I am using various kinds of low-end small Flight Controllers. While observing a buzzer waveform, I noticed a very large spike voltage. It can be easily prevented with a diode. I hope this post will be helpful.
A buzzer terminal of small FC is amplified by a transistor (such as MMBT3904 or KST14). When an electromagnetic buzzer (whether passive or active) is connected, a large spike voltage of almost 100V is generated with each switching.
This may cause a FC to malfunction, and also may destroy a transistor in the worst case, since it far exceeds “Absolute Maximum Ratings” of useing transistor.
By connecting a diode (such as 1S4) in parallel with a buzzer, a spike voltage could be easily prevented.