A quick note, I had asked a similar question around driving an external buzzer previously: Driving external piezo buzzers

This is a question in regards to driving an internal buzzer, so not a transducer. The part number for the buzzer is SMA-21-S.

Here is what I had in mind:

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So drive the FET through an MCU and buzzer turns on and vice versa.

The specification for the buzzer says :

enter image description here

Supply is 3.8mA. In the event the gate voltage is high, Buzzer2_N is at roughly gnd potential (ignoring Rdson.) You will then have 24V on the positive terminal and 0V on the negative terminal. Buzzer is on.

When the gate is open, you have 24V on the + and Buzzer2_N is at 24V as well since no path for current flow, so the buzzer is off as no potential difference.

Is this correct? Would this circuit work? Should I improve it or change something here? Is there anything in regards to layout with buzzers I should be aware of? Are these electrically noisy?

  • \$\begingroup\$ A few tips: "internal-drive buzzer" would make more sense than "internal buzzer" which just implies a buzzer inside something. "When the gate is open, ..." You shouldn't leave an FET gate "open" (disconnected). I think you mean "pulled low". \$\endgroup\$
    – Transistor
    Oct 29, 2021 at 10:50

1 Answer 1


The circuit can work as intended but it still needs some improvements:

  • R44 should be removed because as long as the MOSFET is kept turned on (i.e. buzzer is active) that resistor will dissipate a power of approximately 0.6W for no reason.
  • R46 does not have to be that large. An 10k-ish resistance is okay.
  • \$\begingroup\$ Thank you for the suggestions! However, i thought a piezo buzzer is modelled as capacitive and not inductive? \$\endgroup\$
    – Hasman404
    Oct 29, 2021 at 10:31
  • \$\begingroup\$ Does it hurt for R46 to be that large? \$\endgroup\$ Oct 29, 2021 at 10:34
  • \$\begingroup\$ Also why do you think the buzzer is inductive? This is a buzzer (integrated oscillator+transducer) not just a transducer. I infer that from the fact the asker specifically said it's not a transducer. OP can correct this if wrong. \$\endgroup\$ Oct 29, 2021 at 10:35
  • \$\begingroup\$ @user253751 ops, I missed that part. Thanks for correcting. \$\endgroup\$ Oct 29, 2021 at 10:56

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