The UC384xA family of control ICs provides thenecessary features to implement off-line or DC toDC fixed frequency current mode control schemeswith a minimal external parts count. Internally im-plemented circuits include a trimmed oscillator forprecise DUTY CYCLE CONTROL under voltagelockout featuring start-up current less than 0.5mA,a precision reference trimmed for accuracy at theerror amp input, logic to insure latched operation,a PWM comparator which also provides currentlimit control, and a totem pole output stage de-signed to source or sink high peak current. Theoutput stage, suitable for driving N-Channel MOS-FETs, is low in the off-state.Differences between members of this family arethe under-voltage lockout thresholds and maxi-mum duty cycle ranges. The UC3842A andUC3844A have UVLO thresholds of 16V (on) and10V (off), ideally suited off-line applications Thecorresponding thresholds for the UC3843A andUC3845A are 8.5 V and 7.9V. The UC3842A andUC3843A can operate to duty cycles approaching100%. A range of the zero to < 50 % is obtained bythe UC3844A and UC3845A by the addition of aninternal toggle flip flop which blanks the output offevery other clock cycle