From: Winfield Hill
Subject: Re: Need real loud anti-dog barking ultrasonic device.
Date: 12 Dec 2002 07:23:23 -0800
Organization: Rowland Institute
References: <email@example.com> <3DF73938.2C99A7B4@cern.ch> <3DF88597.60AD3446@cern.ch>
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>Winfield Hill wrote:
>> Very nice. I like the feature allowing a lower-voltage battery.
>> That reminds me, one ought to be able to use a dual MOSFET driver
>> IC to more easily make such a monster beeper,
>. ___________|| ||______________________________
>. | ||___|| |
>. | #
>. | Vbatt (5 to 9V) L #
>. | ,--|<|--+-----o #
>. | | | |
>. | +---|(-- gnd |
>. | | | | |
>. | | R R TC4426 |
>. D /| | | |\ D
>. G--+-O< |--+ +--| >O-+--G
>. S | \| | | |/ | S
>. | | | \ / | |
>. gnd | gnd \/ | gnd
>. | C /\ C |
>. '-/\/-||-' '-||-/\/-'
> Indeed, that trims things down quite a bit. I clearly
> missed a few obvious simplifications. Yet, allow me to
> point out that the 560uH inductor in series with the
> tweeter makes a huge difference, as it reduces its
> -very reactive- impedance to something almost entirely
> resistive. Someone on this forum recently stated that
> impedance matching is an RF issue, without relevance
> at audio freqencies. This, then, is an exception.
Right, sorry for the omission. An inductor to resonate
with piezo's capacitance can greatly increase the drive
voltage on the piezo, even by 10x or more, but only if
the inductance value is chosen for resonance.
I've added back to the sketch above a diode I had left
out from your drawing, thinking it unnecessary. But on
reflection, the transformer's leakage inductance could
make this a necessary part for smooth startup.