mosfet as switch

L

lerameur

Guest
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
 
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
Click to expand...
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"
 
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"
Click to expand...
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
 
On Aug 16, 9:03 pm, lerameur <leram...@yahoo.com> 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
Click to expand...
I think it is called a UJT, just need to find one in pspice...

B
 
On 2008-08-17, lerameur <lerameur@yahoo.com> 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.


the circuit is really simple.
connection the ground of two batteries, the positives are not attached
to anything.
Click to expand...
Batteries connected like that will do nothing, more details would help.

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?
Click to expand...
MOSFETs will do that they just have that annoying body diode that
makes them always conduct (like a diode) in the backwards direction.

you may be able to escape this problem by connecting two back-to
back.

connect the gates together and the drains, then connect the sources
to the batteries and the gates to your control signal.

Bye.
Jasen
 
On Aug 16, 10:34 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
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"
Click to expand...
two grounds together, that would be parallel, But the UJT is taking
too much current just to enable it. The problem is that when I put a
MOsfet with source on one grounds and the drain on the other ground,
the batteries are in parallel. no matter what the gate voltage is...

B
 
On Aug 17, 5:34 am, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
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"
Click to expand...
Remember Occam's razor.

Don't use a transistor when a switch will do; don't use an IC when a
transistor will do........
 
On Sun, 17 Aug 2008 03:36:20 -0700 (PDT), lerameur
<lerameur@yahoo.com> wrote:

On Aug 16, 10:34 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
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"

two grounds together, that would be parallel, But the UJT is taking
too much current just to enable it. The problem is that when I put a
MOsfet with source on one grounds and the drain on the other ground,
the batteries are in parallel. no matter what the gate voltage is...
Click to expand...
---
Assuming you want to drive some sort of load, this should do it:

Version 4
SHEET 1 1268 944
WIRE -32 48 -352 48
WIRE 144 48 -32 48
WIRE 320 48 144 48
WIRE -352 112 -352 48
WIRE -32 128 -32 48
WIRE 144 128 144 48
WIRE -528 256 -592 256
WIRE -400 256 -528 256
WIRE -192 256 -400 256
WIRE -592 288 -592 256
WIRE 320 288 320 48
WIRE -528 336 -528 256
WIRE -352 336 -352 192
WIRE -192 336 -192 256
WIRE -400 352 -400 256
WIRE -32 448 -32 208
WIRE 144 448 144 208
WIRE -528 496 -528 416
WIRE -400 496 -400 400
WIRE -400 496 -528 496
WIRE -352 496 -352 416
WIRE -192 496 -192 416
WIRE -192 496 -352 496
WIRE -128 496 -192 496
WIRE -96 496 -128 496
WIRE 240 496 208 496
WIRE -128 592 -128 496
WIRE 240 592 240 496
WIRE 240 592 -128 592
WIRE -32 656 -32 544
WIRE 144 656 144 544
WIRE 144 656 -32 656
WIRE 320 656 320 368
WIRE 320 656 144 656
FLAG -592 288 0
SYMBOL voltage -528 432 R180
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 0 1E-6 1E-6 1 2)
SYMBOL sw -352 320 R0
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S2
SYMBOL npn -96 544 M180
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL voltage -32 112 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL res 304 272 R0
SYMATTR InstName R2
SYMATTR Value 24
SYMBOL res -208 320 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -368 96 R0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL voltage 144 112 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 12
SYMBOL npn 208 544 R180
SYMATTR InstName Q2
SYMATTR Value 2N2222
TEXT -720 528 Left 0 !.model SW SW(Ron=.01 Roff=10Meg Vt=0.5Vh=0)
TEXT -712 488 Left 0 !.tran 0 10 0


But what are you trying to do?

JF
 
On Mon, 18 Aug 2008 12:10:26 -0700 (PDT), lerameur
<lerameur@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
Click to expand...
---
I still don't really understand what you're trying to do.

Can you explain your application in detail?

JF
 
On Aug 18, 10:49 am, John Fields <jfie...@austininstruments.com>
wrote:
On Sun, 17 Aug 2008 03:36:20 -0700 (PDT), lerameur



leram...@yahoo.com> wrote:
On Aug 16, 10:34 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
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"

two grounds together, that would be parallel, But the UJT is taking
too much current just to enable it. The problem is that when I put a
MOsfet with source on one grounds and the drain on the other ground,
the batteries are in parallel. no matter what the gate voltage is...

---
Assuming you want to drive some sort of load, this should do it:

Version 4
SHEET 1 1268 944
WIRE -32 48 -352 48
WIRE 144 48 -32 48
WIRE 320 48 144 48
WIRE -352 112 -352 48
WIRE -32 128 -32 48
WIRE 144 128 144 48
WIRE -528 256 -592 256
WIRE -400 256 -528 256
WIRE -192 256 -400 256
WIRE -592 288 -592 256
WIRE 320 288 320 48
WIRE -528 336 -528 256
WIRE -352 336 -352 192
WIRE -192 336 -192 256
WIRE -400 352 -400 256
WIRE -32 448 -32 208
WIRE 144 448 144 208
WIRE -528 496 -528 416
WIRE -400 496 -400 400
WIRE -400 496 -528 496
WIRE -352 496 -352 416
WIRE -192 496 -192 416
WIRE -192 496 -352 496
WIRE -128 496 -192 496
WIRE -96 496 -128 496
WIRE 240 496 208 496
WIRE -128 592 -128 496
WIRE 240 592 240 496
WIRE 240 592 -128 592
WIRE -32 656 -32 544
WIRE 144 656 144 544
WIRE 144 656 -32 656
WIRE 320 656 320 368
WIRE 320 656 144 656
FLAG -592 288 0
SYMBOL voltage -528 432 R180
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 0 1E-6 1E-6 1 2)
SYMBOL sw -352 320 R0
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S2
SYMBOL npn -96 544 M180
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL voltage -32 112 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL res 304 272 R0
SYMATTR InstName R2
SYMATTR Value 24
SYMBOL res -208 320 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -368 96 R0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL voltage 144 112 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 12
SYMBOL npn 208 544 R180
SYMATTR InstName Q2
SYMATTR Value 2N2222
TEXT -720 528 Left 0 !.model SW SW(Ron=.01 Roff=10Meg Vt=0.5Vh=0)
TEXT -712 488 Left 0 !.tran 0 10 0

But what are you trying to do?

JF
Click to expand...
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
 
On Sat, 16 Aug 2008 15:26:36 -0700 (PDT), lerameur
<lerameur@yahoo.com> 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
Click to expand...
I'm not sure I fully understand what your trying to do,but if your
switching between batteries you should use a bidirectional switch.
This stops body diode conduction of the FET.

http://i33.tinypic.com/ddm9ap.png

I dont know your load but here is a pretty good PFET if it's beefy
enough for you.

http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf

You can get ten at Digikey for a little over Ten bucks.You will also
need a mosfet driver.

Here some reading for mosfets. 100 page PDF from fairchild .

http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
 
On Mon, 18 Aug 2008 22:15:22 GMT, Hammy <spamme@hotmail.com> wrote:

On Sat, 16 Aug 2008 15:26:36 -0700 (PDT), lerameur
lerameur@yahoo.com> 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

I'm not sure I fully understand what your trying to do,but if your
switching between batteries you should use a bidirectional switch.
This stops body diode conduction of the FET.

http://i33.tinypic.com/ddm9ap.png
Click to expand...
Made a mistake in my drawing.
Those two mosfets should be connected source to source.

I dont know your load but here is a pretty good PFET if it's beefy
enough for you.

http://www.fairchildsemi.com/ds/FD%2FFDD4141.pdf

You can get ten at Digikey for a little over Ten bucks.You will also
need a mosfet driver.

Here some reading for mosfets. 100 page PDF from fairchild .

http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
Click to expand...
 
On Aug 18, 1:21 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
Click to expand...


Trying not to get blown up by his lead-acid battery bank? ;-)

Michael
 
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
Click to expand...
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.

B
 
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.
Click to expand...
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
 
lerameur wrote:
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.

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?
Click to expand...
I am the one who made a mistake. You need two MOSFETs, so
that you can point a body diode each way, so that one or the
other blocks current, regardless of the current direction.
They can both be N-channel, both P-channel, or one P and one
N-channel, as long as the body diodes are pointing both
ways. The choice of type depends on which way the gate
biasing is most convenient.

That the current can go both ways is exactly the problem.
You get conduction through the channel (in either direction)
in parallel with the body diode, but one or the other MOSFET
must have a body diode reverse biased if the pair is to be
an open circuit when the MOSFETs are both off.

--
Regards,

John Popelish
 
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?
Click to expand...
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
 
lerameur wrote:

Sorry , made a copy and paste mistake: this is the link:
http://huqixin.blog.dianyuan.com/u/61/1199250649.pdf
Click to expand...
Yes. In that configuration, the MOSFETs can conduct or
block current in either direction.

--
Regards,

John Popelish
 
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 ?
Click to expand...
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
 
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
Click to expand...
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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