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features

· optimized for off-line and dc-to-dc the uc1842/3/4/5 family of control devices provides
converters the necessary features to implement off-line or
· low start-up current (<1 ma) dc-to-dc fixed frequency current mode control
· automatic feed forward compensation schemes with a minimal external parts count. internally implemented circuits include under-voltage
· pulse-by-pulse current limiting lockout featuring start up current less than 1 ma, a
· enhanced load response characteristics precision reference trimmed for accuracy at the error
· under-voltage lockout with hysteresis amp input, logic to insure latched operation, a pwm
comparator which also provides current limit control,
· double pulse suppression and a totem pole output stage designed to source or
· high current totem pole output sink high peak current. the output stage, suitable for
· internally trimmed bandgap reference driving n-channel mosfets, is low in the off state.
· 500-khz operation differences between members of this family are the
· low r under-voltage lockout thresholds and maximum duty o error amp
cycle ranges. the uc1842 and uc1844 have uvlo
thresholds of 16 von and 10 voff, ideally suited to
off-line applications. the corresponding thresholds
for the uc1843 and uc1845 are 8.4 v and 7.6 v.
the uc1842 and uc1843 can operate to duty cycles
approaching 100%. a range of zero to 50% is
obtained by the uc1844 and uc1845 by the addition
of an internal toggle flip flop which blanks the output
off every other clock cycle.