低成本电动控制使用可控硅

INTRODUCTION

Mostcountertopcookingapplianceslikeelectric

ranges,skilletsandfryershaveanadjustablemechan-

icalthermostattovarytheheatoutputoftherange.

Thissolutionisinexpensive,butthereareseveral

drawbackstomechanicalthermostats:

•Mechanicalthermostatshavetobecalibratedat

thefactory.

•Theyhavepoorsimmerperformance(controlis

notpreciseatlowtemperatures).

•Theaccuracyofthesedevicesispoor.

•Mechanicalcomponentswearoutovertime.

Thisapplicationnotewilldescribealow-costmicrocon-

troller-basedreplacementforthemechanicalthermo-

statwhicheliminatesthesedrawbacks.The

PIC10F204,Microchip's6-pinPICmicro

®

microcontrol-

ler(SOT-23package),isusedtoimplementthis

solution.ThePICmicrogathersuserinputsfroma

potentiometerandcontrolscurrenttotheheating

elementviaatriac.Thisapplicationnotewilldiscuss

triactheory,soitisalsoagoodresourceforotherappli-

cationsthatinterfacetoAClines(i.e.,lightswitches,

vacuumcleanersandvariousotherhousehold

appliances).PowertothePICmicroissupplieddirectly

fromtheAClinesviaaresistivepowersupply.

Comparedtothemechanicalthermostat,the

PIC10F204solutionoffersdesignflexibility,including

theadditionofuser-friendlyfeatures.Twosuch

featuresareincorporatedintothePICmicrosolution

detailedhere.Thesefeaturesare:(1)astatusLED

indicatingtherangeisonoroff,and(2)anautomatic

shutdown.Theautomaticshutdownprovidesadded

safetybyshuttingtherangeoffafter2hoursifitisleft

unattended.AN958Low-CostElectricRangeControlUsingaTriacAuthor:RestonConditMECHANICALTHERMOSTATMicrochipTechnologyInc.OPERATIONElectricrangescreateheatbyapplyingtheAClinevoltageacrossaresistiveheatingelement.Anadjust-INTRODUCTIONablemechanicalthermostatinserieswiththeheatingelementhasarotarydialwhichsetstheamoun