> On 11/10/17 20:08, o pere o wrote:
>> On 10/10/17 02:15, 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.
>>>
>>> Thanks - JJS
>>>
>>
>> As John points out in his response
>
> Who?
Sorry, should have been Clifford :)
Pere
Reply by Jan Coombs●October 15, 20172017-10-15
On Thu, 12 Oct 2017 13:48:19 -0700
John Speth <johnspeth@yahoo.com> wrote:
> 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.
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
Reply by John Speth●October 12, 20172017-10-12
On 10/12/2017 6:32 AM, petrus bitbyter wrote:
>
>
> "John Speth" schreef in bericht news:ormah5$4ue$1@gioia.aioe.org...
>
> On 10/11/2017 4:10 PM, Chris wrote:
>> On 10/10/17 00:15, 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.
>>>
>>> Thanks - JJS
>>>
>>
>> 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
>
> |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.
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
Reply by Chris●October 12, 20172017-10-12
On 10/12/17 13:32, petrus bitbyter wrote:
>
>
> "John Speth" schreef in bericht news:ormah5$4ue$1@gioia.aioe.org...
>
> On 10/11/2017 4:10 PM, Chris wrote:
>> On 10/10/17 00:15, 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.
>>>
>>> Thanks - JJS
>>>
>>
>> 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
>
> |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
Reply by petrus bitbyter●October 12, 20172017-10-12
"John Speth" schreef in bericht news:ormah5$4ue$1@gioia.aioe.org...
On 10/11/2017 4:10 PM, Chris wrote:
> On 10/10/17 00:15, 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.
>>
>> Thanks - JJS
>>
>
> 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
|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
Reply by John Speth●October 11, 20172017-10-11
On 10/11/2017 4:10 PM, Chris wrote:
> On 10/10/17 00:15, 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.
>>
>> Thanks - JJS
>>
>
> 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
Reply by Chris●October 11, 20172017-10-11
On 10/10/17 00:15, 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.
>
> Thanks - JJS
>
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
Reply by Clifford Heath●October 11, 20172017-10-11
On 11/10/17 20:08, o pere o wrote:
> On 10/10/17 02:15, 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.
>>
>> Thanks - JJS
>>
>
> As John points out in his response
Who?
Reply by o pere o●October 11, 20172017-10-11
On 10/10/17 02:15, 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.
>
> Thanks - JJS
>
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
Reply by Clifford Heath●October 9, 20172017-10-09
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.