UC2843B

TheUC384xBfamilyofcontrolICsprovidesthenecessaryfeaturesto implement off-line or DC to DC fixedfrequencycurrent modecontrolschemeswith a minimal external parts count. Internally implementedcircuitsinclude a trimmed oscilla -torforpreciseDUTYCYCLECONTROLundervoltagelockoutfeaturingstart-upcurrentlessthan0.5mA,aprecision reference trimmed for accuracyat the error ampinput,logictoinsurelatchedoperation,aPWM comparator which alsop rovide scurrentlimitcontrol, and a totempoleoutputstage designedto source or sinkhigh peakcurrent. The output    stage, suitable for driving N-Channel MOSFETs, is low in the offstate.
Differencesbetweenmembersofthisfamilyarethe under-voltagelockoutthresholdsandmaximumduty cycle ranges. The UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff lineapplications The correspondingth resh- oldsfortheUC3843BandUC3845Bare8.5Vand7.9 V.TheUC3842BandUC3843Bcanoperatetoduty
cyclesapproaching100%.Arangeofthezeroto < 50%isobtainedbytheUC3844BandUC3845Bby thea ddition of anintern altoggleflipflopwhichblanks theoutputoffeveryotherclockcycle.