DCRIPTION
The UC384xB family of control ICs provid the necsary
featur to implement off-line or DC to DC
fixed frequency current mode control schem with
a minimal external parts count. Internally implemented
circuits include a trimmed oscillator for precise
DUTY CYCLE CONTROL under voltage lockout
featuring start-up current ls than 0.5mA, a precision
reference trimmed for accuracy at the error
amp input, logic to insure latched operation, a PWM
comparator which also provid current limit control,
and a totem pole output stage digned to source
or sink high peak current. The output stage, suitable
for driving N-Channel MOSFETs, is low in the offstate.
Differenc between members of this family are the
under-voltage lockout thrholds and maximum duty
cycle rang. The UC3842B and UC384 have
UVLO thrholds of 16V (on) and 10V (off), ideally
suited off-line applications The corrponding thrholds
for the UC3843B and UC3845B are 8.5 V and 7.9
V. The UC3842B and UC3843B can operate to duty
cycl approaching 100%. A range of the zero to <
50 % is obtained by the UC384 and UC3845B by
the addition of an internal toggle flip flop which blanks
the output off every other clock cycle.