kerry2050：
PrimaryCurrentWaveformPrimarycurrentIPRIbeginstoflowwhenMosfetturnson.Transformerprimarycurrentrampstoapeakvaluedeterminedbyinputvoltage,primaryinductance,switchingfrequency,anddutycycle.Thistrapezoidal(ortriangular)currentwaveformischaracterizedinthefrequencydomainbyaspectrumwithafundamentalattheswitchingfrequencyandharmonicsdeterminedbytherelativesquarenessofthewaveformandcausesprimarilydifferentialmodeemissioncurrentstocirculatebetweentheACmainsandthepowersupplyinput.ThiscurrentwaveformcanalsocreatecommonmodeemissionsduetoradiatedmagneticfieldsifthecurrentpathdefinedbythePCboardlayoutencirclesalargephysicalarea.Mosfet導(dǎo)通時(shí)，初級(jí)電流產(chǎn)生。變壓器初級(jí)電流上升到一個(gè)峰值，該峰值由輸入電壓、初級(jí)電感、開(kāi)關(guān)頻率以及占空比確定。這個(gè)不規(guī)則梯形（或者三角形）電流波形頻域特性為開(kāi)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(dòng)。如果該電流流通面積過(guò)大，產(chǎn)生了輻射磁場(chǎng)，從而也會(huì)形成共模輻射。