型號： UC3842
廠商： STMicroelectronics

標準：
分類： 半導體
描述： currentmodepwmcontroller
OPTIMIZED FOR OFF-LINE AND DC TO DC
.CONVERTERS .LOWSTART-UP CURRENT (< 1 mA) AUTOMATIC FEED FORWARD COMPENSA.
TION .PULSE-BY-PULSECURRENT LIMITING ENHANCED LOAD RESPONSE CHARAC.
TERISTICS UNDER-VOLTAGELOCKOUTWITHHYSTER.
ESIS .DOUBLE PULSE SUPPRESSION .HIGH CURRENT TOTEMPOLEOUTPUT INTERNALLY TRIMMED BANDGAP REFER.
ENCE .500 KHz OPERATION LOWRO ERRORAMP
DESCRIPTION
TheUC3842/3/4/5family of controlICs providesthe
necessary features to implement off-line or DC to
DC fixed frequency current mode controlschemes
witha minimal externalparts count.Internallyimplementedcircuitsincludeundervoltagelockout
featuring
start-up current less than 1 mA, a precision reference
trimmed for accuracy at the erroramp input,
logic to insure latched operation, a PWMcomparatorwhichalso
providescurrentlimit control,anda totem
pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-ChannelMOSFETs, is low in theoff-state.
Differencesbetweenmembers of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The UC3842 and UC3844 have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding
thresholds for the UC3843 and UC3845 are 8.5 V
and 7.9 V. The UC3842 and UC3843 can operate
to duty cycles approaching 100%. A range of the
zero to < 50 % is obtained by the UC3844 and
UC3845by the additionof aninternal toggleflip flop
which blanks the output off every other clock cycle.
UC3842

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