Tutorial

7/27/2015 UnregulatedPowerSupplyTutorialSparkFunElectronics
https://www.sparkfun.com/tutorials/103 5/9
Sotheloadattachedtothepowersupplyallowscurrenttoflow,whichinturncreatesavoltagedropin
sideofthepowersupplyduetocopperlossesandironlossesonthetransformer.
Ripple
Letsstartwithwhatthecapacitordoesandhowitaffectsrippleintheoutput,asthisisthefirstlineof
defensefromACaftertherectificationofthesteppeddownACsignal.Therectifiedsignalwithoutthe
capacitorwillideallylooklikethis:
Inthepowersupplyshowninthistutorial,thereisonlyonefiltercapacitorof470uF.Thefiltercapacitor
opposeschangesinvoltageandwillsmoothoutthebumpsintherectifiedsignal,toacertainextent.A
capacitorthatwillsmooththesignalwilldischargeandchargealmostasfastaseach180degreephase
(eachintegeraboverepresentsa180degreesofasinewave)oftherectifiedpulse.Soyouwillgeta
signalthatwilllookmoreorlesslikethis:
Thebumpsinthenowsemifilteredsignalarecalledripple.
Asthesignalisinitspositivecycle(indicatedby'a')above,thecapacitorischargingthroughtheseries
combinationofhalfofthesecondarycoilandoneofthediodes.Thesmallertheinternalresistanceof
thepowersupplythefasterthecapwillcharge.
Thedischargeofthecapacitorandslopeoftheline(indicatedby'b')above,willdependonthevalueof
capacitorandtheresistanceoftheloadyouhaveattachedtothesupply.Duringthiscycle,thediodeis
reversedbiased(nocurrentwillflow)andthecapacitorwillonlydischargethroughtheloadresistor.The
largertheresistanceoftheload,thesmallertheloadcurrent,andtheslowerthedischargeofthecap.If
youlookatthechartabove,youwillseediminishingripplewithincreasingresistance.
Hereiswhattheactualripplelookslikeonthesignalwitha20Ohmloadresistor.