Piezo Buzzer Diode Snubber

Summary

This short post illustrates, using oscilloscope captures, why a requirement exists to include a snubber, such as diode, across a driven (externally modulated) Piezo buzzer element. 

Unsuppressed Circuit
In the schematic below using a Kingstate Piezo buzzer, the snubber component usually in parallel with the Piezo buzzer was omitted.

Unsuppressed Piezo Buzzer

The capture shown in the image below was measured across MOSFET (S1) whilst being driven at a supply rail voltage of 5VDC. Voltages were measured in excess of the supply rails due to the nature of the piezoelectric element.

Component S1 Drain Voltage Unsuppressed

Suppressed Circuit - Diode
Piezo manufacturers usually state that a resistor, diode, Transorb or similar device should be placed in parallel with the buzzer to manage any energy created by the piezoelectric effect.

Component S1 Drain Voltage Suppressed

The capture above shows the reduction in peak voltage, close to the supply rails, when a general purpose diode was fitted across the Piezo buzzer. Results using a 5.1V Zener diode are identical to a general purpose diode.

Diode Suppressed Piezo Buzzer

The circuit shown above implements a diode for snubbing. For a measured peak voltage of almost 30V without suppression, a diode with a reverse breakdown voltage of double the recorded value was chosen.

Suppressed Circuit - Resistor
In some Piezo manufacturer datasheets, suppression is achieved with the use of a resistor. A resistor may be a cheaper solution to snubbing although the value of the resistor should be selected carefully.

Shown below is a capture, performed in the same manner as the previous section, using a 1K resistor in parallel with the Piezo buzzer. The resistor value was selected because it appeared to be a common value shown on posts and forums. Unfortunately the resistance is far too high and voltages in excess of the supply rails are still developed in the circuit.

Resistor 1K Suppressed Piezo Buzzer

Reducing the value of the resistor by a factor of ten yields improved suppression as seen in the capture below. The reduction in peak voltage is almost fifty percent.

Resistor 100R Suppressed Piezo Buzzer

Summary
For any device requiring electronic suppression, being prudent with the type of suppression can provide considerable differences in the result. The captures in this post were applicable to an externally modulated Piezoelectric element with suppression fitted in parallel with the Piezo.