Have anyone of you had experience using charge to drive a piezo displacement actuator?
I created a piezoelectric actuator driver circuit, using charge, rather than voltage, for displacement. We needed to rapidly move the focal image plane of a microscope with 5000 frame/sec camera, by moving a small mirror mounted on the end of a piezo stick. We wanted say ten Z-axis-stepped images in 2ms.
Our multilayer piezo had a 100V range and had 1.5uF of capacitance. We needed to cover the range in say ten 10V steps. For my first solution, I made a HV amplifier with up to 150mA output, this could do 10V piezo mirror steps in 100 to 200us, using half-to-all of a single frame's image integration time. Ideally we'd do steps quickly, in a small fraction of a frame. So we needed 20x more current, and we needed it fast.
My next scheme was to drive the piezo with charge, rather than voltage. Q = CV = It, and a 2.5A pulse for t = CV/I = 6 us would quickly make a 10V step. My circuit let the user choose step size, number of steps, and maximum piezo voltage. The 2.5A pulses come from a MOSFET plus source resistor, with gate drive from an IR2113 high-voltage HI-and-LO-side IC. The HI side current pulses, I = (Vgate - Vgs) / R. After all the steps, a LO side MOSFET discharged the piezo (so, no charge-leakage drift issues).
Get RIS-741 schematic and info in DropBox folder:
Piezo actuator motion becomes badly non-linear with voltage, especially near the ends of its range. But they show a nice linear displacement vs. charge. For an interesting plot of piezo voltage vs. charge, see the file, RIS-741_meas_01_plots.pdf I observed 20% deviations from linearity over a 120-volt range.