Driving a Magnetic Buzzer

[Luchik]

Background:
I want to drive a magnetic buzzer from a 3V source.
I use a BJT and a microcontroller connected to the BJT's Base pin. The microcontroller is also powered by the 3V source.
A square wave of 50% duty is generated by the microcontroller in order to drive the buzzer.


Now to my problem:
Some people say that I have a problem with the driving voltage, since the BJT will take about ~0.2V of the buzzer voltage, leaving ~2.8V for producing sound. I am considering whether a design change is necessary or not. Also, I prefer using a transistor that is already in the BOM (I have a NPN: PDTC123JT and a PMOS: DMP2100U).

Questions:
1. Should I use a MOSFET instead of BJT? Will it really help?
2. I noticed (in other designs) that a buzzer is always toggled to GND and not to VCC. Why is that?
    I'm thinking about using a PMOS and changing the design. What do you think?
3. Is the 0.2V voltage drop critical to performance?

Buzzer Datasheet:
http://www.quartz1.com/price/techdata/BOT-03D.pdf

Transistor Datasheet:
http://www.nxp.com/documents/data_sheet/PDTC123J_SER.pdf

Suggested PMOS:
http://www.diodes.com/_files/datasheets/DMP2100U.pdf

[leeatljs]

The voltage rating of the buzzer is 2-4V so you are well in there.
I notice the buzzer will draw about 100mA, that transistor is rated at 100mA.
IMHO you will need a beefier transistor, the 2N7002 would do nicely.

[Zero999]

1) Either a MOSFET of BJT will work. BJTs tend to be better at lower voltages though.

2) The 0V is often switched because it can be done with NPN/NMOS devices which are easier to get hold of and cost less for the same rating PNP/PMOS device. You can use PMOS if you like but it will have a higher on resistance than an NMOS device with everythinh else being equal.

3) It won't make much difference.

[Whales]

1 and 3) The best thing to do is try it.  These parts should be cheap (in comparison to your microcontroller).

2) Sometimes it's convenient to turn it on and off in reverse.  If you have no reason to do so, then there is no difference other than P-type parts generally being more expensive (as Hero999 states).