Fixing an ultrasonic vaporizer

Thread Starter

cmartinez

Joined Jan 17, 2007
7,334
My sister brought me one of those ultrasonic small tabletop herbal vaporizers in the hope that I could fix it (they're not vaporizers, btw... they're really atomizers) because the cleaning lady dropped it from a height of less than 4 inches while it was turned on, and the thing stopped working and she wasn't able to even turn it on again afterwards.

Anyway... she squarely places the blame on the young girl.. but I told her that was bonkers and to bring me the thing so I could take a closer look at it.

So what I did was disassemble it and take a closer look at its circuit. And everything seemed fine. No burnt nor broken traces nor obviously blown components. I also cleaned its piezo element carefully. But when I checked its power supply (which is a 24C@0.5A wall wart) with my multimeter, the thing was dead.

That was the "aha" moment for me... I told her to please stop blaming the girl and to simply buy another wall wart of the same output voltage (although I recommended one that could deliver at least 1 amp ... the more the merrier) and assured her that the thing would immediately start working again.

... that's when something clicked in my head: the device was dropped form a short distance... but piezo elements work both ways ... that is, they are transducers... they can either receive power and convert it into mechanical vibrations, but they can also be subject to mechanical vibrations and in turn convert them into power...

Is it possible that such a mild shock made the piezo emit an electric surge that then flowed back into the main circuit and then went further down into the power supply itself? ... If that's what happened, then both the wall wart and the controller circuit could be fried ... I find that very hard to believe, but it's not entirely impossible ... is it?

Unfortunately, I do not have a power supply capable of delivering 24V to test the device... so she's just going to have to spend $12.00 bucks on a new one and hope that's the only thing that's wrong with it.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,334
Update

My sister tested the device using a wall wart from an identical device loaned from one of her friends, and lo and behold! ... the thing came back to life and started working as if nothing happened!

So, what are the odds of the power supply malfunctioning at the exact moment that the device (but not the power supply) was slightly knocked? ... I'm still wondering if the piezo element had something to do with it. But if it did, then both the power supply and the controller circuit should have been affected, shouldn't it?
 

KeithWalker

Joined Jul 10, 2017
1,789
You are correct. It is quite likely that the mechanical shock caused the piezo-electric element to generate a high voltage pulse that temporarily overloaded the output stage, causing the supply to blow. Give yourself a pat on the back. It really is surprising how many IEEs do not fully understand that piezo-electric devices work both ways. :)
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,334
You are correct. It is quite likely that the mechanical shock caused the piezo-electric element to generate a high voltage pulse that temporarily overloaded the output stage, causing the supply to blow. Give yourself a pat on the back. It really is surprising how many IEEs do not fully understand that piezo-electric devices work both ways. :)
Ok... so my next question is: why wasn't the rest of the circuit affected? ... the piezo is driven by a FET, which in turn is driven by an MCU ... how come those two rather delicate components were not affected?
 

KeithWalker

Joined Jul 10, 2017
1,789
Ok... so my next question is: why wasn't the rest of the circuit affected? ... the piezo is driven by a FET, which in turn is driven by an MCU ... how come those two rather delicate components were not affected?
I don't have a copy of the schematic so I have no idea. Just consider yourself lucky and be happy to be a hero for the day.
 
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