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AH_WA70
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Join Date: Mar 2008
Posts: 81

MOSFET

06/14/2009 8:11 AM

I have a MOSFET that is always on and it off only when i give the gate ground and then returns on.Is this is working correctly? if yes i need explaination.
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Anonymous Poster
#1

Re: MOSFET

06/14/2009 11:41 AM

Connect a 1 Kohm resistor from the gate to the ground and if it stays off it is OK. It seems that you either have a sensitive with a low capacitance GS or a very noisy environment.
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AH_WA70
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#2
In reply to #1

Re: MOSFET

06/15/2009 2:56 AM

Thanks for your help
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babybear
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#3
In reply to #2

Re: MOSFET

06/15/2009 3:20 AM

Hello AH WA70,

You may find 'noise' from the steel frame in a concrete flat or house could cause this as well.

bb

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Randall
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#4

Re: MOSFET

06/15/2009 4:52 AM

As I understand it.

An enhancement mode MOSFET is normally off and turns on when you apply the appropriate voltage to the gate.

A depletion mode MOSFET is normally on and turns off when you apply the appropriate voltage to the gate.

I guess you've got a depletion mode device.

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Rorschach
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#5
In reply to #4

Re: MOSFET

06/15/2009 8:47 AM

GA my friend.

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kyilmaz
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Join Date: Jun 2009
Posts: 4
#6

Re: MOSFET

06/18/2009 1:41 AM

You have N channel Mosfet with very little input capacitance.. Therefore input capacitance could be charged through drain to gate and gate to source capacitance and will stay on until gate capacitance is discharged . For that reason it is common practice to create low impedance between gate and source terminal when you do not have control voltage. Simplest way of doing this to connect 10K of lower resistor between these terminal

Kadir Yilmaz

www.globalpowerdesign.com
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AH_WA70
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Posts: 81
#7
In reply to #6

Re: MOSFET

06/22/2009 7:29 AM

Thanks for your help kyalmiz
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