Adding bias to a high power load

Thread Starter

larry_gorham

Joined Oct 6, 2019
3
I’m trying to use a 100 watt mid frequency amplifier to drive a piezoelectric load at 600 kHz; however they require an all positive drive voltage. The output is +/- 35 volts but I need 0-70 volts at ~2 amps. I’ve tried several techniques found here and elsewhere but they all require lots of power losses or use low power op amps. The amplifier has a standard 50 ohm output which I am impedance matching with hand made transformers. Thanks. Larry
 

ericgibbs

Joined Jan 29, 2010
12,901
hi larry,
Welcome to AAC.
What is the configuration of the 100W amp output stage.?
Do you have datasheet for the 600kHz piezo.?
E
 

Thread Starter

larry_gorham

Joined Oct 6, 2019
3
Hey, thanks for responding. I built a Mosfet amp that provides the positive waveform but I'm not that good with design. I only get 1 or 2 watts. As a preamp it will drive the PAX100 amp (LTspice attached) with added capacitor-inductor output and impedance matching transformer, no shown .

MosfetAmp.jpg
The PA2JEW's piezo chip can only take 1/2 amp so a 50 ohm limiter is required since they are near zero ohms at resonance. For now it would be great if you could help me drive just one chip to maximum (0-70 volts, 0.5 amps). A better design for the Mosfet amp would probably work since I only need 12 watts for one chip.

Later I want to run 4 chips in parallel, hence the 2 amp max. load. The PAX100 amps are very fussy about driving a 50 ohm load so I'll need another impedance matching transformer to drive multiple chips prior to adding the bias.

Thanks again for your help. This website provides a great service for us amateurs - Larry
 

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Thread Starter

larry_gorham

Joined Oct 6, 2019
3
I made a mistake accepting the 0-70 volts range limit in the piezo spec. ThorLabs suggested 50 ohms would be acceptable but that would exceed the 0.5 amp maximum. I’m keeping the 50 ohm load because of impedance matching so that means I can’t exceed 0-41 volts.

Also my rudimentary amp may be able to do 12 watts if I increase the MOSFET voltage to 70 volts and leave the opamp at 30 volts; that is only according to LTspice.

I still need a way to interface the PAX100 to go beyond one piezo chip.

Thanks - Larry
 
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