AN57; Apex Inkjet Printhead Driver Power Dissipation

AN57; Apex Inkjet Printhead Driver Power Dissipation

Printing industries are rapidly converting from conventional techniques, like offset lithography and rotogravure, to digital technology like inkjet.

The printheads of many industrial inkjet printers use piezoelectrictechnology. In the printheads of so called ‘drop‐on‐demand’ (DoD) inkjet printers the piezoelectric nozzles produce ink drops when driven by electric pulses.

Since the nozzles behave like electric capacitors and the amount of nozzles in a printhead being fired varies continuously, the amplifier driving the printhead ‘sees’ avery dynamic, capacitive load. Apex Microtechnology’s power operational amplifiers are very well suited to drive DoD inkjet printheads as they meet the power requirements of and can be tuned to this specific application by external components.

This application note describes a way to derive the internal power dissipation of an Apex power op amp driving a DoD inkjet printhead.


THE AMPLIFIER AND THE FIRE PULSE


DoD piezoelectric printheads usually contain a large, even number of nozzles, often a power of 2, that can be in a single or in multiple rows. The head also contains digital circuitry through which each  individual nozzle can be set to eject a drop at the next fire pulse or to stay inactive.

The active nozzles are all in parallel when the driver amplifier produces a fire pulse to make them all eject drops simultaneously. Single nozzle capacitance, depending on manufacturer, can vary wildly, but usually is in the range of 150pF to 2nF.

Applicationnotes

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