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Re: Can a piezo buzzer generate damaging voltages?

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On 10/10/17 11:15, John Speth wrote:
> My team is being asked to find out why a circuit is failing for no 
> obvious reason.  The circuit has a piezo buzzer (CEP2242 from CUI, Inc). 
>   The buzzer is driven by a MCU driven FET that completes a circuit like 
> this: high side power 3.3V -> buzzer -> FET -> ground (BSS123LT1 FET on 
> the low side).
> 
> Does anybody have any experience with the possibility of a piezo buzzer 
> generating damaging voltage spikes when dropped?  We have no protection 
> diodes on this part of the circuit.
> 
> At this stage, we have no information of exactly what's failing.  We do 
> have evidence that some failed units have been dropped.  I'm following 
> through on a hypothetical failure path which we need to either consider 
> further or discard.

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.

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Thread

Can a piezo buzzer generate damaging voltages? John Speth <johnspeth@yahoo.com> - 2017-10-09 17:15 -0700
  Re: Can a piezo buzzer generate damaging voltages? Clifford Heath <no.spam@please.net> - 2017-10-10 13:55 +1100
  Re: Can a piezo buzzer generate damaging voltages? o pere o <me@somewhere.net> - 2017-10-11 11:08 +0200
    Re: Can a piezo buzzer generate damaging voltages? Clifford Heath <no.spam@please.net> - 2017-10-11 22:37 +1100
      Re: Can a piezo buzzer generate damaging voltages? o pere o <me@somewhere.net> - 2017-10-16 09:56 +0200
  Re: Can a piezo buzzer generate damaging voltages? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2017-10-11 23:10 +0000
    Re: Can a piezo buzzer generate damaging voltages? John Speth <johnspeth@yahoo.com> - 2017-10-11 16:46 -0700
      Re: Can a piezo buzzer generate damaging voltages? "petrus bitbyter" <petrus.bitbyter@hotmail.com> - 2017-10-12 15:32 +0200
        Re: Can a piezo buzzer generate damaging voltages? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2017-10-12 14:31 +0000
        Re: Can a piezo buzzer generate damaging voltages? John Speth <johnspeth@yahoo.com> - 2017-10-12 13:48 -0700
          Re: Can a piezo buzzer generate damaging voltages? Jan Coombs <jenfhaomndgfwutc@murmic.plus.com> - 2017-10-15 18:12 +0100

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