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MOSFET热阻测试.docx

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MeasurementofMOSFETdevicesbyboosterdevice MOSFETdevicescanbemeasuredusingthreedifferentelectricalsetups. Reversediodemeasurement Inthefirstsetupweusethereversediodeofthedeviceforheatingandmeasurementalso.ThepowerstepisappliedusingthesocalledcurrentstepmethodbyswitchingfromahigherIforce+IsensecurrentleveltoIsensemeasurementcurrentandusingtheforwardvoltageastemperaturesensitiveparameter. toT3Sterchannel Isense Iforce BothIforceandIsensecanbeprogrammedintheboosterwhichisaunipolardeviceofpositivepolarity.Thedevicevoltageistypicallybelow1V. MOSdiodemeasurement InthesecondsetupweconnecttheGatetotheDrainpinandmeasurethisthreeterminaldeviceasasocalledMOSdiode.WeapplyasimilarcurrentstepasdescribedaboveandmeasuretheforwardvoltageoftheMOSdiode. toT3Sterchannel Isense Iforce Thedevicevoltageistypically2..5Vcorrespondingtogatethresholdvoltage. Measurementwithheatingonchannelresistanceandsensingonreversediode Inthisthirdsetuptheelectricalconnectionisabitmorecomplex. toT3Sterchannel Isense Iforce UG IntheheatingphasetheUGvoltageisathighlevelensuringcontinuousheatingcurrentthroughthechannelresistanceRDSon.Thepositiveheatingcurrentcomesfromtheboosterandanegativesensecurrentisgeneratedbyanotherequipment,e.g.T3Ster. AtthestartofthecoolingIforceisswitchedoffandUGalsogoestozerothusclosingthetransistor.ThecontinuouslyflowingnegativeIsensecausesthereversediodetoopen. Thedevicevoltageistypicallylowonthechannelresistanceand-0.5Vonthereversediodeatcooling. Apracticalproblemisthattheboosteroutputisofdevicesoflargesurfaceinordertoswitchhundredamperes.Thiscancauseleakageatnegativevoltages,resultinginlossofthemeasurementcurrentfromexternalsourceandnoiseinthemeasurement. Asimple“tandem”circuitrycanstopthisleakagewhilewithstandingthecurrentlevelsofthemeasurement. toT3Sterchannel Isense Iforce UG T1 T2 DUT T1andT2aretransistorsofthesametypeandcharacteristics. T1isthedeviceundertest.T2behavesasacontrolswitchwhichisONduringheatingbutOFFduringcoolingsuchisolatingT1duringthecoolingmeasur