# [DIY]Transducer driver SMPS

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#### egberttheone

I’m (trying to) building a ultrasonic cleaner for cleaning PCBs.
I have 2 ultrasonic 100W 28khz PZT transducers connected in a parallel fashion.

An externally hosted image should be here but it was not working when we last tested it.

C7,C8,C9,C10,R5,R6,L4,L5 form the equal vent of the transducers.
The resonance frequency of the transducers seems to be f = 28659.9hz.
Therefor the circuit should operate at this frequency.
To compensate for the capacitive of the transducer I have added a inductor L3.
According to the math the impendence of the transducers with the compensation coil would be Z=3.445 ohm.
So the secondary of the transformer (L1,L2) should be 3,445 ohms?
Then the inductance should be 19.13085395µh.

Please ignore the primary halve of the circuit it is not calculated, the values do not make sense.
Can anyone confirm I’m on the right track here?
I’m in a learning phase so please be patient.

Last edited:

#### Elvee

C7,C8,C9,C10,R5,R6,L4,L5 form the equal vent of the transducers.
The resonance frequency of the transducers seems to be f = 28659.9hz.
Therefor the circuit should operate at this frequency.
To compensate for the capacitive of the transducer I have added a inductor L3.
Your pics are utterly unusable, and I don't see what you mean by "vent", but anyway you should operate the transducers at the conditions stated by the manufacturer. At the resonance frequency, the transducer has to be resistive by definition, there should be no need to add something
According to the math the impendence of the transducers with the compensation coil would be Z=3.445 ohm.
So the secondary of the transformer (L1,L2) should be 3,445 ohms?
Then the inductance should be 19.13085395µh.
Certainly not, the transformer needs to have a large enough magnetizing inductance to make it negligible, and probably more importantly, it should have a large enough v*s product to operate at the intended voltage/frequency.

#### egberttheone

Thank you for your kind reply, with "Vent" I actually mend "equivalent".
I'm sorry for the bad quality of the pictures I will re-upload them.

These transducers are always capacitive if it is in resonance, because the equivalent circuit of a transducer shows a capacitor in parallel with the resonance circuit. That’s why an inductor is added to get the phase shift close to 0.

About the transformer: I’m quite new to this array, see picture 2 of the calculated values i have found.

#### Elvee

These transducers are always capacitive if it is in resonance, because the equivalent circuit of a transducer shows a capacitor in parallel with the resonance circuit. That’s why an inductor is added to get the phase shift close to 0.
The effect of the parallel capacitance will normally be tiny, and will be compensated by a small shift in the resonance frequency, you don't need to add explicit compensation components.
If you want to drive them at a different frequency, then it could be important.

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