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