亮度控制小燈電路
亮度控制小燈電路--BrightnessControlforsmallLampsSwitchingoperated1.5VbulbsPortableunit,3VbatterysupplyParts:
P1________________470KLinearPotentiometerR1_________________10K1/4WResistorR2_________________47K1/4WResistor(SeeNotes)R3__________________1K51/4WResistorC1_________________22nF63VPolyesterCapacitorC2________________100΅F25VElectrolyticCapacitorD1,D2___________1N414875V150mADiodesIC1_______________7555orTS555CNCMosTimerICQ1_______________BD681100V4ANPNDarlingtonTransistorLP1_______________1.5V200mABulb(SeeNotes)SW1_______________SPSTSwitchB1__________________3V(Two1.5VAAorAAAcellsinseries,etc.)Circuitoperation:ledThisdevicewasdesignedonrequest,tocontrolthelightintensityoffourfilamentlamps(i.e.aringilluminator)forclose-uppictureswithadigitalcamera,poweredbytwoAAorAAAbatteries.Obviouslyitcanbeusedinotherways,atanyone'swill.IC1generatesa150Hzsquarewavehavingavariableduty-cycle.WhenthecursorofP1isfullyrotatedtowardsD1,theoutputpositivepulsesappearingatpin3ofIC1areverynarrow.LampLP1,drivenbyQ1,isoffasthevoltageacrossitsleadsistoolow.WhenthecursorofP1isrotatedtowardsR2,theoutputpulsesincreaseinwidth,reachingtheirmaximumamplitudewhenthepotentiometerisrotatedfullyclockwise.Inthiswaythelampreachesitsfullbrightness.Notes:LP1couldbeoneormore1.5Vbulbswiredinparallel.Maximumtotaloutputcurrentallowedisabout1A.R2limitstheoutputvoltage,measuredacrossLP1leads,to1.5V.Itsactualvalueisdependentonthetotalcurrentdrawnbythebulb(s)andshouldbesetatfullloadinordertoobtainabout1.5Vacrossthebulb(s)leadswhenP1isrotatedfullyclockwise.
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