Amplifier vor Piezo Stacks

[Cheeco]

Amplifier for Piezo Stack Actuators

Dear gentlemen,

I am new to this Forum and like to get some advice. I am currently working with piezo stack actuators, "Motors" with small travel and extremely high Forces.

The operating voltage of these motors is from 0-120V. Electrically, they are a capacitive load with 10-40µF. Dedicated amps for these devices are extremly expensive, usually in the range of thousands of Dollars.

I am looking for an alternative, and think that Audio chip amps might be a good solution. I have already seen the devices of Apex, however, I want to try it with Audio amps.

I have a bunch of questions:

• I think that a class A/B amp will be the "safest" way to start. Do you recommend a chipamp with that voltage?
• Negative voltages will break the actuator. Can I supply a chipamp asymetrically? -Vcc = 0V +Vcc = 120V? Do I have to decouple the inputs then?
• Piezo actuators are large capacitances. Do audio amps manage this different load case or will they go nuts? Do I need some adaption circuit?
• Do you think that even a class D chipamp might work for these actuators?

I hope you can help me out here!

Best regards,

Stefan

 

[JonSnell Electronic]

Amacron, (Crown Audio) produced the DC 500 many years ago that was an excellent class B solid state amplifier with a frequency response of DC to 25kHZ. These were used not only for PA use but motor controllers. Class D would be the way to go I think. Not sure there is much to choose from ready made, possibly an IRS2095 driving some tasty FETS on a 120V rail?

 

[jcx]

how fast slew, frequency needed for peak current calc

many chip amps won't like the Cload or the power factor - for narrow band work people often put a inductor in series with the piezo

transformers can be custom wound work to adapt common audio power amps to piezo load but like AC symmetric output

the highest V cheap linear chip amps would be the TDA7293, but the power factor and current requirement would likely want a custom multiply paralleled design, possibly bridged too for high Vswing

a bit of series R in the output stabilizes against the pure C load, needed anyway if paralleling chip amps to share the current

input common mode V limits may make some level shifting or virtual ground arrangement necessary but with DC coupling you can hold the output at any V within the chip amp's spec, offset supply or load "ground"