I managed to destroy a couple of self-oscillating piezo buzzers recently by blocking the sound hole with a blob of Blu-Tack (the beeping was getting very annoying while I was testing a circuit), which is an entirely new way of breaking something to me. These are the buzzers that run off a DC voltage and don't need any drive circuit, as they have an internal Hartley oscillator like so:
[Diagram from Murata]
I guess me blocking the sound hole changed the resonant characteristics of the acoustic cavity, which fed back to the piezo itself, which then splashed back to the transistor and exceeded its Vce(max) rating. The Murata datasheet does warn against blocking the sound hole, and recommends at least 15 mm of clearance. Of course I found this out after the destruction.
Does anyone else have any similar experience of buzzer deaths? I'm sure I've blocked sound holes before and got away with it, but with this particular model (not a Murata, I should add, I've just cheekily quoted their datasheet because it's a good source) I managed to pop two in quick succession. I'd like to be able to use these things in the future with some confidence in their reliability.
Thank-you in advance for your valuable inputs.
[Diagram from Murata]
I guess me blocking the sound hole changed the resonant characteristics of the acoustic cavity, which fed back to the piezo itself, which then splashed back to the transistor and exceeded its Vce(max) rating. The Murata datasheet does warn against blocking the sound hole, and recommends at least 15 mm of clearance. Of course I found this out after the destruction.
Does anyone else have any similar experience of buzzer deaths? I'm sure I've blocked sound holes before and got away with it, but with this particular model (not a Murata, I should add, I've just cheekily quoted their datasheet because it's a good source) I managed to pop two in quick succession. I'd like to be able to use these things in the future with some confidence in their reliability.
Thank-you in advance for your valuable inputs.
