I found two ways of working with piezo like a buzzer.
In the first case, we use only a resistor. When we turn ON the circuit, I have my transistor off, With Vc=VDC. When the piezo sends a feedback voltage, we have saturation in the transistor; my Vc = 0.2V ( approximated), and the piezo doesn't stretch and feedback voltage = 0V.
But, how does it work using an inductor? When we saturate the transistor, the coil tries to maintain the current throughout the circuit, and a -EMF voltage appears and polarizes my base in reverse and cuts off the transistor. Does this cause an oscillation in my piezo?
Is there any difference in efficiency of each circuit?
Best Answer
The inductor stores energy while the transistor is on, releases it when the transistor is off, giving something like twice the supply voltage (peak-peak) across the piezo.
The resistive version gives a peak-peak voltage that's only equal to the supply.
So the inductive one should be 6dB louder.