mosfet as switch

[lerameur]

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

 

[lerameur]

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

 

[lerameur]

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

 

[lerameur]

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

 

[lerameur]

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

 

[lerameur]

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

 

[lerameur]

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

 

[John Fields]

On Mon, 18 Aug 2008 14:24:14 -0700 (PDT), lerameur
<lerameur@yahoo.com> wrote:

On Aug 18, 4:21 pm, John Fields <jfie...@austininstruments.com> wrote:
On Mon, 18 Aug 2008 12:10:26 -0700 (PDT), lerameur



leram...@yahoo.com> wrote:
On Aug 18, 10:49 am, John Fields <jfie...@austininstruments.com
wrote:
But what are you trying to do?

JF

What I want to do is to be able to fully control by battery bank at a
distance. I have some batteries that are fully charged and others need
to be charged. I would like to switch over a specific battery from one
battery bank to another without moving it. So, in one of the case, I
would want to hook up an extra battery in parallel when in the battery
bank, therefore I need to hook up the positive to the bank positive
and the negative to the bank negative. I am having a bit of problem
hooking up two identical voltage.

B

---
I still don't really understand what you're trying to do.

Can you explain your application in detail?

JF

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.

---
That still makes no sense to me.

If V2, V3, and V4 are to be used, how do you plan to connect their
grounds to the load?

If what you're trying to do is have a bunch of batteries that are
being charged in one bank and another bunch of batteries that are
being discharged in another bank, then you could do it like this, with
relays, and isolate the load completely from the charger: (View in a
non-proportional font.)


+------+----------+-----------//--+
| | +---|------+---//---|------+-----+
| | | | | | | |
| O->| <-O O->| <-O O->| <-O |
| |K1A |K2A |KnA |
| O O O |
|+ |+ |+ |+ |+
[CHARGER] [BAT1] [BAT2] [BATn] [LOAD]
| | | | |
| O O O |
| |K1B |K2B |KnB |
| O->| <-O O->| <-O O->| <-O |
| | | | | | | |
| | +---|------+---//---|------+-----+
+------+----------+----------//---+

Is that what you have in mind, but with solid-state switches/relays
instead of mechanical relays?

JF

 

[Jamie]

lerameur wrote:

On Aug 16, 7:34 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

lerameur wrote:

hi,

I have two 12v batteries which I am hooking up in parallel using a
mechanical switch (via the ground).
I am attempting to swap the mechanical switch for a mosfet so I can
control them from a distance.
I tried to model in pspice but this is harder then I imagine. I tried
it experimentally, but when I hook up a iRFz44 , the batteries stays
in parallel no matter the voltage in the base. anyone has an idea to
overcome this.

B

If you can't show the circuit then please try to describe its
connections..
My guess is that you're using it incorrectly!.

This Mosfet has a body diode in it, which means if you apply
+ voltage on the source, it'll be there at the drain. And the
Gate is a voltage control device not a current device as you are using
in terms of (BASE). You should at least have a pull down R to ground so
that you keep the gate discharged!. IT's a very high Z input which can
maintain a charge. You also can damage it.

Since this component is a N channel device, you need to pull the
(-) terminal of the battery to common via the Drain connection of
the NMos and the Source goes to common..

The Gate will be switched on via what ever voltage needed.
I didn't look at all of the spec's

http://webpages.charter.net/jamie_5"


the circuit is really simple.
connection the ground of two batteries, the positives are not attached
to anything.
yes I could use an alligator clip and hook up the two grounds
together. But I would like to use a semiconductor. I would need some
sort of mosfet but when the gate is activated, it can let current flow
in both direction, is there anything on the market that can do this?

B
Are you saying you want to put these batteries in series ?

I think at this point you maybe better off using a relay..


http://webpages.charter.net/jamie_5"