N-channel or P-channel Mosfets

[HappyHobit]

Hi All,

I'm building a motor controller for an electric bike. The circuit I found
uses a microcontroller, a 4N35 Opto-isolator and N-channel Mosfets. I like
micros and want to do voltage and current monitoring.

The problem is microcontroller has to turn the 4N35 ON to turn the
Mosfets OFF. I don't like that. If the 4N35 or the 5 volt supply fails
the
Mosfets turn on FULL.

I was thinking of using P-channel Mosfets. (And of course appropriate
circuit and logic changes)

Is there any prevailing reason to use N-channel rather than P-channel
Mosfets?

Thanks for any enlightenment you can provide.


Jay

 

[HappyHobit]

use an open collector buffer with a resistor tied to FET's voltage and use
this to drive the opto so it is on whenever the. FET voltage is on, even
if the micro is not present the opto will be on, FET off, surely you get
it?

Yes, I get it, but Why?

N-channels are more efficient, less Rd-on (on resistance), they use
electrons as the majority carriers not the less mobile holes, generally
they are cheaper and more readily available, I can go on.....

Thank you. Than answers my question.

Jay

 

[Hlrsr]

But 'holes' going one way are really just electrons going the other way.

Though the mobility (ì) of holes is less than the mobility of electrons thus
n-channel are "faster"

 

[Tater Schuld]

better read you theory books again, all of you

holes don't exist, they are just used to properly explain the missing
electrons.

for the application involved, it does not matter if your use hole flow or
electron flow

 

[Hlrsr]

We know that a hole is the absense of an electron, though it has an
_effective mass_

Look
http://en.wikipedia.org/wiki/Effective_mass

better read you theory books again, all of you

holes don't exist, they are just used to properly explain the missing
electrons.

for the application involved, it does not matter if your use hole flow or
electron flow