kerry2050：
PrimaryCurrentWaveformPrimarycurrentIPRIbeginstoflowwhenMosfetturnson.Transformerprimarycurrentrampstoapeakvaluedeterminedbyinputvoltage,primaryinductance,switchingfrequency,anddutycycle.Thistrapezoidal(ortriangular)currentwaveformischaracterizedinthefrequencydomainbyaspectrumwithafundamentalattheswitchingfrequencyandharmonicsdeterminedbytherelativesquarenessofthewaveformandcausesprimarilydifferentialmodeemissioncurrentstocirculatebetweentheACmainsandthepowersupplyinput.ThiscurrentwaveformcanalsocreatecommonmodeemissionsduetoradiatedmagneticfieldsifthecurrentpathdefinedbythePCboardlayoutencirclesalargephysicalarea.Mosfet导通时，初级电流产生。变压器初级电流上升到一个峰值，该峰值由输入电压、初级电感、开关频率以及占空比确定。这个不规则梯形（或者三角形）电流波形频域特性为开关频率的基波与谐波，它们由相关的方波形成，引起差模辐射电流在AC输入线和电源之间循环流动。如果该电流流通面积过大，产生了辐射磁场，从而也会形成共模辐射。