数字式恒流LED驱动器

ThisdocumentdescribesapowerLEDdriversolution

usingthePIC12HV615microcontroller(MCU).The

PIC12HV615isan8-pinMCUwithmanyintegrated

analogfeatures.TheLEDdrivercircuitisabuck(step-

down)solutionandthecircuitpresentedherecan

operatefrommostanyinputvoltagesourceaslongas

itexceedstheforwardvoltageoftheLEDstobedriven.

Aproportional-integral(PI)controlleralgorithmisused

toregulatetheLEDcurrenttoaconstantvalue.ThePI

controllerisexecutedatarateof976Hz,leavingplenty

ofCPUtimeavailableforothertasks.Althoughthis

sampleratewouldprovideinadequatecontrol

responseformostpowersupplyapplications,itworks

wellforLEDapplicationsbecausetheLEDpresentsa

constantloadtothepowerstage.Therefore,the

controllerdoesnotneedtomakefrequentadjustments.

TheLEDcurrentissampledusingaresistorinseries

withthesourceoftheMOSFETinthebuckcircuitand

amplifiedusingasingleopamp.TheLEDcurrentis

sampledusingoneoftheavailableADCinputsonthe

PIC12HV615.TheEnhancedCaptureComparePWM

(ECCP)moduleoftheMCUisusedinPWMmodeto

drivethebuckcircuit.SincetheMCUhasaninternal

voltageregulatorand8MHzoscillator,veryfew

externalcomponentsarerequiredtocompletethe

circuit.AN1138ADigitalConstantCurrentPowerLEDDriverdrivecurrentforthistypeofLEDwouldbe350mAandAuthor:StephenBowlingatypicalforwardvoltagewouldbe3.5V.Secondly,weMicrochipTechnologyInc.willassumethatthecircuitinputvoltageis12V.Theinductorvaluewillbechosentoallowamaximumcurrentrippleof+/-20%.TheeyewillnotbeabletoINTRODUCTIONperceivethiscur