![]() ![]() Q: What about safety? We’re in the higher-voltage regime here, right?Ī: Yes, there are safety issues. This complicates the driver design and topology but is a solvable problem To meet the need for high-performance voltage drive for the piezoelectric element, there are vendors who offer high-voltage op amps in monolithic and hybrid form which can deliver the voltage (and current) needed and can drive the highly capacitive loads.Ī: Of course! The piezo element is “floating” (not ground referenced) so the driver must have a differential output with no reference to system ground. Q: Are those the only driver-design options?Ī: No. ![]() Thus, the drive problem has two parts: providing a DC supply of high-enough voltage, and then developing a high-voltage amplifier which operates from this supply to drive the element. Providing this high-voltage supply can be a challenge, as most basic AC/DC or DC/DC converters produce a much lower-voltage rail at up to several tens of voles. This load may range as high as 1000 nF.Ī: No, regardless of the approach used to build the analog high-voltage driver, the driver itself needs a high-voltage DC rail as its supply. Note that the piezoelectric element looks like a capacitive load (again, in contrast to the inductive load of a motor and its coils) so the voltage driver must be designed for supporting capacitive loads without concern for oscillation or stability issues. Another option is to use a standard lower-voltage op amp but with voltage-boosting transistors (usually bipolar, sometimes FETs) on their output. This works well for small elements such as used in tiny positioning devices (or even piezo-based sounders/buzzers, which are “crude” but effective and widely used). Q: How do you develop such a drive voltage?Ī: At lower voltages, in the tens of volts, standard op amps may be suitable if their process is a higher-voltage one. Fig 1: This piezo-drive waveform is designed to optimize performance for a specific inkjet-printer printhead. ![]() The associated current can be in the range of a few mA to several amps. Of course, there is a current which accompanies a voltage any real time work is done (in the physics sense, as is the case here) but voltage is the controlling parameter. ![]() In contrast, the piezoelectric crystal needs to see an applied voltage, and it is this voltage which determines and drives its action, Figure 1. The ideal motor-drive is a controlled current source, although it can be approximated by a voltage source driving that current. Even though the design engineer may be thinking in terms of applied voltage, it is the current through the coils that the motor “sees” and actually creates the magnetic force, regardless of the drive voltage pushing that current. Q: How does this differ from the drive of a conventional electromagnetic motor, whether AC, DC, brushed DC, or brushless?Ī: All of those motors are current-driver actuators. Q: What are the drive requirements for a piezoelectric element?Ī: It takes an applied voltage, ranging from 30 V to hundreds and even thousands of volts depending on the crystal size, desired elongation, and other factors. Part 2 looks at their drive requirements, which are very different than those of “conventional” motors. Part 1 of this FAQ looked at the moving piezoelectric element of the actuator. Unlike better-known electromagnetic motors, the widely used piezoelectric-based motor/actuator provides precise, repeatable linear motion over short distances, and requires a voltage drive rather than a current drive. ![]()
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