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MOSFET Vgs

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Well that makes more sense. What is the current requirement? If it does not need much all you need is a series resistor.

Dan

Current is 350mA@12V , but Resistance will blow off the moment the high voltage is met with?


Adi
 
Current is 350mA@12V , but Resistance will blow off the moment the high voltage is met with?


Adi
The is a lot for a remote to draw. The crowbar is certainly the simplest, though you will need to replace the fuse when it happens.

You would need to sense the sensor side of the protection for an active cutoff of the type you are talking about, otherwise you get a regulator.

Dan
 
The is a lot for a remote to draw. The crowbar is certainly the simplest, though you will need to replace the fuse when it happens.

You would need to sense the sensor side of the protection for an active cutoff of the type you are talking about, otherwise you get a regulator.

Dan

Yes crowbar May work in time , but i was thinking about a fuseless system as in the process this is pretty common and people dont like to change fuses .

Adi
 
Yes crowbar May work in time , but i was thinking about a fuseless system as in the process this is pretty common and people dont like to change fuses .

Adi
true

you could divide the SMPS output by 6/12 with a filter cap and divide down the other side by 5/12 and put a base emitter junction between them. That way you can switch it off when the higher voltage comes in with out any complex electronics.

Dan
 
true

you could divide the SMPS output by 6/12 with a filter cap and divide down the other side by 5/12 and put a base emitter junction between them. That way you can switch it off when the higher voltage comes in with out any complex electronics.

Dan

I didnt get you when you say "6/12" is this the turn ratio? , and "other side"? or do you mean capacitors in series but I am having DC?

Adi
 
I didnt get you when you say "6/12" is this the turn ratio? , and "other side"? or do you mean capacitors in series but I am having DC?

Adi
No, resistive voltage divider. You have a 12V regulator supplying power to a remote sensor. You are trying to put a power switch in line to protect the regulator.

You want a reference voltage from the power supply side of the switch. Sensing the sensor side of the switch allows the switch to stay off as long as the high voltage remains applied.

Dan
 
I again run into the trap of how to put-on the P-chan mosfet . The Vgs seems to overshoot the moment the Gnd reference gets shifted with over voltage external, condition?


-Adi
 
I again run into the trap of how to put-on the P-chan mosfet . The Vgs seems to overshoot the moment the Gnd reference gets shifted with over voltage external, condition?


-Adi
Look at the arrow in the substrate diode in the spec sheet. The diode needs to block what you want to block. You are effectively creating a synchronous rectifier and if you can afford the loss of less than a volt, it would certainly be easier to just put a fast rectifier in there instead.
 
Look at the arrow in the substrate diode in the spec sheet. The diode needs to block what you want to block. You are effectively creating a synchronous rectifier and if you can afford the loss of less than a volt, it would certainly be easier to just put a fast rectifier in there instead.

What problem is the Ground .
"https://www.electro-tech-online.com/attachments/mos-n-n-2-gif.24626/"

If it works for the normal condition , on over voltage conditions it remains ON too if we use a potential divider , and if we set it for over voltage conditions it remains off for normal conditions. Please explain a bit more where shall we reference the GND , it doesnt looks easy to me a rough schematic would be appretiated.

-Adi
 
like that... as I said, it would be easier just putting a diode in line

I dont get you , this is a schematic I posted earlier please see previous page . The prob is protecting it when the supplies tend to be in series connection this diode will be 0f no use at all. Your potential divider schematic welcomed!


-Adi
 
I dont get you , this is a schematic I posted earlier please see previous page . The prob is protecting it when the supplies tend to be in series connection this diode will be 0f no use at all. Your potential divider schematic welcomed!


-Adi
Did you get the updated version? I crashed in between. The series diodes set up a current source with the transistor, one for the BE junction and one for 0.6V drop across the emitter resistor.

The other thing I was saying was that you could protect the regulator with just a series diode.

Dan
 
Last edited:
Did you get the updated version? I crashed in between. The series diodes set up a current source with the transistor, one for the BE junction and one for 0.6V drop across the emitter resistor.

The other thing I was saying was that you could protect the regulator with just a series diode.

Dan

No I didnt, which updated version?


Adi
 
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