US Patent 7604321 Thermal inkjet printhead with de-clog firing mode

A printhead IC comprising: an array of nozzles, each with a corresponding heater to form a vapor bubble in printing fluid that causes a drop of the printing fluid to eject through the nozzle; and, drive circuitry for generating drive pulses that energize the heaters, the drive circuitry being configured to operate in two modes, a printing mode in which the drive pulses it generates are printing pulses, and a maintenance mode in which the drive pulses are de-clog pulses; wherein, the de-clog pulse has lower power and a longer duration than the printing pulse.