a printhead is provided having fluid ejection nozzles , heaters corresponding to each of the nozzles respectively , with each heater heating printing fluid to cause ejection of a drop of the printing fluid through the corresponding nozzle , and circuitry for generating electrical drive pulses having variable power and length for energizing the heaters . the drive pulses are generated to have less energy than the energy required to heat a volume of the printing fluid equivalent to the drop volume , from the temperature at which the printing fluid enters the printhead to the heterogeneous boiling point of the printing fluid .