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BC546 transistor failure

jonathang

Hi All,

I am new to the platform please excuse me if I am going about this in the incorrect way, I am a hobbyist and have designed a RFID module that has a 485-line driver to communicate with a master device. I have ordered the bords from JLC and assembled the unit. I have a 12dcv supply, I have two 270E 1/4W resistors in parallel to assist with limiting the strain on the 7805 linear regulator, I since have discovered that the resistors restrict too much current and the Arduino was suffering possible brownout events.

What I am struggling with is the failure of the BC546 bjt driving the active buzzer, the buzzer is rated 8-15VDC 30mA, the failure starts as a static noise coming from the buzzer when the MCU pin is set to low and eventually the bjt fails and the buzzer keeps on buzzing.

I would appreciate some advice my errors,

Regards

image

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  • Which type of buzzer are you using? Magnetic or piezoelectric.

    If you have a magnetic buzzer, you have to incorporate a flyback diode across its terminals. This diode will mitigate the voltage spikes (flyback) that occur when the BJT switch is turned off. These spikes can damage the transistor if left unchecked.

    If you have a piezoelectric buzzer you can add a discharge resistor across the buzzer as piezoelectric buzzers hold a charge momentarily due to their capacitive nature. Maybe you have to redesign your driver circuit maybe adding a buffer.

    I am not an expert on the subject, these are things that I have seen in other circuits but I think it will help the discussion.

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  • Which type of buzzer are you using? Magnetic or piezoelectric.

    If you have a magnetic buzzer, you have to incorporate a flyback diode across its terminals. This diode will mitigate the voltage spikes (flyback) that occur when the BJT switch is turned off. These spikes can damage the transistor if left unchecked.

    If you have a piezoelectric buzzer you can add a discharge resistor across the buzzer as piezoelectric buzzers hold a charge momentarily due to their capacitive nature. Maybe you have to redesign your driver circuit maybe adding a buffer.

    I am not an expert on the subject, these are things that I have seen in other circuits but I think it will help the discussion.

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