Electronics (alt.electronics)

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HappyHobit
 
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Default N-channel or P-channel Mosfets

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





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Dleer
 
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Default N-channel or P-channel Mosfets

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?

If a high was coming from the micro you will need to invert this logic, or
use an inverting OC buffer. OC buffers accept TTL on their input but can
connect to other DC votages on their output. Follow spec sheet for the
buffer's sink current to size resistor as well as opto drive current.
Basically the sink current robs the opto's turn-on current when the buffer's
output goes low.

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.....

DR

"HappyHobit" wrote in message
...
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







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Geoff
 
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Default N-channel or P-channel Mosfets

HappyHobit wrote:
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.


I wouldn't worry about it too much - equally your wheel might fall off.. If
you are preoccupied thinking aboyut things like this you will probably get
hit by a bus.

geoff


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HappyHobit
 
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Default N-channel or P-channel Mosfets


"Dleer" wrote in message
. ..

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


  #5   Report Post  
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Geoff
 
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Default N-channel or P-channel Mosfets

Dleer wrote:

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.....


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

geoff




  #6   Report Post  
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Hlrsr
 
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Default N-channel or P-channel Mosfets


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

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


  #7   Report Post  
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Jasen Betts
 
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Default N-channel or P-channel Mosfets

On 2006-05-18, Geoff wrote:
Dleer wrote:

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.....


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


no. holes have positive mass, behave differently to electrons in the
presence of a magnetic field, etc...



geoff




--

Bye.
Jasen
  #8   Report Post  
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Tater Schuld
 
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Default N-channel or P-channel Mosfets

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

"Jasen Betts" wrote in message
...
On 2006-05-18, Geoff wrote:
Dleer wrote:

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.....


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


no. holes have positive mass, behave differently to electrons in the
presence of a magnetic field, etc...



geoff




--

Bye.
Jasen



  #9   Report Post  
Posted to alt.electronics
Hlrsr
 
Posts: n/a
Default N-channel or P-channel Mosfets

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


"Tater Schuld" wrote in message
...
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

"Jasen Betts" wrote in message
...
On 2006-05-18, Geoff wrote:
Dleer wrote:

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.....

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

way.

no. holes have positive mass, behave differently to electrons in the
presence of a magnetic field, etc...



geoff




--

Bye.
Jasen





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