# Help with nmos pspice simulation results

#### 김찬우 1

Joined Oct 8, 2018
11
I already know that this option is for triode mode.

but, i did pspice simulations,

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
21,896
Hello Kim,

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

Bertus

#### 김찬우 1

Joined Oct 8, 2018
11
Oh i didnt notice that. 조건 means condition and 전류식 means equation of ID.

#### bertus

Joined Apr 5, 2008
21,896
Hello,

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

Bertus

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#### 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.

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
15,516
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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#### 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
15,516
hi 1.
Look at this LTspice simulation, VGate sweep from 0v to +6v.
E

EDIT:
Check out this MOSFET PDF covers the 2N7000

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#### 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 :

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

#### ericgibbs

Joined Jan 29, 2010
15,516

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