Kurt Nell, Austria
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.
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Figure 1. |
Five inverters and a voltage tripler drive a piezoelectric transducer. |
The circuit includes an oscillator using Schmitt trigger IC1A. 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.
The driver includes the five additional inverters of IC1, IC1B through IC1F. A voltage tripler comprises diodes D1 and D2 and the surrounding components. The amplifier comprises Q2, and the piezoelectric driver comprises Q1 and Q3.
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.
