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Adding 20 volt bias for a 2 amp load

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larry_gorham

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I’m trying to use a 100 watt mid frequency amplifier (PAX100) to drive a piezoelectric load at 600 kHz (PA2JEW); however it requires an all positive drive voltage. The output is +/- 20 volts but I need 0-40 volts at ~2 amps. I’ve tried several techniques found here and elsewhere but they all require lots of power losses or just use low power op amps. Thanks. Larry
 

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As the piezo has high DC resistance, a simple bias-T should do the trick.
 

FvM

No actually I tried that. I have to drive at anti-resonance where the resistance is near zero. Also ThorLabs recommended 50 ohms to limit current to 1/2 amp per chip. I want to drive 4 chips in parallel.

I built a rudimentary amplifier (attached) for preliminary testing but I'm more of an analyst type EE so it only produces 1 or 2 watts. It did confirm the resonance short.

Thanks
Larry
MosfetAmp.jpg
 

Astable H-bridge, 4 transistors cross-biased. Oscillations arise from one capacitor in a strategic spot.

My simulation has a resistive load which gets bipolar 30 VAC 2A 600kHz. However with some effort you may find a way to obtain a frequency based on your piezoelectric load or resonance or anti-resonance.


astable H-bridge cross-biased 4 transis 600 kHz load gets 30v 2A.png
 
Do you need continuous adjustment of the output
crest voltage all the way from 0 to 40V? That's tricky.
Most amps and drivers require some minimum
supply voltage. And somewhere at the low end
you may find self-oscillation hard to sustain.

Do you need a true sine wave or can the piezo
just "suck it up" (ignore the harmonics away from
resonance? This would allow many options from
the power conversion field (subject to the need
for zero-to-max operation).

Can you use an external 600kHz signal to drive
the piezo with adequate results, instead of trying
to self-oscillate?
 
Last edited:

Yes, Dick_Freebird I am driving the above rudimentary amp using a Koolertron signal generator with a pure sine wave at 623 kHz. Powering the resistor only produces 2-12 volts or about 1 watt. With the piezo in series it works fine rejecting unwanted harmonics. But I need more power, 12 watts for one and 50 watts for 4 piezos. Can you suggest a design?

BadtheRad suggested an H bridge (thank you) that generates the power. I can't tell if it will deliver the full peak to peak voltage (0-40) required by the piezo and I need to drive it with my signal generator.

Regardless, thanks for the help - Larry
 

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