Driving a mosfet with a microcontroller

Driving a mosfet with a microcontroller#86538

By jeanseb - Sat Dec 05, 2009 6:05 pm

- Sat Dec 05, 2009 6:05 pm #86538

Hi,

I need to control the power supply of a couple of devices at about 400mA. I've been looking at what is done on the MCB2300 from Kiel:

http://www.keil.com/mcb2300/mcb2300-schematics.pdf (page 3)

They use a mosfet to control the supply of the SD card. However, they do not interface the mosfet directly to the microcontroller, they use a bipolar in between...

Anybody could explain why? Any way to interface directly with a mosfet? I really want to keep the part number down.

Thanks!
Jean

#86539

By SpinDrah - Sat Dec 05, 2009 6:08 pm

- Sat Dec 05, 2009 6:08 pm #86539

look into logic level mosfets.

#86543

By jeanseb - Sat Dec 05, 2009 6:47 pm

- Sat Dec 05, 2009 6:47 pm #86543

SpinDrah wrote:look into logic level mosfets.

Hi,
Thank you for the answer. How would you interface a logic level mosfet to a microcontroller?

Pull up connected to the source, source directly connected to output of the microntroller?

Thnaks!

#86546

By Vraz - Sat Dec 05, 2009 8:10 pm

- Sat Dec 05, 2009 8:10 pm #86546

My best guess is that the bipolar is there to create an open-collector output so they can swing the P-MOSFET from GND to 3.3v. At such low voltage levels, getting good rail-to-rail voltage is important. However, I would have thought they could have eliminated the bipolar and just used software to create an open-collector output. Voltage-low for the 2378 is only 0.18V which seems plenty low for that MOSFET.