# Lorin EdwinP

2CommentsJoined July 29th, 2016

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• The reason you need the transformer is a matter of impedance. A piezoelectric element is rather high impedance, and very capacitive. In fact one generally treats them as a capacitor. So, a capacitor passes AC, but rejects DC. This fact, means that only the transitions in your square wave actually carry any power, so you're losing much of the power due to DC blocking. Further, piezos tend to dampen themselves mechanically due to a sharp resonance / antiresonance. So, here, the trick is that you're decoupling the capacitor (piezo) up off of ground and letting it couple at resonance with the inductive transformer winding. Think of a the way that a spring allows something to move more freely, even if it is tied to something quite heavy. If you use an audio transformer say 8ohm to 10kohm or ...

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The reason you need the transformer is a matter of impedance. A piezoelectric element is rather high impedance, and very capacitive. In fact one generally treats them as a capacitor. So, a capacitor passes AC, but rejects DC. This fact, means that only the transitions in your square wave actually carry any power, so you're losing much of the power due to DC blocking. Further, piezos tend to dampen themselves mechanically due to a sharp resonance / antiresonance. So, here, the trick is that you're decoupling the capacitor (piezo) up off of ground and letting it couple at resonance with the inductive transformer winding. Think of a the way that a spring allows something to move more freely, even if it is tied to something quite heavy. If you use an audio transformer say 8ohm to 10kohm or more, you can actually get some pretty impressive frequency ranges, play music through it, even vibrate an object (thin wood, metal plate)...

Can also use an inductor in parallel with piezo with ground & a transistor to drive it. You can find coils that will work in old phones, power supplies, AV baluns, etc. You just need inductance to optimize current across capacitor over time.