DC Driver for an Ultrasonic Piezo Mist Generator.

This is my first post on this forum and after some searching I am still in need of some help. I am trying to build a driver for this: https://www.steminc.com/piezo/Piezo_PDF/BR_SMUTD25F1660R_SA.pdf which is an ultrasonic piezo ceramic transducer for generating mist. I was donated two of these and two of the resin coated piezos to use as part of a fuel cell system for an alkaline fuel cell. So I have DC available and have been in contact with the company who supplied me with the piezos about how to drive them. They sent me a diagram very similar to this diagram: **broken link removed**

I can probably build this but I have my doubts about supplying it with DC voltage as the diagram shows AC input.

What I'd like to do ideally is to drive the piezos with a PWM driver, the drawback to that is the company that donated the piezos said that the PWM would have to provide the correct frequency (1.6 Mhz I think), voltage and current.

Does anyone have any direction on where to start looking for an appropriate PWM driver, or can someone suggest a diagram that I could use?

Thanks for the help in advance,

Nate

Power is input through a bridge rectifier, so you can just as easily use DC as AC.

madeintaiwan said:

What I'd like to do ideally is to drive the piezos with a PWM driver, the drawback to that is the company that donated the piezos said that the PWM would have to provide the correct frequency (1.6 Mhz I think), voltage and current.

Click to expand...

Why do you want to modulate the signal to the piezo with PWM? Are you trying to vary the power to the pizeo? If so you would have to use a frequency much higher than 1.6MHz (probably at least 10 times) and then PMW modulate it with a 1.6MHz signal, a rather difficult task.

crutschow said:

Are you trying to vary the power to the pizeo?

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Not necessarily, I was thinking that if I wanted to generate more or less mist I could vary it with PWM, but I think initially one set amount will work as long as I can regulate the amount for testing purposes.

madeintaiwan said:

Not necessarily, I was thinking that if I wanted to generate more or less mist I could vary it with PWM, but I think initially one set amount will work as long as I can regulate the amount for testing purposes.

Click to expand...

You can probably do that by varying the voltage. A simple way would be to use a variac from the AC line to the input of the 24V transformer supplying the circuit..

crutschow said:

A simple way would be to use a variac from the AC line to the input of the 24V transformer supplying the circuit..

Click to expand...

Thing is, my power supply is an alkaline fuel cell, which is DC and can be any voltage that is needed (as our demonstration stack is ~1 Kw) to run the system components. So my input supply can be a direct 24v DC and I wanting to find out how to drive piezo, as you said the PWM option may be difficult because it has to be variable frequency between 1.6 Mhz and 16 Mhz. Is there perhaps another way to drive a high frequency piezo like that with 24v DC?

You say the fuel cell can be any voltage that is needed. Is that true or do you mean any current? Certainly if you can vary the 24Vdc voltage to the circuit, that should vary the output of the piezo.

Another way to vary the voltage is to use a regulator such as an LM317. You can configure it with a pot adjustment to go from maximum to 1.2V minimum. It will operate with up to 37V input.

crutschow said:

You say the fuel cell can be any voltage that is needed.

Click to expand...

The fuel cell voltage varies due to load, the wattage is constant, I have already set up a LM317 with a pot to control the blower motor that supplies air to the fuel cell. I can do the same with the piezo, although I think that it needs to be switched on and off?

crutschow said:

Is that true or do you mean any current? Certainly if you can vary the 24Vdc voltage to the circuit, that should vary the output of the piezo.

Click to expand...

Thats is the reason I was thinking about using PWM to produce an ultrasonic frequency...

power control alternative

I understand your objective is be able to control amount of mist generated

alternative to vary voltage or try to do pulse width modulation at hi freq. is:

a simple approach is similar to pulse width modulation but control on_time and off_time of power input.. to the driver unit

the idea is .. two timer

first one fixed 60 second (that is fix period)
second one variable ranging 1 second>> 59 second
adjust the timer = adjust amount of mist

1) if you choose 1 second On_Time amount of mist shall be 1/60 1.6 %
2) if you choose 59 second amount of generated mist is 59/60 98 %

Operation Detail where second timer set at 1 second

Power on the system ..

both timer start
full power to the driver duration 1 second (On_Cycle control by second timer )
follow by Off_Cycle until the first timer reach 60 second period then repeat

.. both timer start
full power to the driver duration 1 second On_Cycle control by second timer
follow by Off_Cycle at the end of first timer 60 second period repeat

the figure 60 second period is for explanation purpose only
could be 2 second for a fast response time

two timer should be replace with a simple ic circuit plus solid state relay
it is simple and reliable. you can expect 2 % timing accuracy and cheap

you can use 2 digital timer and solid state relay for pilot unit test. It save time then you can start collect data right away

you can reverse operation on_time is a fix timer and off_time is a variable timer
but the relationship between variable off time and amount of mist is non linear

bye
komgart

crutschow said:

You say the fuel cell can be any voltage that is needed. Is that true or do you mean any current? Certainly if you can vary the 24Vdc voltage to the circuit, that should vary the output of the piezo.

Another way to vary the voltage is to use a regulator such as an LM317. You can configure it with a pot adjustment to go from maximum to 1.2V minimum. It will operate with up to 37V input.

Click to expand...

Hi
Crutschow. Will you plz explain me how the Ultrasonic humidifier works? At what frequencies the mist produces and what are the various sizes of the mist particles at various frequencies.
Cheers

Hello friends,
I just want to make the same mist generator work, but the diagram here seems to be gone. I will be using Arduino UNO as the controller of the things in project, and some DC adapter as power supply. What would be the simplest circuit to run like 3-4 of these mist thingies?