使用Microchip的TC64X系列的线性电压风扇转速控制

PulseWidthModulation(PWM)fanspeedcontrol

methodologypulse-widthmodulatesafan’sfull-rated

powersupplyvoltageatalowfrequency,typically

30Hz.AtypicalPWMcircuit,consistingofatransistor

inserieswithafan,canbesmallandinexpensive

becauseitiseitherfullyonorcompletelyoff.Thiseffi-

cientcontrolmethodologyaffordsaverywidespeed-

controlrange(typically10%to100%offullspeed)

becausethefanmotorisexposedtoitsfull-rated

voltageduringtheactiveportionofthePWMcycle.

PWMcontrolworkswithstandard,two-wireBrushless

DC(BDC)fansofvarioussizes.However,verylarge

fans(withoperatingcurrentsof0.5Aormore)can

sometimesproduceanunwantedacousticnoisecom-

ponentwhenoperatedwithPWMcontrol.Inmost

cases,thisisremediedbyslowingtheedgesoftheout-

putswitchingtransistorwiththeadditionofasmall

capacitor.Inthemostseverecases,thismaynotbe

sufficient,whichforcestheusertoconsiderlinear

voltagespeedcontrol.MAN770LinearVoltageFanSpeedControlUsingMicrochip'sTC64XFamilyLinearvoltagespeedcontroloperatesbycontinuouslyAuthor:MicrochipTechnologyInc.varyingtheDCsupplyacrossthefan.Thelowerthevoltage,theslowerthefanoperates.Whilethismeth-INTRODUCTIONodologyeliminatestheacousticnoiseissuedescribedPulseWidthModulation(PWM)fanspeedcon