UC 3842 IC

INTRODUCTION

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. 

FEATURES: 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.

APPLICATIONS: 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.

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