Regarding Buzzer Driving Circuit

[sakibnaz]

Hi there. I am designing a Buzzer circuit and I'll be glad to have some advise if my design is Ok.

My Buzzer is "FUET-8540-3.6V" with below specification:

I choose NPN "BC817-40-7-F" considering HFE more than 200.

I put RL = 33 Ohm as Coil Resistor if Buzzer is 16 Ohm. So total effective will be ~50 Ohm resistor for Load. So 5V / 50Ohm = 100mA Buzzer Current.

Also please advise if the RB 180 Ohm is Ok for my application?


Thanks.

 

[FvM]

I'd use 470 ohms to 1k for Rb.

 

[sakibnaz]

Ok ... can you share the calculation for this RB selection?

 

[KlausST]

Hi,

a rule of thumb is to use
I_B = 1/20 ... to
I_B = I_C/10

so 5mA ... 10mA of base current should be sufficient.

Klaus

 

[Akanimo]

The transistor may have minimum Vce(sat) of around 0.2V.
So \(Rc_{total}=\frac{5-0.2}{100mA}=48ohm\)
\(Rc_{ext}=48-(16-3)=35ohm\)
That's for \(Ic=100mA\).
33ohm allows \(Ic>100mA\). I would recommend Rc of 47ohm.
No need to bother about Rb. \(Ib=\frac{V_b-V_{be}}{R_b}\). With 180ohm, it's just a maximum of about 13mA of Ib. 220ohm will give you about 11mA max. 330ohm allows about 7.3mA max. You could still pick a higher Rb from this list. This will further reduce Ib as recommended in previous posts.