As power supply of electronic instruments and equipments, DC / DC converters of switching mode are so increasingly adopted that the content of high order harmonic waves in power frequency supply increases and they are restricted by International Electro-technical Commission(IEC) ( IEC ). 电子仪器和设备中的电源越来越广泛地采用开关方式的DC/DC变换器,以致于工频电源中高次谐波的含量增多,国际IEC对此作了限制。