?2002 Fairchild Semiconductor Corporation
? Low Start up Current
? Maximum Duty Clamp
? UVLO With Hysteresis
? Operating Frequency up to 500KHz
The UC3842/UC3843/UC3844/UC3845 are fixed
frequencycurrent-mode PWM controller. They are specially
designed for Off-Line and DC to DC converter applications
with minimum external components. These integrated
circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain
error amplifier, current sensing comparator and a high
current totempole output for driving a Power MOSFET. The
UC3842 and UC3844 have UVLO thresholds of 16V (on)
and 10V (off). The UC3843 and UC3845 are 8.5V(on) and
7.9V (off). The UC3842 and UC3843 can operate within
100% duty cycle. The UC3844 and UC3845 can operate
with 50% duty cycle.
Internal Block Diagram
* NORMALLY 8DIP/8SOP PIN NO.
* ( ) IS 14SOP PINNO.
* TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845