Thermal printer head having current sensors connected to heating elements

A thermal printer head comprising:

• an array of heating elements mounted on an insulating base member, each of the heating elements being connected to a common voltage source and having a temperature dependent electrical resistance;
• a plurality of electrically resistive elements connected in series with said heating elements, respectively, to form a plurality of series circuits;
• a plurality of current supply means corresponding respectively to said resistive elements for selectively supplying a current to said series circuits in response to a sequence of print signals;
• and
• control means for making a determination whether a voltage developed across one of said resistive elements is higher or lower than a prescribed threshold value and causing one of said current supply means corresponding to said one of said resistive elements to control said current depending on the determination,
• wherein said control means comprises:
• first scanning means for sequentially connecting a check point to said resistive elements;
• comparator means for comparing a voltage at said check point with said prescribed threshold value and producing an output signal when the check point voltage is higher than said prescribed threshold value;
• and
• second scanning means synchronized with said first scanning means for sequentially connecting the output signal of said comparator means to said plurality of current supply means to cause said output signal to cease the current supplied to one of said resistive elements to which said check point is being connected.