UC1844

      The UCnamespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />1842/3/4/5 family of control ICs provides the necessary features to implement off line or DC to DC fixed frequency current mode control schemes with a minimal external parts count.Internally implemented circuits include under-voltage lockout featuring start up current less than1mA,aprecision reference trimmed for ac curacyat the error ampinput,logic to insure latched operation,a PWM comparator which also provide scurrentl imit control,and a totem poleout put stage designed to source or sink high peak current.The out put stage,suit able for driving N Channel MOSFETs,is low in the off state.

      Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges.The UC1842 and UC1844 have UVLO thresholds of 16V (on) and 10V (off),ideally suited to off-line applications.The corresponding thresholds for the UC1843 and UC1845 are 8.4V and 7.6V.The UC1842 and UC1843 can operate to duty cycles approaching 100%.A range of zero to 50% is obtained by the UC1844 and UC 1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.