Driving a 600W Piezo transducer for sonar application

Question

I am looking to build a circuit capable of driving a 600W piezoceramic transducer with an impedance of 200Ω at a frequency of 50kHz. Since it is being used in a sonar application only short pulses(around 400uS) will be output around 2-3 times a second.

I am looking to drive it from a 12V source which will need to be stepped up to around 300V. Initially I was thinking on building an amplifier circuit, inputting a sine wave and using the amplifier to drive a transformer.

However I was wondering. Would it be possible to drive step-up transformer with a square wave, simplifying the circuit greatly, and use a band pass filter on the output in order to convert it into a sine to be fed into the transducer?

Any help would be much appreciated. Thanks.

Answer 1

I think you need 346V^2/200ohms=600W

Z at 600W is 200 ohms at series resonance? if valid or V is just rounded down, ok.

then at 12V the impedance ratio is \$(346V/12V)^2=831\$ so the driver sees 300/831=0.36 Ohms

For 1% loss or 6W the transistor ESR (RdsOn or rCE) must be 1% or 3.6 mOhms.

Next what frequency? and waveform? square wave? then you need twice the peak voltage to get peak-peak voltage at 50% duty cycle for 326Vrms if you spec is valid and thus RdsOn.

The transformer DCR primary winding must be similar to RdsOn or less for same losses and you probably need Litz wire for low inductance and use a half bridge driver with +12V on centre tap. as well low ESL wiring from driver is necessary.

I'll add more details as you show more specs. on my assumptions. Do you have a datasheet?

Since this is just peak power, what is the duty cycle and thus average power? 400us/333ms x600W = 0.72W.

You need a well balanced transmission line to prevent pulse ringing and thus false echos from long decay times , which limits your short range.

• so the Q must be low 0.7 like in a good RF amplifier or matched impedance at 50% efficiency . Power loss is not a problem but high Q resonance at a 50kHz frequency with >10 harmonics from a high turns ratio transformer is harder to doand conflicts with shutoff fast response times, than a DC-DC convertor with >50 us response time to loop bandwidth.

  Thus I would step up DCDC supply to say get an equivalent load of 8 Ohms or a turns ratio of 5 and much higher cheaper RdsOn MOSFETs supply low power for lower current driver to get 600W peak.

• then consider a design for class E audio with 50kHz

Thus with a low turns ratio of 5 is a smarter idea to get 1us decay time on the 400 us pulsed 50kHz carrier, lower current driver and easier to manage impedance ratios.

just an idea.

Answer 2

The usual approach (I used to do that stuff for a living) for a narrowband driver is to use a tuned transformer (Wind the secondary to have an inductance that resonates with the transducer fixed capacitance) and go for a sane sort of step up ratio.

This is then typically driven by a third or fourth order matching network, generally with some resistance in the series arm (They tend to go very low Z near the band edges), input power is generally a H bridge. It helps to have a smallish boost (or flyback) taking your 12V up to something more sane and charging a honking great capacitor, a couple of hundred volts at the input to the H bridge stomps all over doing it with 12V.

I did a 1kVA (About 500W of real power @ 10-20KHz) design off a 12V rail, the tuned transformer had a 1.5 turn primary, an air gap measured in mm and a magnetising current of ~100A! It worked well, but my god was it painful, output was hitting 800V RMS.