Circuit boosts voltage to piezoelectric transducers

Piezoelectric transducers are common in ultrasonic and acoustic-alarm-signaling applications. To get enough acoustic power from a piezoelectric transducer, you must power the device with a frequency at or near its resonant frequency. Furthermore, the driving voltage should be as high as the transducer allows.

A transformer circuit drives the transformer and the transducer at resonant frequency. You must usually build and optimize these transformers for the transducer you are using—a time-consuming job. You can, however, drive the piezoelectric transducer without the transformer using the circuit in Figure 1.

The circuit includes an oscillator using Schmitt trigger IC_1A. The frequency depends on resistor R₁ and capacitor C₁. You must select both components to fit the oscillator frequency with the resonant frequency of the piezoelectric transducer. You can replace R₁ with a variable resistor and change the value to maximize the voltage on the transducer.

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The driver includes the five additional inverters of IC₁, IC_1B through IC_1F. A voltage tripler comprises diodes D₁ and D₂ and the surrounding components. The amplifier comprises Q₂, and the piezoelectric driver comprises Q₁ and Q₂.

Diodes D₁ and D₂ come in one BAS40-04 package. Alternatively, you can use double transistors for Q₁, Q₂, and Q₃. You can replace the oscillator with a microcontroller if you have one available. The circuit works with supply voltages of less than 10V. You can use it in 3.3V systems, but you should then use a 74HC14 inverter for the oscillator and the driver. You can also use additional voltage-doubler stages to get even more driving voltage for the transducer.