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problem with grounds

Hello

I posted a simple circuit up on

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I am having difficulty seperating the grounds. My final circuit is much more complex, it may look trivial at first, but I absolutely need to seperate the grounds. IN the simulator they are the same ground. But my 30 v source comes from a separate circuit, therefore do not activate the N-mosfet (no common ground). I need to figure out a way to put 30v on the mosfet so that the rest of the circuit shown sees it and operate the way it is showing. I thought about adding opto couplers, but I will still have the problem of finding 30v on the other side of the circuit to activate the mosfets,( where the maximum volt is 24v). And no I cannot combine the 24v and 12v. anyone has any ideas?

thank you

K
Reply to
lerameur
Loading thread data ...

Optical isolation.

Look for optocouplers.

Below is a good component and many like it.

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the application notes should give you some lead way.

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Reply to
Jamie

If you do that what you have drawn will not work. (but then what you have drawn makes no sense whatsoever) - possibly some of the MOSFETs are backwards?

redraw your circuit so that it is understandable.

put the the parts that are referenced to one ground on one side and those referenced to the other on the other side , and make a line down the middle that indicates where you want isolate it.

M2 and M8 appear to be backwards, only 6v of gate drive is available on M8 is that enough?

To get +30V where you have only +24V stand an isolated 6V supply on top of the 24V supply.

look at using mosfet drivers.

Bye. Jasen

Reply to
Jasen Betts

mode, they can conduct both ways, It works in the simulation

I dont know how much simpler I can put it. I clearly put the two isolation part 'ground 1 and ground 2'

unless I do not understand exactly what you mean.

Also the ground two should not even be there in practice, I just need it in the simulation. I think the HT04 might work, it is driving at high voltage and it has a second output for forcing a reference point. I will try this

K
Reply to
lerameur

mode,

--
If they conduct both ways, how do you turn them off? ;)
Reply to
John Fields

re

ration mode,

o

John,

here is a circuit with reverse mosfet:

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as you can see, they can conduct both ways

here is a circuit when it is turned off

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Those 30 volt supplies on the diagram are actually coming from a separate circuit so it is a circuit like this one:

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hope this is clearer

k
Reply to
lerameur

saturation mode,

--
Not really.

What I meant by: "What are you trying to do, exactly?"

was more like "What\'s your application?"  It sounds like you\'re trying
to PWM a motor in both the forward and reverse directions.  Am I right?

If not, what is it you want to do?

JF
Reply to
John Fields

u

s are

aturation mode,

e to

has

Hi John,

I want to use the mosfet as relays. Once they are switch, the current can flow in either direction. I have a solar panel array with multiple batteries, I am trying to come up with a way with a microcontroller can change only the batteries that are the at their lowest. The whole project is huge, I reduced it down to this circuit, if I can do it on this circuit then what want to do will work.

k
Reply to
lerameur 

--
That\'s not true.

For an "N" channel enhancement mode MOSFET, the gate voltage must be
positive with respect to the source voltage in order for the channel to
be enhanced.  What you\'re seeing if you\'re reversing the polarity of the
supply is charge flowing anode-to-cathode through the internal Zener.
Reply to
John Fields

ng

ht?

e

I will make one by hand, but I will need to be at work to scan and put it in a pdf.

but if you look at design1 Vs design2, I reversed the drain and source and it proves that I am able to conduct both ways, I guess because the mosfet are in saturation in both conditions with the gate at 30v.

wouldn

Reply to
lerameur

but that one's forwards.

no. that image doesn't display.

--

Bye.
   Jasen
Reply to
Jasen Betts 

--
Looks interesting, but I\'ll reserve judgment until I see your block
diagram. :-)

JF
Reply to
John Fields

I just tried the link now, it works, Tell me if its still do not work.

k
Reply to
lerameur

Why do you want to do this? Why not just connect all the batteries in parallel - this will minimised depth-of-discharge on all batteries, and remove a lot of unneeded complexity. Then all batteries will be charged and discharged simultaneously. There is no law requiring you to disconnect all loads from a battery while you are charging it.

--
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
Reply to
Peter Bennett

no. still doesnt work, but I figured out why:.

why do you want 30V on the M6 and M2 gates, 22V should be enough on M6 and 10V on M2

why do you need M8 at all? can you move it?

Reply to
Jasen Betts

Hi all, John,

here is a working schematic with opto couplers. Basically this circuit is not fully functional because it do not fully open the mosfet and not allowing all the current to go through. I thought of adding the tc4432 buffers instead of the opto coupler, but I had the grounding problem. With the optocoupler I was taking the voltage of the batteries as the reference point, but it does not allow me for enough gate voltage. so basically this circuit:

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but a higher gate voltage. is this more clear?

k
Reply to
lerameur

this looks like a circuit designed to destroy mosfets and/or optocouplers.

what current does your simulations suggest would be flowing.

I suggest you add some series resistors to the input side of the optocouplers. about 220 ohms would be good I think.

the batteries are connected in what seems like an unusual setup,

the 5 ohm resistor you had in the loop last time is gone now.

Bye. Jasen

Reply to
Jasen Betts

.

I did not put the resistor in the last circuit, I should of.

Ok here I have three circuit:

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The first is with a 12v at the gate, then 20 and 25, the 30v circuit was in my first link. I noticed that beyond 30v the mosfet is already in saturation and will not conduct more. This is why I need 30v. I just want to know how to put 30v on these gates when the ground is NOT a common ground. Is it possible? I am looking to redesign, unless someone tells me it is impossible and really need to redesign.

thanks k

Reply to
lerameur

.

I did not put the resistor in the last circuit, I should of.

Ok here I have three circuit:

formatting link
The first is with a 12v at the gate, then 20 and 25, the 30v circuit was in my first link. I noticed that beyond 30v the mosfet is already in saturation and will not conduct more. This is why I need 30v. I just want to know how to put 30v on these gates when the ground is NOT a common ground. Is it possible? I am not looking to redesign, unless someone tells me it is impossible and really need to redesign.

(BTW, the ground in the simulation are there because they are need during the simulation, otherwise pspice it will not run) thanks k

Reply to
lerameur

Jamie wrote in news:y1hBk.25806$ snipped-for-privacy@newsfe04.iad:

I'm gettign "file not found" - I also qwent to the site and searched D26, but that didn't work. Could you post the component name, or another search term I could use...?

Thanks!

Reply to
Kris Krieger

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