Hi,

I'm designing an ultrasonic anemometer using 40khz transducers. There are 4 transducers driven single-ended. I'm currently using two L293D's hooked up to a uC to drive each transducer @ 12V/0V. It's working decently, but I'd like to drive the transducers +/- 12V instead of 12V/0V. Or maybe up to +/- 20V.

Can anyone recommend a 3.3v-controlled, dual-supply (+/- 18V) push-pull driver IC? It also needs to have tri-state/shutdown/hi-z mode so that each transducer can become a receiver. I've considered running the L293D from Vcc2=12V, Gnd=-12V and Vcc1=-7V, but then I'd have to bias each of the 8 control inputs, which would be a real pain. I'm currently able to drive the L293D's directly from the uC, which is nice.

Oh, and it would be really nice if they came in DIP

I've looked at a few op-amps, but most of them don't have a shutdown mode (and are a bit on the pricey side). A comparator -might- do the trick, but I haven't been able to find one that can run up to 35Vpp and also disable it's output. And all of the H-bridge drivers I've seen are designed for single-supply control.

Any recommendations or advice would be really appreciated!

 

hi nova,
Welcome to AAC.
Have you considered 40kHz transformer coupling.?

E

 

Hello,

Have you considered the use of two L293 outputs with the transducer between them and an inverter between the two inputs.
That way the transducer will see either +12 Volts or - 12 Volts, doubling the voltage.

Looking at the datasheet of the L293, the supply voltage of it has an absolute maximum of 36 Volts.
When you supply the L293 with 18 Volts and apply the scheme above, you will have your + 18 Volts and - 18 Volts.

Bertus

 

You might consider using an RS232 driver circuit (e.g. MAX3233)which runs on 3.3V and uses an internal charge pump to generate the positive and negative voltages needed for RS232.

 

hi nova,
Have you considered 40kHz transformer coupling.?
E

I have, but I'm modulating the transmission with a barker code and I'm a little worried that when quickly modulating 180 degrees out of phase the inductance of the field windings will muddy up the signal. I have a few 40khz IFT's on order and I'm going to try to mess around with them, but driving the transducers with a nice stiff square wave feels like it would be more accurate.

Hello,
Have you considered the use of two L293 outputs with the transducer between them and an inverter between the two inputs.
That way the transducer will see either +12 Volts or - 12 Volts, doubling the voltage.

Looking at the datasheet of the L293, the supply voltage of it has an absolute maximum of 36 Volts.
When you supply the L293 with 18 Volts and apply the scheme above, you will have your + 18 Volts and - 18 Volts.

Yep I was doing that when I was driving open-structure transducers and it did work well, but the waterproof transducers I'm using now have one of their pins connected to the case of the aluminum transducer. Given that the sensors will be exposed to the elements and end up getting wet, I'm concerned that it'll find it's way to ground and cause interference and/or corrosion (safety concerns aside).

You might consider using an RS232 driver circuit (e.g. MAX3233)which runs on 3.3V and uses an internal charge pump to generate the positive and negative voltages needed for RS232.

The MAX RS232 drivers are indeed awesome and nearly perfect (no need for a negative supply!). I've tried a MAX232 and it worked well, but didn't have a quick or easy way to disable the output. The MAX3223 has an OE pin, but alas, only drives +/- 6V. If only I could find a the exact same kind of chip but able to drive a few more volts. I may still order a few to see how they work out.

 

Hello,

You might want to have a look at some power opamps.
There are types that will work upto 100 volts.

Bertus

 

I have, but I'm modulating the transmission with a barker code and I'm a little worried that when quickly modulating 180 degrees out of phase the inductance of the field windings will muddy up the signal.

hi nova,
You are correct regarding the Phase modulation, both the transformer and transducers will 'ring'' on any Phase change.
Have you carried out any empirical tests on Phase modulation of the transducers, in order to check transducer 'ringing' at the Phase reversal.?

E

 

See

 

Hello,
You might want to have a look at some power opamps.
There are types that will work upto 100 volts.

Thanks Bertus! The LM4700 and LM4765 seem to fit the bill, but are rather power-hungry devices and have a significantly tall profile. Seems like overkill to use a 30W amp to drive transducers that draw a few mW

See
View attachment 144630

Hey now this looks like exactly what I need ... etched into silicon Once these are in full fab production, you can pencil me in for at least 10 of them .. can I get a volume discount?

Really though that's just too many components to use for each channel (x4) - I don't have the board space or the patience to solder them all. Sweet circuit though.

hi nova,
You are correct regarding the Phase modulation, both the transformer and transducers will 'ring'' on any Phase change.
Have you carried out any empirical tests on Phase modulation of the transducers, in order to check transducer 'ringing' at the Phase reversal.?
E

The transducers definitely ring, and the output doesn't really look much like my modulated input, but there are enough full phase reversals for a simple cross-correlation of the channels to remain locked and accurately measure the TOF:

You can see the output from the uC in yellow (two barker-13 sequences sent, with 4 inverting pulses sent per barker-13 sequence code bit). The output of the L293D is in magenta (+12V/0V), and the amplified received signal is in cyan.

I'm somewhat torn - it works "good enough" in my tests, but the receiving amp (two-stage LM358) has a total Q of about 200 and is very susceptible to noise. It would be nice to drive the transducers higher and reduce the amplification. The L293D's also have varying propagation time per-chip which has to be calibrated out. I have no idea if or how much it'll vary with temperature, either. They are very convenient in that each one can drive two transducers and have built in output-disable functionality.

Which raises another question: Is single-ended driving a piezo transducer 12V/0V electrically equivalent to +6V/-6V? Or does the -6V give it more "oomph" when driving the anti-phase part of the signal? Would driving them with dual supplies be as beneficial as I thought it would be?

 

Which raises another question: Is single-ended driving a piezo transducer 12V/0V electrically equivalent to +6V/-6V? Or does the -6V give it more "oomph" when driving the anti-phase part of the signal? Would driving them with dual supplies be as beneficial as I thought it would be?

hi nova,
A bi-polar push pull drive will 'force' the Transducer to change Phase in a shorter time, but you will always have the ring.

On the receiving detector, how is that handling Phase change and ringing.?

E
You may see from my Profile page, I have 'been there , tried that' with my Marine echo sounder products. Transducer ringing is a problem.

 

hi nova,
A bi-polar push pull drive will 'force' the Transducer to change Phase in a shorter time, but you will always have the ring.

On the receiving detector, how is that handling Phase change and ringing.?

E
You may see from my Profile page, I have 'been there , tried that' with my Marine echo sounder products. Transducer ringing is a problem.

There's very little handling to be done - you transmit your signal in one direction, swap the transmitter/receiver and transmit the same signal in the opposite direction. Just cross-correlate the two received signals with each other and the peak is your phase shift = wind speed. The ringing and phase change is identical in both directions (in terms of frequency; the amplitude varies a tiny bit due to transducer differences), and the 180-degree phase change in particular makes the cross-correlation much easier to stay "locked", even across phase shifts greater than one wavelength.

 

hi nova,
That sounds great.
Like to see the final results for bipolar p/p.
Eric

 

Will do! Thanks for the help Eric (and everyone), I really appreciate it.

 

RE:""Can anyone recommend (..) push-pull driver IC""

Rather strong but cheap (under the one dollar) driver may be composed from TC4422/TC4421 (one low side another high side) what are giving the 9 Amp in the gate. I have used that years and years without of any fail.

Another even more powerful choice, if rather one will 30 Amp gate current is needed, be more modern ACPL336G for the same price, with rather sophisticated multilevel safety system genuine built in. However it 2,5 A small output current may be easily corrected by ordinary bjt booster cascade at it output on basis of PHTP60415NY and PHTP60415PY. I am steering the 500 Amp igbt with it and now its about 2 years working with a glance.