UC 3842 IC


The UC3842/3/4/5 family of control ICs provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal 
external parts count. Internally implemented circuits include under voltage lockout featuring start-up current less than 1 mA, a precision reference trimmed for accuracy at the erroramp 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-ChannelMOSFETs, islow in theoff-state.  The figure with Pin-Configuration of UC3842 is shown below.

Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications. The corresponding thresholds for the UC3843 and UC3845 are 8.5 V and 7.9 V. The UC3842 and UC3843 can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844 and UC3845by the additionof aninternaltoggleflip flop which blanks the output off every other clock cycle. 


This IC is very useful because of low power consumption and usability at high temperatures. Some of its silent features are listed below.  

  • Low power dissipation,
  • Optimized for off-line and dc to dc converters
  • Low start-up current (< 1 ma). 
  • Automatic feed forward compensation.
  •  Pulse-by-Pulse current limiting.
  •  Enhanced load response characteristics.
  •  Under-Voltage locks out with hysteresis.
  •  Double pulse suppression. 
  •  High current totem pole output.
  •  Internally trimmed band gap reference. 
  •  500 kHz operation. 


It is used to invert the input supply given to it. Due to this feature it can be used in various circuits. Some of its well known applications are listed below.

  •  Wave and pulse shapers.
  •  Astable multivibrators.
  •  Monostable multivibrators.



Who's new

  • ravirajpatil871...
  • shubhambajoria
  • yassir
  • demiholyman890954
  • scottgillum51169040

Get Notified



We are Social


Subscribe to Syndicate