Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
(OP)
Hello,
Goal: Drive a cep_2242 piezo buzzer from a 3.3V FPGA output. Driving direct from FPGA does not generate the required sound volume, not surprising considering the buzzer operating voltage is 3-16 Vdc (7mA max at 12V).
I would like to use an integrated load switch, so I can provide 12V to the buzzer and on/off with the FPGA output.
My question is: Can someone recommend a load switch which will work with the 7mA max current drawn by the buzzer?
Maybe similiar to the FDC6324L (Vin 3-20V range / on 1.5-8V) but with a much lower load current minimum when on.
Thank you,
Chris
Goal: Drive a cep_2242 piezo buzzer from a 3.3V FPGA output. Driving direct from FPGA does not generate the required sound volume, not surprising considering the buzzer operating voltage is 3-16 Vdc (7mA max at 12V).
I would like to use an integrated load switch, so I can provide 12V to the buzzer and on/off with the FPGA output.
My question is: Can someone recommend a load switch which will work with the 7mA max current drawn by the buzzer?
Maybe similiar to the FDC6324L (Vin 3-20V range / on 1.5-8V) but with a much lower load current minimum when on.
Thank you,
Chris





RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
Amen.
Or perhaps a 2N2907 if you wish to 'reverse' the circuit.
Good thing that Dan got here before someone recommended a single board computer.
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
I added a 10K pull-down from the base to cover FPGA reset, where the IO pin floats. As suggested, I used a 10K resistor between the 3.3V FPGA output and the 2N3904 NPN base to set collector current. DRIVEPOWER (see diagram) varies from 5V-12V.
If anything doesn't look right, please advise.
I was a little surprised the buzzer (cep_2242, max 7mA at 12V) does not require a current limiting resistor (as an LED does). I tested it directly with a 12V supply seemingly without issue.
Happy Thanksgiving,
Chris
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
To be honest, I'd probably put the current-set resistor in the emitter, not the base... otherwise you're counting on the beta of the transistor to be constant from unit to unit (and to be fair, they generally are pretty good, even with the cheapest of transistors).
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
> current is okay with that).
Could you be more descriptive? Why would you make the
pull-down 100k instead of 10K?
Thanks!
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
From a design standpoint, it's also wasteful of power, losing 50% of your pin current through a pull-down. Not a big deal here, but add enough drivers like that and the power adds up quickly.
Just make sure whatever you set it at can handle the leakage current of the pin without dragging the base high enough to turn it on.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
> up as half-voltage at the base of the transistor... a
> 3.3V FPGA will drive the transistor base to 1.65V
> (actually, a bit less considering the amount of current
> into the base of the transistor).
Good point, the MMBT3904 datasheet lists the Base-Emitter
Saturation Voltage at 0.95V max in the "ON characteristics"
section. So it seems we are OK with the half divider, as
the voltage exceeds the 0.95V required to turn ON the
amplifier.
Any reason to believe this is *not* enough margin for the
amplifier to turn on?
Thanks.
RE: Drive a piezo buzzer (cep_2242) from a 3.3V FPGA output?
Dan - Owner

http://www.Hi-TecDesigns.com