变压器电源供应器:电阻和电容
ThereareseveralwaystoconvertanACvoltageata
wallreceptacleintotheDCvoltagerequiredbya
microcontroller.Traditionally,thishasbeendonewitha
transformerandrectifiercircuit.Therearealsoswitch-
ingpowersupplysolutions,however,inapplications
thatinvolveprovidingaDCvoltagetoonlythe
microcontrollerandafewotherlow-currentdevices,
transformer-basedorswitcher-basedpowersupplies
maynotbecosteffective.Thereasonisthatthe
transformersintransformer-basedsolutions,andthe
inductor/MOSFET/controllerinswitch-basedsolutions,
areexpensiveandtakeupaconsiderableamountof
space.Thisisespeciallytrueintheappliancemarket,
wherethecostandsizeofthecomponentssurrounding
thepowersupplymaybesignificantlylessthanthecost
ofthepowersupplyalone.
Transformerlesspowersuppliesprovidealow-cost
alternativetotransformer-basedandswitcher-based
powersupplies.Thetwobasictypesoftransformerless
powersuppliesareresistiveandcapacitive.This
applicationnotewilldiscussbothwithafocusonthe
following:AN954TransformerlessPowerSupplies:ResistiveandCapacitiveAuthor:RestonConditMicrochipTechnologyInc.INTRODUCTIONThereareseveralwaystoconvertanACvoltageatawallreceptacleintotheDCvoltagerequiredbyamicrocontroller.Traditionally,thishasbeendonewithatransformerandrectifiercircuit.Therearealsoswitch-ingpowersupplysolutions,however,inapplicationsthatinvolveprovidingaDCvoltagetoonlythemicrocontrollerandafewotherlow-currentdevices,transformer-basedorswitcher-basedpowersuppliesmaynotbecosteffective.Thereasonisthatthetransformersintransformer-basedsolutions,andtheinductor/MOSFET/control