簡單的光開關電路,Simpleopticalswitch
IntroductionThe555isprovedtobethemostversatileandubiquitousICallovertheworld.Thisisapossibleuse:simpleinvertingschmitttrigger.CircuitexplanationWhenthephototransistorisstrokenbyIRlightitconductsandthevoltagebetweenthe1Mohmresistor(arbitrary)andthephototransdropsfromVCCtolowervalues.WhenthevoltagedropslowerthanVCC/3the555istriggeredandgoeshigh(from0TOVCC).TheamountoflightthatstrikethephototransnecessarytobringhiscollectortoVCC/3isdeterminedbytheresistor(Vdrop=Icollector*R,so,ifVdrop=2*VCC/3,theresistanceneededtosetthethresholdoncurrentisR=2*VCC/(Icollector*3)).Highsensibilityphototranswouldneedasmallerresistor,andweakerphototransistorshighervalueresistor,youcanalsouseatrimmertosettheonthresholdlevelwithprecision.Thetimeofphototransistorisn'tcritical.The555hashighcurrentcapabilityandcandrivevariousdevices,suchasBipolars,relays,bipolars+relays,mosfets,mosfets+totempole,orgivealogicoutput(seepic).Incaseyouneedtotriggersomethingwhenthegateisblocked(forexampleaburglaralarm,oramultistagecoilgun)youneedtoinverttheoutput,whichisaccomplishedusingasmallbipolartransistorwiredinaninvertingsetup(seepic)orswappingthepositionsofphototransistorwiththeresistor,sothevoltagewilldropunderVCC/3whenblocked:TheformulatodeterminetheresistancetoturnoffatIcollectorisR=VCC/(Icollector*3).
[admin via 研發互助社區 ] 簡單的光開關電路已經有2545次圍觀
http://cocdig.com/docs/show-post-34248.html
