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Sci.Electronics.Basics -> mosfet as switch
There are 29 messages in this thread.
You are currently looking at messages 20 to 29.
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Author: lerameurDate: 22:09 18-08-08
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On Aug 18, 8:09 pm, John Popelish <jpopel...@rica.net> wrote:
> lerameur wrote:
> > I posted the circuit on the following link:
> >http://www3.sympatico.ca/lerameur/batteries/multiple_grounds.jpg
>
> > The idea is to disable M1 so only battery V2 V3 and V4 are used.
>
> The problem with that design is the internal diode that
> parallels each MOSFET. For one direction of current, each
> MOSFET will conduct through that diode, even if the gate is
> reverse biased. Even if you reconfigure this parallel
> battery arrangement to have each battery negative connect to
> a single common node node (instead of a ladder structure)
> you still have to account for both battery charge and
> discharge current (if the batteries will be charged in
> place). That requires a pair of MOSFETs in series, an
> N-channel and a P-channel, so that each one blocks for the
> other when its internal diode is forward biased.
>
> The you have to get the gate biasing right.
>
> --
> Regards,
>
> John Popelish
I have been reading this pdf from above
http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
what is confusing is on page 10 (4-10)
THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
pointing to both direction, this seems wrong, I thought current can
only flow in one direction, is this pdf right?
B
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Author: John PopelishDate: 22:25 18-08-08
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lerameur wrote:
> I have been reading this pdf from above
> http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
> what is confusing is on page 10 (4-10)
> THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
> pointing to both direction, this seems wrong, I thought current can
> only flow in one direction, is this pdf right?
I see only 6 pages in that data sheet, but the channel of a
MOSFET can conduct current in either direction. The body
diode in parallel with the channel can conduct only in one
direction.
--
Regards,
John Popelish
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Author: lerameurDate: 22:26 18-08-08
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On Aug 18, 8:09 pm, John Popelish <jpopel...@rica.net> wrote:
> lerameur wrote:
> > I posted the circuit on the following link:
> >http://www3.sympatico.ca/lerameur/batteries/multiple_grounds.jpg
>
> > The idea is to disable M1 so only battery V2 V3 and V4 are used.
>
> The problem with that design is the internal diode that
> parallels each MOSFET. For one direction of current, each
> MOSFET will conduct through that diode, even if the gate is
> reverse biased. Even if you reconfigure this parallel
> battery arrangement to have each battery negative connect to
> a single common node node (instead of a ladder structure)
> you still have to account for both battery charge and
> discharge current (if the batteries will be charged in
> place). That requires a pair of MOSFETs in series, an
> N-channel and a P-channel, so that each one blocks for the
> other when its internal diode is forward biased.
>
> The you have to get the gate biasing right.
>
> --
> Regards,
>
> John Popelish
I have been reading this pdf from above
http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
what is confusing is on page 10 (4-10)
THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
pointing to both direction, this seems wrong, I thought current can
only flow in one direction, is this pdf right?
B
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Author: lerameurDate: 22:27 18-08-08
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On Aug 18, 10:25 pm, John Popelish <jpopel...@rica.net> wrote:
> lerameur wrote:
> > I have been reading this pdf from above
> >http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
> > what is confusing is on page 10 (4-10)
> > THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
> > pointing to both direction, this seems wrong, I thought current can
> > only flow in one direction, is this pdf right?
>
> I see only 6 pages in that data sheet, but the channel of a
> MOSFET can conduct current in either direction. The body
> diode in parallel with the channel can conduct only in one
> direction.
>
> --
> Regards,
>
> John Popelish
Sorry , made a copy and paste mistake: this is the link:
http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
B
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Author: lerameurDate: 22:33 18-08-08
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On Aug 18, 10:25 pm, John Popelish <jpopel...@rica.net> wrote:
> lerameur wrote:
> > I have been reading this pdf from above
> >http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
> > what is confusing is on page 10 (4-10)
> > THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
> > pointing to both direction, this seems wrong, I thought current can
> > only flow in one direction, is this pdf right?
>
> I see only 6 pages in that data sheet, but the channel of a
> MOSFET can conduct current in either direction. The body
> diode in parallel with the channel can conduct only in one
> direction.
>
> --
> Regards,
>
> John Popelish
Sorry , made a copy and paste mistake: this is the link:
http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
B
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Author: lerameurDate: 22:35 18-08-08
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On Aug 18, 10:27 pm, lerameur <leram...@yahoo.com> wrote:
> On Aug 18, 10:25 pm, John Popelish <jpopel...@rica.net> wrote:
>
>
>
> > lerameur wrote:
> > > I have been reading this pdf from above
> > >http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
> > > what is confusing is on page 10 (4-10)
> > > THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
> > > pointing to both direction, this seems wrong, I thought current can
> > > only flow in one direction, is this pdf right?
>
> > I see only 6 pages in that data sheet, but the channel of a
> > MOSFET can conduct current in either direction. The body
> > diode in parallel with the channel can conduct only in one
> > direction.
>
> > --
> > Regards,
>
> > John Popelish
>
> Sorry , made a copy and paste mistake: this is the
link:http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
>
> B
I also made the schematic on page 10:
http://www3.sympatico.ca/lerameur/batteries/page10.jpg
I need to raise the voltage above 26v at the gate for it to conduct.,
as Vg needs to be higher.
IS the tutorial off ?
B
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Author: lerameurDate: 22:40 18-08-08
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On Aug 18, 10:27 pm, lerameur <leram...@yahoo.com> wrote:
> On Aug 18, 10:25 pm, John Popelish <jpopel...@rica.net> wrote:
>
>
>
> > lerameur wrote:
> > > I have been reading this pdf from above
> > >http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf
> > > what is confusing is on page 10 (4-10)
> > > THEY PUT 2 N-CHANNEL MOSFET back to back, with an arrow with current
> > > pointing to both direction, this seems wrong, I thought current can
> > > only flow in one direction, is this pdf right?
>
> > I see only 6 pages in that data sheet, but the channel of a
> > MOSFET can conduct current in either direction. The body
> > diode in parallel with the channel can conduct only in one
> > direction.
>
> > --
> > Regards,
>
> > John Popelish
>
> Sorry , made a copy and paste mistake: this is the
link:http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
>
> B
I also made the schematic on page 10:
http://www3.sympatico.ca/lerameur/batteries/page10.jpg
I need to raise the voltage above 26v at the gate for it to conduct.,
as Vg needs to be higher.
IS the tutorial off ?
B
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Author: John PopelishDate: 23:30 18-08-08
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Author: John PopelishDate: 23:37 18-08-08
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lerameur wrote:
> I also made the schematic on page 10:
> http://www3.sympatico.ca/lerameur/batteries/page10.jpg
> I need to raise the voltage above 26v at the gate for it to conduct.,
> as Vg needs to be higher.
> IS the tutorial off ?
In this schematic, you have not provided any way for the
seriesed MOSFETs to see ant gate voltage but zero (or to be
floating).
To see the switching you desire, put a pulsed voltage source
from the common source node between the two MOSFETs to
their common gate node.
Once you see them working (assuming the way it works is what
you are looking for), we can figure out how to do this
without a floating pulse source.
The schematic on page 10 of the
PDF is not the actual circuit inside the package, but only a
conceptual one. It shows what the outside world sees.
--
Regards,
John Popelish
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