Hello friends,

i need to generate a high intensity sound (more than 90dB)by a piezo transducer, we know that piezo's are high impedance,
at now i use from 4069 CMOS IC to drive my piezo's but it is not able to generate enough intensity for me.

does anyone know any way or any circuit to getting that intensity?

thanks alot for any suggestion.

 

Build a switching regulator to generate about 90VDC and using a push-pull driver switch one side of the piezo at its resonant frequency.

 

thanks for your reply,

but any idea about "switching regulator"?

what do you mean by "push-pull driver switch one side of the piezo"?
is your mean putting a resonator?

how can i measure the intensity of my output and the piezo?

 

Operating a piezo beeper at its resonant frequency, with it enclosed in a resonant chamber is the key to loud beeping like in a 9V powered smoke detector. Also, drive the piezo in a bridge of two out-of-phase drivers. Operate Cmos inverters in parallel to get enough current to charge and discharge the high capacitance of the piezo.

A piezo beeper with a built-in oscillator is mounted in a resonant chamber with a size correct for the resonant frequency of the piezo. The piezo has a positive feedback connection that allows the oscillator to operate only at the resonant frequency. You can't do that with a transducer because the resonant peak is very sharp.

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Uncle $crooge

 

Which will totally destroy a normal piezo transducer who's maximum peak voltage is probably no more than 30V, you need an h-bridge driver which can be built using a CMOS 4050 hex inverter.

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Well I have lots of ideas about switching regulators. I usually start with LTSpice's switch selector where I can try different ideas.

A push-pull driver is one that has an active device(BJT or FET) which connects the load to ground and another active device(BJT or FET) that connects the load to a positve voltage. The control for this driver insures that both devices are NOT on at the same time.

As a load the piezo looks like a capacitor. If you are going to charge it up, then you have to discharge it as well. A push-pull driver works well for this. A push-pull driver is sometimes called a half-H bridge driver.

I'm not sure I see the advantage of using a full bridge driver and most piezos will be just fine with 90V provided the current is limited.

You measure the output of the piezo with a sound level meter. I think Bruel & Kjaer make one. Here is a link

http://www.bkhome.com/bk_template1.asp?spid=210&ctid=6

 

Seriously check the datasheet, the highest voltage audio piezo transducer I've found was rated to 60V, 25V or 15V are more typical, 90V will destroy the fragile crystal. I think you're getting confused with the ultrasonic transducers used in cleaning baths which are often rated to >100V.

Attached Files

piezo.pdf (182.2 KB, 39 views)

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I don't think I would actually hear an ultrasonic transducer. I'm quite sure we are beating these things to death in the quest for obnoxious loudness. It is quite loud and it is painfully obnoxious. Don't know about the long term survivability I guess we'll have to see how they hold up.

 

A simpler and safer option might be to use an 8:1k audio transformer with an h-bridge driver, this will make the piexo with an impedance of 1k or so look like an 8 ohm speaker but it'll be a lot louder.

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Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

i have read somewhere that piezo sound pressure level is 6dB larger as
the input voltage is twice larger,
i have seen that piezo data's say mostly that their piezo's can work just fine at 110dB or more, so there should be a way to produce that pressure with a voltage far less than 90V.

i am using from 4069 CMOS as h-bridge and 180 degree phase shift but it can not deliver very high pressures for the piezo.

 

Look on a 'scope of the output ot the 4069 inverter that is driving the piezo. It will be no where near as high as the supply voltage because the high capacitance of the piezo uses a fairly high current.

Then try it with some of the inverters connected in parallel and the p-p voltage will be much higher and the sound level will also be much higher.
You could also use an NPN and PNP pair of emitter-followers to drive the piezo with nearly the entire supply voltage.

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Uncle $crooge

 

i have no sound level meter, can i measure it with my scope? it has a spectrum analyzer.

 

here is the circuit i am using, can you let me know what the problem is realy?

i think i have done what you are saying.

Attached Images

srm1_43.gif (2.2 KB, 42 views)

 

The capacitor in series with the piezo might be reducing the output. The capacitor isn't needed because a piezo is a capacitor.
If the piezo is large then its capacitance is too high for two paralleled inverters to drive without a high voltage loss.

A piezo speaker has very sharp resonances so will be loudest if the frequency is tuned to a peak.

Attached Images

piezo speaker.PNG (52.2 KB, 25 views)

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Uncle $crooge

 

Just an interesting thing... everybody know the small 12VDC piezo syren with 120dB loudness. I'm just curious what kind of driver contain it, and disassemble: it have a simple dual oscillator (syren sound) with BD139! and transformer as driver. The voltage (pp) on the piezo element was 300V!
I think: this is a special piezo, but have tried with a poor quality (made in Hungary) piezo, and work successfull! (first i think, i make a big BANG, because the datasheet say: max pp voltage 20V)
Another thing: Murata and others made piezo buzzers with in-built (one or two transistor) oscillator and a small inductor seriel with power input. (the poor quality piezo-buzzers haven't inductor, and produced less than half sound)