Electronics > Beginners
Need help getting 2.4MHz piezo to oscillate at its resonate frequency
MatCat:
The Piezo is supposed to be roughly 2 ohms at resonate frequency.
T3sl4co1l:
--- Quote from: MatCat on October 28, 2018, 10:08:22 pm ---Another circuit that is often used in actual products is this one, though I don't really fully understand it:
--- End quote ---
And you mentioned elsewhere (in chat) the expected bandwidth is about 4%, i.e., a Q of 25, and this was the datasheet: http://www.dongiltech.co.kr/pdf/DUNU-Series.pdf
Referring to this circuit, it seems to oscillate better (in SPICE) with L1 small (~5n), C1 much larger (~2.2nF), and... C2 controls output power, roughly speaking?
I'm finding better results with the large inductor in the collector circuit, as a usual common-emitter Pierce circuit has it.
I don't like the E-B diode, it supplies excess base current making the V-I dependency hard to control. But it's also necessary to prevent squegging, as given.
You're definitely not going to run it at 50V. 2 ohms and 25W implies 7V RMS. Probably 10-12V supply will do.
These values seem to work nicely:
Tim
MatCat:
--- Quote from: T3sl4co1l on November 08, 2018, 11:13:11 am ---
--- Quote from: MatCat on October 28, 2018, 10:08:22 pm ---Another circuit that is often used in actual products is this one, though I don't really fully understand it:
--- End quote ---
And you mentioned elsewhere (in chat) the expected bandwidth is about 4%, i.e., a Q of 25, and this was the datasheet: http://www.dongiltech.co.kr/pdf/DUNU-Series.pdf
Referring to this circuit, it seems to oscillate better (in SPICE) with L1 small (~5n), C1 much larger (~2.2nF), and... C2 controls output power, roughly speaking?
I'm finding better results with the large inductor in the collector circuit, as a usual common-emitter Pierce circuit has it.
I don't like the E-B diode, it supplies excess base current making the V-I dependency hard to control. But it's also necessary to prevent squegging, as given.
You're definitely not going to run it at 50V. 2 ohms and 25W implies 7V RMS. Probably 10-12V supply will do.
These values seem to work nicely:
Tim
--- End quote ---
Interesting, I will have to try your version of the circuit out. This specific piezo is specified to run at 24V. How much current is that 1 ohm resistor seeing?
T3sl4co1l:
Not much.
That comes to about... uhhh... 0.39A RMS.
These also show reasonable efficiency, consistent with a class C amp/osc. YMMV with a real BU406 or whatever. Probably I'd recommend MJE15012 or another switching or fast-ish amp type if I were designing this. Nudging R and C values back and forth has pretty strong impacts on power output, distortion and efficiency. Probably piezo load has a strong effect as well.
Tim
leeatljs:
The cheap way of driving these 'atomising' piezo's is to drive them from a fairly accurate oscillator. The correct way is to drive them from a waveform which is in phase with the current through the element.
An ultrasonic cleaner works this way, but at a lower frequency than you want.
'greatScott' has a video wich you might find interesing
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