mitigation is discussed. Theoretical predictions are confirmed with a closed‐loop boost converter which power is 7.5 W and nominal switching frequency is 200 KHz. Finally, special attention has been paid to output voltage ripple.
Findings – Under RCF scheme, with increasing of random degree, the spectrum of switching voltage is dispersed, so the power spectrum density amplitude of switching voltage falls, and then the level of EMI is lowered. This theory shows that the voltage power spectrum density attains maximum when d=0.5, so in the spread spectrum modulation, the duty cycle of 0.5 should be avoided in terms of conducted EMI mitigation.
Originality/value – The analytical expression of switching voltage power spectra under the RCF mode is presented, providing a theoretical platform for the related research. The selection of duty cycle has effect on EMI level is put forward for the first time. Voltage ripple is discussed in close‐loop circuit.
