The UC384xA family of control ICs provides the necessary features to implement off-line or DC toDC fixed frequency current mode control schemes with a minimal external parts count. Internally im-plemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5mA,a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation,a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The Output stage, suitable for driving N-Channel MOS-FETs, is low in the off-state.Differences between members of this family are the under-voltage lockout thresholds and maxi-mum duty cycle ranges. The UC3842A andUC3844A have UVLO thresholds of 16V (on) and10V (off), ideally suited for off-line applications The Corresponding 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 by the UC3844A and UC3845A by the addition of an internal toggle flip flop which blanks the output of every other clock cycle