assistance with another ltspice model

Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
Does anyone have a second to see if this model works.
I apparently lack the fundamental understanding of ltspice because I spend more time fighting with the sim then I do gaining knowledge.

I pulled a model for a simple mosfet and yet it will not run as it should.
The VGSth is 2.5 so i should see some conduction at that point. I see none.

model found here

This is a complimentary mosfet pair but i am just using the model for the n chanel.
 

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Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
Out of frustration I changed the amplitude of the sign wave driving the gate to something ridiculous like 500V. It starts to conduct now but this model looks to be totally incorrect. According to the data sheet it should do something at 2.5V vgth
Also, according to the data sheet, the RDS on should be around 3 Ohms at a VGS of 5V
The sim is showing a drain voltage of 1V with a 500V VGSth at 10mA of drain current meaning the RDS on is closer to 100 ohms not 3

What am I doing wrong? I am starting to feel like LTspice is total junk but I know it cant be which only leaves me to be the issue.
So what am I missing?
 

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Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
Also, just for kicks, I discovered that the 2n7002 model exists natively in ltspice.
The native model works as expected with no issue.

So what could I possibly be doing wrong??
 

Audioguru again

Joined Oct 21, 2019
895
A simulation needs an accurate model. You found a model that is wrong.
A simulation shows only a "typical" device, real devices have some better ones and some worse ones.
 

Alec_t

Joined Sep 17, 2013
10,909
Does anyone have a second to see if this model works.
It works fine for me. Are you sure you had the FET the right way up in your schematic?
FETModelTest.png

Edit:
My sim relates only to the PFET. I didn't check the NFET performance.

So what could I possibly be doing wrong?
I've just spotted you apparently have the labels for the FET identifier and FET type transposed. The FET identifier should be, e.g., 'M1' and the NMOS label should read '2N7002'.
 
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Alec_t

Joined Sep 17, 2013
10,909
This is a complementary mosfet pair
Are you sure? The file in the link contains two separate models, for the BSS84 PFET and the 2N7002 NFET respectively.

Edit:
I've just tested the 2nN7002 model from that linked file. It works ok for me.
 
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Thread Starter

MikeJacobs

Joined Dec 7, 2019
95
It works fine for me. Are you sure you had the FET the right way up in your schematic?
View attachment 196224

Edit:
My sim relates only to the PFET. I didn't check the NFET performance.


I've just spotted you apparently have the labels for the FET identifier and FET type transposed. The FET identifier should be, e.g., 'M1' and the NMOS label should read '2N7002'.
I do?
Are you sure?
 
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