3V lithium I/P, 9-12V O/P unreg is ok. 5mA min, 10 mA max, but must have on/off control. Turn on time of up to 5mSec. is ok. Problem is to drive a 12V self oscillating piezo from a 3.3V micro.... TIA
Do you have a pwm output available, or can you afford to make a software pwm waveform? Figure 10-25% duty cycle at 20-500 KHz. Then a very simple inductive boost circuit will work.
Yes I can get a pwm output,but even a simple inductive boost cct is beyond my knowledge. The larkin cct is ok but there's lots of components and I need to turn it on and off. Easy with software pwm O/P... Easy with a boost chip as well but I can only find expensive ones....
Yes, even with 3GHz quad xenon server with 8G memory. Every time I post, people are hitting the server all at once. Try a little later, it should be better.
+3.3 | | L | diode | +-------ak-----+------out | | d | pwm----------g fet cap s | | | | gnd gnd
Fet is a small logic-level n-channel mosfet.
L could be, say, a small 200-500 uH inductor.
Diode is almost anything, 1N914, whatever.
Cap is, say, 0.1 uF
Just futz with the pwm duty cycle and period until the output voltage is right. Try maybe 25% on, 100 KHz to start.
The output can't go below 3, so it's possible the piezo may peep a little down there. If so, you can use another fet or just a port pin to open its low side.
Or you could do this, which does go to zero when you quit driving it...
+3.3 | | L | diodes | +----cap-----+----ak-----+------out | | | d | | pwm----------g fet k cap s a | | | | | | gnd gnd gnd
or this, with a small transformer,
+3.3 | | +--------ak------+-------out | | | x||x* | x||x c x||x | *| | | | gnd gnd | | | d pwm----------g fet s | | gnd
An RS232 level translator such as a MAX3232 (or equivalent from another vendor) can be an easy solution to this. It has a charge pump step up converter built in (just needs a few small caps) and you can either use the enable signal where available or put a diode in series with the output to drive a self-oscillating sounder by controlling the input. You could even drive a piezo sounder (non-self oscillating) directly and give it 40v p-p.
The MAX3232 is guaranteed to provide 10V between the outputs when driving 5mA total. (2.5mA each).
Thanks for all the answers and help. I have enough to get a solution I think. Not going to 0 is ok as the piezo is cpu controlled and puts out a hi(3V3) for off and the pwm will be off. neat idea on the 40Vp-p with a max chip too!!
One last thought: Zetex (and others) make tiny LED driver ICs that are meant to do exactly what you want. They come in regulated and unregulated versions and make up a boost supply as others have mentioned. ZXSC310 is just one example.
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