Driving MOSFET from microcontroller (PIC)

Thread Starter

BrianK

Joined Jan 21, 2007
1
Hi,
I need to drive a STP75NF75 N channel MOSFET from the PWM signal produced from a PIC microcontroller. The frequency will be 10MHZ. What kind of driver circuit will I need between the PIC and the MOSFET? The input capcitance is listed as 3700pf. The PIC runs off 5 volts. The MOSFET will switch 12 volts. Does the gate volate need to be at 12 volts instead of 5?

Thanks for any ideas. I appreciate it.

Thanks,
Brian
 

hgmjr

Joined Jan 28, 2005
9,029
Hi,
I need to drive a STP75NF75 N channel MOSFET from the PWM signal produced from a PIC microcontroller. The frequency will be 10MHZ. What kind of driver circuit will I need between the PIC and the MOSFET? The input capcitance is listed as 3700pf. The PIC runs off 5 volts. The MOSFET will switch 12 volts. Does the gate volate need to be at 12 volts instead of 5?

Thanks for any ideas. I appreciate it.

Thanks,
Brian
Greetings Brian,

I am somewhat skeptical that you will have much luck trying to switch the MOSFET at 10MHz.

Is it possible that 10 MHz you are refering to is the clock speed at which the PIC is operating? The fastest PWM's that I am aware of are used in switching power supplies. These operate at 100's of KiloHertz.

In motor speed controllers, the operating frequency is in the range of several KiloHertz.

Do you mind devulging what your application is for a 10 MHz PWM signal?

Just Curious,
hgmjr
 

John Luciani

Joined Apr 3, 2007
477
I am somewhat skeptical that you will have much luck trying to switch the MOSFET at 10MHz.

Is it possible that 10 MHz you are refering to is the clock speed at which the PIC is operating? The fastest PWM's that I am aware of are used in switching power supplies. These operate at 100's of KiloHertz.
The low cost switching power supplies in consumer gear is in the 100's KHz put there
are many switching power supplies that are in the MHz range . www.vicr.com makes supplies high power supplies that are least 2MHz (possible 3 or 4).

Linear Technologies makes power supply controllers that switch up to 2MHz.
I use the LT3467ES6 (1.3MHz) in a uC power supply board. For a picture
of my power supply checkout the "Wall Transformer Power Supply" at

http://www.luciani.org/works-in-progress/works-in-progress-index.html

Refdes U91 is the controller IC.

(* jcl *)
---
www.luciani.org
 

John Luciani

Joined Apr 3, 2007
477
Hi,
I need to drive a STP75NF75 N channel MOSFET from the PWM signal produced from a PIC microcontroller. The frequency will be 10MHZ. What kind of driver circuit will I need between the PIC and the MOSFET? The input capcitance is listed as 3700pf. The PIC runs off 5 volts. The MOSFET will switch 12 volts. Does the gate volate need to be at 12 volts instead of 5?
You haven't said the current rating you require. You can get MOSFETs that will switch 10MHz but not the STP75N75. Look in the datasheet for switching time specifications.
Since you are only switching 12V you really do not need a 75V device. Look
for a 20V or 30V part.

You will get lower power dissipation if you can drive the gate at a higher Vgs.
If driving the gate at 10V is not convenient look for a logic level FET.
An excellent website for MOSFETs (and a wide variety of other semiconductors) is onsemi.com I have not seen a better search capability anywhere.

(* jcl *)

---
www.luciani.org
 
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