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I am a novice, and I'm playing around with SMD magnetic buzzers. For instance, the CUI CMT-322-65-SMT-TR.

In the datasheet they recommend something like this: enter image description here

After some Googling I learnt the diode is a flyback diode, which prevents the transistor from being damaged when power is cut.

My question is: how do I know which diode to use?

In this case, the +VDC powering the buzzer would be 3V. Do I need a regular, Zener or Schottky diode? Regardless of the type, what kind of characteristics should I then be looking for in this specific configuration?

This is an SMD project, but since I'm just experimenting I can also play around with through-hole diodes if you have any suggestions.

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    \$\begingroup\$ Your buzzer is magnetic, not piezo. Please correct your title. \$\endgroup\$ Dec 1, 2021 at 14:43

3 Answers 3

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Take a look at the data sheet: -

enter image description here

So what this tells you is: -

  • It's a magnetic device and not a piezo device
  • The rated voltage is 3 volts p-p typically
  • At the rated voltage the current consumption is 120 mA

Doublechecking the numbers, 50% of 3 volts divided by the typical coil resistance (12 Ω) is 125 mA peak current. Not far off so believable.

how do I know which diode to use?

Use a diode that is rated at a forward current of at least 125 mA. Maybe go for the inexpensive 1N400x series of diode. There isn't anything particularly onerous in this circuit that requires anything other than a standard diode but, if you have a Schottky diode to hand, that wouldn't be a problem either.

You should not attempt to run the +Vdc supply any higher than 4 volts for this type of buzzer hence, don't employ a 5 volt supply unless you put a resistor in series with the buzzer to limit that peak current to below ~120 mA.

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  • \$\begingroup\$ I recommend 1N4448 as they are faster. Probably not strictly required here over 1N00x but might as well. \$\endgroup\$
    – DKNguyen
    Dec 1, 2021 at 14:58
  • \$\begingroup\$ Thank you for the detailed reasoning and explanation. I learned a lot from this. \$\endgroup\$
    – peanutman
    Dec 1, 2021 at 15:11
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You just need a fast diode that operates in forward conduction which rules out Zeners. "Regular" PN diodes are typically for 50/60Hz rectification so can be slow because they do not need to be fast.

So could be a fast PN, Schottky, whatever. Schottky diodes are inherently faster than most but sometimes you can't find them in the required voltage or current ratings.

You could also use a low-value (1-10 Ohms probably) series resistor and ceramic cap (100nF-1uF probably) instead for an RC snubber and be just fine.

Make sure to learn why the flyback diode or snubber protects the transistor and you won't need to ask this question.

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  • \$\begingroup\$ Thank you for the info! This also helped me a lot, but sadly I can only pick one response as the "answer". \$\endgroup\$
    – peanutman
    Dec 1, 2021 at 15:12
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It hardly matters, however, you don't want to use a diode so absurdly large that it is slow to turn on. Zeners are inappropriate here.

Fast is good. Schottky diodes tend to be fast.

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