Buzzer Voltage and Current Waveforms

I have a buzzer circuit. Attached my schematics and the waveform.

Please have a look at the schematic attached. Also mentioned where I am measuring the values.

My questions :

1. I have marked the points in the circuit where I am measuring the voltage and the current. PWM pulse is given to the base of the transistor. I want to understand why the voltage waveform is like that and the current waveform is like that? Why is the voltage waveform Flat and the current waveform like spiked?

2. I would like to understand, only what will happen if I keep increasing the PWM pulse width at the base of the transistor. Please help me understand. (I don't write codes which is why I would not be able to check this by varying the PWM output coming from the Microcontroller to the base of the transistor)

Re: Buzzer Voltage and Current waveforms

Something doesn't look right.

The voltage should be square edged pulses and the current should have spikes at the same frequency. I can't see any voltage pulses so I assume it isn't PWM but a steady voltage.

The breaks in the current pulses don't make sense either, I suspect the LS800 is s buzzer with an internal oscillator so you would only be turning it on or off with the PWM rather than producing the sound from the PWM waveform.

Expanding the scope trace so we could see a few cycles of the waveform would help.

Brian.

Re: Buzzer Voltage and Current waveforms

Can you more details like
Which source are you using to drive PWM (Is it from any uController/Function generator) - what is the voltage level - scope capture shows voltage is 15V. you are driving 15v at the base of the transistor. If the base voltage(15V) is higher than collector voltage (12V) BJT will not saturate.
Give BJT & Buzzer part numbers atleast.

The voltage is a 12 V supply, I assume bypassed with bulk capacitors,
hence making it look like a Vsource. So there would be no, or very little,
change in it if the bypassing is effective.

Is the buzzer piezo ?


Regards, Dana.

Huh? Hundreds of mA into a little 12V piezo beeper??
Oh, is this to blast the high frequencies at kids to drive them away again? Its Kemo piezo beeper has a built-in transformer with an 8 ohms input.