kerry2050：
PrimaryCurrentWaveformPrimarycurrentIPRIbeginstoflowwhenMosfetturnson.Transformerprimarycurrentrampstoapeakvaluedeterminedbyinputvoltage,primaryinductance,switchingfrequency,anddutycycle.Thistrapezoidal(ortriangular)currentwaveformischaracterizedinthefrequencydomainbyaspectrumwithafundamentalattheswitchingfrequencyandharmonicsdeterminedbytherelativesquarenessofthewaveformandcausesprimarilydifferentialmodeemissioncurrentstocirculatebetweentheACmainsandthepowersupplyinput.ThiscurrentwaveformcanalsocreatecommonmodeemissionsduetoradiatedmagneticfieldsifthecurrentpathdefinedbythePCboardlayoutencirclesalargephysicalarea.Mosfet導(dǎo)通時，初級電流產(chǎn)生。變壓器初級電流上升到一個峰值，該峰值由輸入電壓、初級電感、開關(guān)頻率以及占空比確定。這個不規(guī)則梯形（或者三角形）電流波形頻域特性為開關(guān)頻率的基波與諧波，它們由相關(guān)的方波形成，引起差模輻射電流在AC輸入線和電源之間循環(huán)流動。如果該電流流通面積過大，產(chǎn)生了輻射磁場，從而也會形成共模輻射。