High-Voltage Piezoelectric Drivers for Inkjet Print Heads

As shown in the diagrams below, the ink chamber is surrounded by a piezoelectric material, which injects and ejects ink when expanded or contracted. High-voltage (HV) drivers are needed to generate a series of high-voltage pulses, activating the piezoelectric medium to drive the ink in and out of the chamber. The piezoelectric element expands and shrinks based on the voltage polarity across the material. The ink volume can be precisely controlled based on the voltage applied; precise high-voltage drivers allow for precise ink control.

• Apply high voltage (from 50 to 200V) across a piezoelectric element to create mechanical movement
• Modulate the actuation pulse duration, voltage level and polarity to control drop mass and speed
• Slew rate requirement for different print head design varies from 40 to 120 V/ms
• What can you control?
• Slew rate: Controls the ink droplet velocity
• Pulse amplitude: Controls the ink droplet mass
• Pulse width: Controls the repetition rate

• High current capability
• High slew rate
• Low on-resistance
• Low drift
• Low-temperature coefficient
• Tradeoff between voltage, current, slew rate, power consumption, and channel density

Applications:

• Paper printing
• Textile printing
• Ceramic tile printing
• OLED panel printing
• 3D printing
• Biomedical printing

Piezoelectric Driver Circuit Topologies:

• Open-drain output
• Up to 300V
• Unipolar push-pull output
• Up to 300V
• Bipolar push-pull output
• Up to 200V
• Operational amplifier
• Up to 300V up to 1000 V/ms

Ink droplets are generated continuously and accelerated toward a printing target. On their way, these ink droplets pass by high-voltage electrodes controlled by fast switching HV drivers. During this process some droplets are electrostatically charged, while others are not. Next, they pass by a high-voltage deflection plate. The uncharged droplets are allowed to reach the target, while the charged ones are deflected into an ink gutter for recycling.

High-voltage pulses applied to a piezo ink chamber alter the state of the chamber in order to interchangeably suck in, form and push out a droplet of ink and then propel it in direction of target (paper, fabric, etc.). To match the resonance characteristics of the ink chamber, the HV driver generates a series of high-voltage pulses of a particular height, duration and shape.

The piezoelectric element behaves like a capacitive load

• The capacitance varies from a few tens of picofarad to a few nano-farads
• Series resistance varies from a few tens of ohms to a few hundreds of ohms
• Slew rate: dVc/dt = I/C

The HV513 is a low-voltage serial to high-voltage parallel converter with eight high-voltage push-pull outputs. It can be used to drive small capacitive loads such as piezoelectric transducers. It can also be used in any application requiring multiple high-voltage outputs with medium-current source-and-sink capabilities

The HV583 is a unipolar, 128-channel low-voltage serial to high-voltage parallel converter with push-pull outputs. It can be used in applications requiring multiple high-voltage outputs with current sinking and sourcing capabilities, such as plasma displays and inkjet printers.

The HV5523 is a low-voltage serial to high-voltage parallel converter with open drain outputs. It can be used in any application requiring multiple-output, high-voltage current sinking capabilities, such as driving inkjet and electrostatic print heads, plasma panels and vacuum fluorescent or large-matrix LCD displays.

The HV5623 is a low-voltage, serial-to-high-voltage parallel converter with open-drain outputs. It can be used in any application requiring multiple-output high-voltage current sinking capabilities, such as driving inkjet and electrostatic print heads, plasma panels and vacuum fluorescent or large-matrix LCD displays.

The HV7620 is a low-voltage, serial-to-high-voltage parallel converter with push-pull outputs. It can be used as a driver for color AC plasma displays. The device has four parallel 8-bit shift registers permitting data rates four times greater than the speed of one.