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Method for controlling voltage and providing temperature compensation in a thermal printer

  • US 4,113,391 A
  • Filed: 10/27/1976
  • Issued: 09/12/1978
  • Est. Priority Date: 10/27/1975
  • Status: Expired due to Term
First Claim
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1. An apparatus for controlling a thermal printer having a plurality of exothermic printing elements and adapted to be energized for printing by a current pulse produced in response to the output voltage of a power source, comprising driving circuit means for selectively applying driving pulses to said exothermic elements and control circuit means connected for detection of said power source output voltage and operatively coupled to said driving circuit means for adjusting the width of the driving pulses applied to said exothermic printing elements in response to the level of said power source output voltage so that the width of said driving pulses is increased in response to a decrease in said output voltage and is decreased in response to an increase in said output voltage, said control circuit means including a pulse generation circuit operably couplable to receive said power source output voltage for producing an oscillatory signal, said pulse generation circuit including voltage sensitive means including a varistor independent of said plurality of exothermic elements for adjusting the period of said oscillatory signal in response to the level of said output voltage so that the period of said oscillatory circuit is increased in response to a decrease in said output voltage and decreased in response to an increase in said output voltage, said oscillatory signal being applied to said driving circuit means for determining the width of said driving pulses.

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