Help with nmos pspice simulation results

Thread Starter

김찬우 1

Joined Oct 8, 2018
11
I already know that upload_2018-11-3_23-42-48.png this option is for triode mode.

but, i did pspice simulations, upload_2018-11-3_23-44-58.png

upload_2018-11-3_23-45-28.pngupload_2018-11-3_23-45-43.png

and the problem is that first one has - 11.0v of VGD but its cut off mode.(what is at saturation mode according to the equation above)

and the last one has + value of VGD but it is saturation mode. (cause id flows 114.9mA)

its really different from the equation. how can i understand this?
 

bertus

Joined Apr 5, 2008
20,049
Hello Kim,

As this is an english only forum, could you translate the boxed items on your picture:

KIM_2018-11-3_23-42-48.png

Bertus
 

bertus

Joined Apr 5, 2008
20,049
Hello,

Perhaps the characteristics of the 2N7000 (taken from the datasheet) might give you some more insight what is happening:

2N7000_characteristics.png

Bertus
 

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Thread Starter

김찬우 1

Joined Oct 8, 2018
11
thanks, i found that the datasheet is fit the equation i uploaded.

but, i want to know that why my pspice simulations came out that way.

my circuit's id is getting larger as VGD is getting larger.

upload_2018-11-4_0-32-51.png

and second one is triode mode, but the pspice's VGD has - value.(not alien with the equation)
 

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ericgibbs

Joined Jan 29, 2010
8,733
and the problem is that first one has - 11.0v of VGD but its cut off mode
hi 1.

In the first circuit VGate of +1V is below the 2N7000 switch On threshold, so the Drain will be at 12V.
E
 

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Thread Starter

김찬우 1

Joined Oct 8, 2018
11
yeah, that's right. actually cut off mode is decided by only VGS so "and the problem is that first one has - 11.0v of VGD but its cut off mode"

is not the case.
 

ericgibbs

Joined Jan 29, 2010
8,733
hi 1.
Look at this LTspice simulation, VGate sweep from 0v to +6v.
E

AA1 03-Nov-18 15.58.gif

EDIT:
Check out this MOSFET PDF covers the 2N7000
 

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Last edited:

Thread Starter

김찬우 1

Joined Oct 8, 2018
11
after 0.5s it is saturation mode, and the VGD is getting bigger.

but the saturation condition is like this :
upload_2018-11-4_1-8-45.png

i think it has to be getting smaller to satisfy this equation.
 

ericgibbs

Joined Jan 29, 2010
8,733
upload_2018-11-3_16-38-51.png

hi 1,
Put some numerical values in that Equation so that we can your calculations.
E
 
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