Help Amplifying Transducer with LM324 OP Amp

Thread Starter

Ben Slayton

Joined Apr 24, 2017
5
Hi, I need help amplifying the sound/output of this transducer. I have verified that the input of the op amp is 25 KHz and the output is as well. I just cannot get the transducer enough power.

Details:
Thanks for any help or insight anyone can offer.

PS. I am pretty new to circuitry. My background is in Software Development. Please bear with me if I use the wrong terminology. Trying my best to learn. :)

Edit: I spoke with someone at American piezo and he said that I need to push 30 VRMS to the transducer. So I would like to do that, or at least go as high as the op amp supports.
 

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dl324

Joined Mar 30, 2015
17,110
Welcome to AAC!

Thank you for posting a schematic. What is the amplitude of the input signal, how is it coupled?

Some members have slow or very slow connections. Please post images with an appropriate resolution.

Clipped output waveform info:
upload_2017-4-29_14-7-32.png

And uninteresting Arduino output:
upload_2017-4-29_14-10-3.png

Breadboard - note, 9V supply, not +/-9V as indicated in schematic:
upload_2017-4-29_14-19-14.png
 
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Thread Starter

Ben Slayton

Joined Apr 24, 2017
5
Some members have slow or very slow connections. Please post images with an appropriate resolution.
Good point. I'll make sure to lower the resolution.

Breadboard - note, 9V supply, not +/-9V as indicated in schematic
Ahh, I didn't catch that. How can I get -9v?

I stand corrected ... but if you want to increase the magnitude of the input/output voltage, the supply voltage will have to be increased.
I replaced the 9V battery with a 30v supply, which accomplishes what I needed... a louder transducer.

Now my issue is that the square wave is distorted at the op amp output.

OP-Amp Output.png
 

drc_567

Joined Dec 29, 2008
1,156
To get a better square wave output, try placing power supply bypass capacitors near the connections. This might consist of a 10 uF electrolytic, and a 0.1 uF ceramic, non-polar capacitor, immediately adjacent to each power supply connection.
 

jjw

Joined Dec 24, 2013
823
LM
Good point. I'll make sure to lower the resolution.



Ahh, I didn't catch that. How can I get -9v?



I replaced the 9V battery with a 30v supply, which accomplishes what I needed... a louder transducer.

Now my issue is that the square wave is distorted at the op amp output.

View attachment 125782
You need faster opamp.
LM324 can output at 25kHz only about 5V peak to peak undistorted sine wave.
 

bertus

Joined Apr 5, 2008
22,304
Hello,

The slew rate comes into play with large signal output.
The edges will become slopes due to the speed of the opamp:

LM324_pulse_responce.png

Also with higher frequencies the output may not get to the full range of the opamp:

LM324_large signal responce.png

Bertus
 

drc_567

Joined Dec 29, 2008
1,156
The sharp corners of square waves consist of higher frequency sine waves. If those sine waves are attenuated ... not amplified 100%, then the output waveform shape will be distorted.
So, it may be that you need a different op amp, one that can deal with the higher frequency components.
 

Thread Starter

Ben Slayton

Joined Apr 24, 2017
5
LM

You need faster opamp.
LM324 can output at 25kHz only about 5V peak to peak undistorted sine wave.
Also with higher frequencies the output may not get to the full range of the opamp:
The sharp corners of square waves consist of higher frequency sine waves. If those sine waves are attenuated ... not amplified 100%, then the output waveform shape will be distorted.
So, it may be that you need a different op amp, one that can deal with the higher frequency components.
Thanks. That makes sense. Any suggestions on what I can replace this with? I found this chip, but cannot find a through hole version - http://www.ti.com/product/LM48580
 

drc_567

Joined Dec 29, 2008
1,156
The TI component looks like a possibility.
Sometimes, there are adapters that allow the utilization of surface mount and similar devices in macro applications.
So, suggest that you contact TI directly and inquire what implementation is available.
 

MrChips

Joined Oct 2, 2009
31,072
If you want to drive a piezoelectric transducer with 25kHz 30V square wave, you don't need an opamp or split power supply. All you need is a single 30V supply and a driver transistor.
 

drc_567

Joined Dec 29, 2008
1,156
OP seems to be concerned with portability ... The TI LM48580 contains a built in voltage booster ... 30v and 800 mw power from a 3.6v battery.

The only issue is obtaining a ball grid array adapter socket to allow construction.

This place has socket adapters ...
info@ironwoodelectronics.com
 
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Thread Starter

Ben Slayton

Joined Apr 24, 2017
5
The TI LM48580 contains a built in voltage booster ... 30v and 800 mw power from a 3.6v battery.
Seeing that I switched to a step up converter to use with 3.7v lipo, I could ditch the step up converter with this chip? I'm I correct in my understanding that it has a step-up converter built in? That would reduce space by a good margin.

If you want to drive a piezoelectric transducer with 25kHz 30V square wave, you don't need an opamp or split power supply. All you need is a single 30V supply and a driver transistor.
I just tried this with ~20 volts and my square wave is still distorted, though not as bad, and not loud at all, unlike when I was using the op amp. I based my circuit on this, with a TIP122 transistor:


probe-connected-to-collector.jpg
 

drc_567

Joined Dec 29, 2008
1,156
Are you filtering the power supply connections ... an electrolytic and a non-polar cap at each power supply?

... Something to try ... decrease the base resistor on the transistor to maybe 500 ohms. This will turn on more current and increase power output ... Check temp of the transistor ... not too warm.

The LM48650 would have a built in voltage boost. ... Just have to try it out. ... In earlier times ... TI would send a free sample on request ... not too sure about now. ... Also require socket adapter for 12 pin ball grid array.
 
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