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
    10
    0
    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?
    coil.png
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,538
    1,251
    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
    0
    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
    4,538
    1,251
    Depends on the inductor value, construction, and Q, and the operating frequency.

    ak
     
    Gabriel Pianez likes this.
  5. Gabriel Pianez

    Thread Starter New Member

    Oct 2, 2016
    10
    0
    Thanks!
     
Loading...