UC3843BN HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
Description
The UC384xB family of control ICs provides the necessaryfeatures to implement off-line or DC to DCfixed frequency current mode control schemes witha minimal external parts count.
Internally implementedcircuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockoutfeaturing start-up current less than 0.5mA, a precisionreference trimmed for accuracy at the erroramp input, logic to insure latched operation, a PWMcomparator which also provides current limit control,and a totem pole output stage designed to sourceor sink high peak current. The output stage, suitablefor driving N-Channel MOSFETs, is low in the offstate.
Differences between members of this family are theunder-voltage lockout thresholds and maximum dutycycle ranges. The UC3842B and UC3844B haveUVLO thresholds of 16V (on) and 10V (off), ideallysuited off-line applications The corresponding thresholdsfor the UC3843B and UC3845B are 8.5 V and 7.9V.
The UC3842B and UC3843B can operate to dutycycles approaching 100%. A range of the zero to <50 % is obtained by the UC3844B and UC3845B bythe addition of an internal toggle flip flop which blanksthe output off every other clock cycle.
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