# Piezo Buzzer Coil or Resistor oscilator

Discussion in 'The Projects Forum' started by Gabriel Pianez, Oct 12, 2016.

1. ### Gabriel Pianez Thread Starter New Member

Oct 2, 2016
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Hello, I found two types of working with piezo like a buzzer, in the first case, we use only resistor, when turn ON Circuit, I have my transistor off, With Vc=VDC, When Piezo Sends a feedback voltage, we have a saturation in transistor, My Vc = 0.2 ( aproximated) the piezo don't stretches and feedback voltage = Zero.

But, how it's works using an inductor ? When we saturate the transistor, the coil try to maintain the current throught the circuit, and a -EMF voltage appears and polarize in reverse my base and cutoff the transistor, this cause a oscilation in my piezo ?

Is There Any Difference in efficiency of each circuit?

2. ### AnalogKid Distinguished Member

Aug 1, 2013
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1,297
In both circuits, when the transistor turns off the collector load pulls the collector pin high toward Vcc. But with the inductor, there is an "inductive kick" caused by the collapsing magnetic field. This is also called a flyback circuit. The result is that the collector can go significantly *above* Vcc, increasing the voltage swing across the piezo element, increasing the loudness. But, the flyback voltage can be large enough to destroy the transistor, so the parts must be chosen carefully.

ak

3. ### Gabriel Pianez Thread Starter New Member

Oct 2, 2016
10
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The fluback voltage will be large even with the current flowing throught at piezo ? i Think thats voltage would be smallest, because the current can flow decreasing di/dt.

4. ### AnalogKid Distinguished Member

Aug 1, 2013
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Depends on the inductor value, construction, and Q, and the operating frequency.

ak

Gabriel Pianez likes this.

Oct 2, 2016
10
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Thanks!