How to drive piezo atomizer?

I am in need of some help as I attempt to improve my circuit design
skills. I am trying to reverse engineer one of those aroma dispensers
that use the little piezo-electric atomizers and a bottle of smelly
oil. I have measured and characterized the signal at all the nodes on
that circuit.

The trouble is they put that lame potted bare silicon die on the board
so you have no idea what it's doing. I want to put on a little
microcontroller or something and drive the atomizer for myself. The
signal going into the power mosfet part is essentially a 3V square
wave with maybe a 35% duty cycle. It comes out of the mosfet into a
little transformer (which I am not understanding it's connections, but
that may be another discussion), a big 3300uF cap and a 220uH inductor
before going out to the atomizer.

There is a cap, a diode and another inductor but they all seem to be
on the input side of the silicon part - possibly just for timing and
blocking?

Anyway, if any of you kind and smart folks out there (does sucking up
work in this group?) have any pointers for me I would very much
appreciate it. It seems fairly simple, but I'm not able to completely
recreate the final output signal. I have a function generator but I
can't figure out how, or if it's possible, to set the duty cycle to
something other than 50%. When I drive my circuit with the closest
signal I can get, it doesn't get anywhere near the 150V (220v pk to
pk) needed for the atomizer.

Many thanks in advance.

 

The output impedance of your function generator might be limiting the
rate of rise and fall on the signal at the MOSFET gate. Also, and
more likely, the duty cycle is probably a very important part of the
resonant circuit. Try using the generator output to drive the trigger
input of an LMC555 (capable of operating at 3V) configured as a
monostable (one shot). Use a potentiometer in series with a fixed
resistor to allow you to tweak your duty cycle to duplicate the black
box signal.

http://www.national.com/mpf/LM/LMC555.html

Reverse engineering is, after all, engineering. You need to get
crafty. You know what's coming out of the black box. Follow Mr.
Fields' advice and muscle out the rest of the circuit. Get it down on
paper. It helps.

By the way, if you post back, you might want to mention which function
generator you're using (and whether you have a scope). Newsgroups
can't read minds.

And Google is your friend. Try "piezoelectric atomizer" (no quotes)
and explore.

Cheers
Chris

 

What frequency is your generator set at?
The ceramics are usually pretty high Q, so you need to be close on
frequency.
I don't think you need anything other than a 50% duty cycle.
Mike

 

these are just scaled down from piezo humidifier designs. get a few of
those schematics and like the other guys have said, as long as the ceramic
is driven at the right freq (usually major mode, but often using harmonics)
you can vibrate any liquid into scattered partiticles to drift off away
into the air. i have used those cheapy peizo buzzers to perform this task
with a little mod. most already have the circuits built into the case (and
they are cheap)

us navy has done extensive research on ceramic transducers, they may have
some design unique designs for incidental information also.