Can a piezo buzzer generate damaging voltages?

I think that's entirely possible.

I used "birthday card" piezo wafers glued to the back of a piece of 1/8" plywood, and using a high impedance 100MHz oscilloscope, measured up to

1kV just from tapping a screwdriver handle on the back of the plywood, pulses around 3ms cycle time (probably from the resonant frequency of the plywood). Without the plywood, voltage could be much higher.

I played with various load impedances, both resistive and capacitive, and my summary of the behaviour is that a given impact dislodges a given number of electrons, and produces whatever voltage is needed to move them. If you have no load, just your output driver, you need to deal with however many uJ of energy a bump will produce, without the voltage causing damage.

In short: if you're seeing damage, use a TVS or back-to-back zeners, or use a small load impedance (1K or less).

Clifford Heath.

As John points out in his response, the answer is yes. A piezo igniter works on this principle. It is a bidirectional transducer from mechanical to electrical energy.

You can test it placing a scope on the terminals of the buzzer and see what comes out.

Pere

Who?

Piezo buzzers are capacitive, so do you have a load resistor across the piezo ?, otherwise no current will flow other than for the first pulse, which charges up the capacitance. A load resistor might fix the spike problem, though clamp diodes to ground and to the +3.3 volt rail, to limit excursions, would be a better solution...

Regards,

Chris

Thanks, Chris. You raised a good point I hadn't considered (capacitance). I suppose the buzzer has a built-in load resistor because the circuit doesn't have a discrete load. The data sheet doesn't say one way or the other. I'll need to look into that.

JJS

|capacitance). I suppose the buzzer has a built-in load resistor |because the circuit doesn't have a discrete load. The data sheet |doesn't say one way or the other. I'll need to look into that. | |JJS

According to the datasheet this buzzer is DC powered and it has a driving circuit build in. The voltage range is 3-16 V and it will draw 7mA max. Next to impossible to damage other components unless it is defective itself or used in a very wrong circuit design.

petrus bitbyter

Ok, so you first need to determine which parts are failing, though a high voltage spike could be getting past the driving circuit, or be a complete red herring. Not enough data...

Regards,

Chris

Yep, you've exposed my ignorance :) I totally missed that datasheet info. While it doesn't eliminate the possibility of buzzer induced damage, I think it greatly reduces the possibility.

JJS

If the buzzer has an internal L-C filter on the power line then you might still have interesting spikes from sending audio square waves to it...

Jan Coombs

Sorry, should have been Clifford :)

Pere