随机频率调制降低开关变换器电磁干扰的研究

Research on the Reduction of EMI in Switching Converters with Random Frequency Modulation

利用随机频率调制技术从噪声产生源头上降低了开关变换器的电磁干扰。分析了具有不变概率密度分布的随机频率调制降低开关变换器EMI噪声的原理。将嵌入式系统产生的均匀分布离散随机信号加入脉宽调制芯片,开关频率随机变化,试制了一台随机频率调制开关变换器电源样机。给出了开关管电流信号的频谱以及传导干扰测试的结果。实验结果表明该技术能有效降低开关谐波峰值,使开关变换器易于通过EMI测试,具有应用前景。

How to use random frequency modulation scheme （RFMS） to reduce EMI from the noise source in switc hing converters is proposed in this paper. The principle .of suppressing EMI noise under RFMS with invariant probability density distribution is analyzed briefly. Discrete-time random signal with uniform distribution generated from embedded system is incorporated into the pulse with modulator. Thus, the switching frequency varies randomly. An experimental prototype of the fiyback converter is manufactured. The power spectral densities of the current of MOSEET and the con ducted EMI test results are presented in this paper. The experimental results demonstrated that the RFMS with prospects of application can reduce the peak level of the switching harmonics effectively and make the power converter pass the EMI test easily.