UC3842B

TheUC384xBfamilyofcontrolICsprovidesthenec-essaryfeaturesto implement off-line or DC to DC fixedfrequencycurrentmodecontrolschemeswith a minimal external parts count. Internally implementedcircuitsincludea trimmedoscillatorforpre ciseDUTYCYCLECONTROLundervoltagelock- outfeaturingstart up current less than 0.5mA,aprecision reference trimmed for accuracyat the error ampinput,logictoinsurelatchedoperation,aPW comparator which also provides  currentlimit control, and a totempoleoutputstage designedto source or sinkhighpeakcurrent.Theoutputstage,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-lineapplicationsThecorrespondingthre sholds for theUC3843BandUC3845Bare8.5Vand7.9 V. The UC3842BandUC3843Bcanoperatetoduty cyclesapproaching100%.Arangeofthezeroto < 50%isobtainedbytheUC3844BandUC3845B by the addition of an internal toggleflipflopwhichblanks theoutputoffeveryotherclockcycle.