# [SOLVED]Why doesn't this simple circuit work in simulation?

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#### AlienCircuits

##### Member level 5
I expect the switch to turn on and conduct when Vgs = 15V, which is the pulse I'm sending to the gate. However, the switch seems to always be off.

#### goldsmith

Hi Alien
At first why 100 k ohms in drain ? it is too high for switching applications ! decrease it as 1 k ohms or 560 ohms . how much is frequency of your pulses ?
Best Wishes
Goldsmith

#### AlienCircuits

##### Member level 5
Hi Alien
At first why 100 k ohms in drain ? it is too high for switching applications ! decrease it as 1 k ohms or 560 ohms . how much is frequency of your pulses ?
Best Wishes
Goldsmith

The 100k ohms is because the supply voltage is 1000V and the MOSFET is only rated for .2A.

The frequency is 50Hz.

I tried your suggestions, changing the resistor to 560 Ohm, and I get the same simulation plot. So it still does not switch.

#### goldsmith

Tell me your frequency , thus i can simulate it , perhaps i could earn success !

#### AlienCircuits

##### Member level 5
My pulses are 50Hz.

Here is the model:
* PSpice Model Editor - Version 9.2.1
*$.SUBCKT IXTP02N120P G D S ********************************************************************* *Note: * * Althought models can be a useful tool in evaluating device * * performance, they cannot model exact device performance * * under all conditions, nor are they intended to replace * * bread boarding for final verification. Therefore IXYS does * * not assume any liability arsing from their use. IXYS reserves * * the right to change models without prior notice. The Pspice model * * does not constitute product data sheet. Designer should refer to * * the data sheet to guranteed the limit and specification. * ********************************************************************* ** model generated on August 31, 2012 * Node 1 -> Drain * Node 2 -> Gate * Node 3 -> Source M110 D G S1 S1 MM111 L_s S S1 1n .MODEL MM111 NMOS + LEVEL=3 + L=2.0000E-6 + W=.33 + KP=1.0331E-6 + RS=10.000E-3 + RD=59.148 + VTO=2.9879 + RDS=1.2000E9 + TOX=2.0000E-6 + CGSO=191.89E-12 + CGDO=16.167E-12 + CBD=191.99E-12 + MJ=1.4624 + PB=1.5310 + RG=10.000E-3 + RB=1.0000E-3 + GAMMA=0 + KAPPA=0 * L_bd S2 S 1n D_1 S2 D BD .MODEL BD D + IS=3.0108E-16 + N=2.7849 + RS=1.0000E-3 + CJO=1.0000E-12 + M=.3333 + VJ=.75 + ISR=10.010E-21 + BV=1.1999E3 + IBV=25.890E-3 + TT=28.793E-6 .ENDS *$

#### goldsmith

I have simulated it with another mosfet and 500 volts ! see below , please : ( i think you didn't measure voltage of drain ! perhaps you have putted the probe on VDC ?)

Good luck
Goldsmith

AlienCircuits

### AlienCircuits

Points: 2

#### AlienCircuits

##### Member level 5
I have simulated it with another mosfet and 500 volts ! see below , please : ( i think you didn't measure voltage of drain ! perhaps you have putted the probe on VDC ?)

Good luck
Goldsmith

No, I have measured the voltage at the drain. The netname shows up in my first circuit picture, and that is the name in the simulation plot too. Your simulation shows what I expected to see with my circuit, but my circuit doesn't do this :/

Perhaps my MOSFET model is incorrect? I had to request it in email from the manufacturer.

#### goldsmith

Perhaps my MOSFET model is incorrect?
Perhaps !
Best Luck
Goldsmith

AlienCircuits

### AlienCircuits

Points: 2

#### keith1200rs

##### Super Moderator
Staff member
It is a defective Spice model. Edit the first line of the model to be

.SUBCKT IXTP02N120P D G S

then it works.

Keith.

AlienCircuits

### AlienCircuits

Points: 2

#### AlienCircuits

##### Member level 5
I figured out the problem! Thanks goldsmith, you helped me because I am not confident with MOSFETs yet and I wasn't sure if what I saw was incorrect. You verified my thoughts, and so I checked the model.
They created the model non-standard, with the Drain and Gate order swapped. I fixed it and it simulations correctly.

Thank you.

- - - Updated - - -

It is a defective Spice model. Edit the first line of the model to be

.SUBCKT IXTP02N120P D G S

then it works.

Keith.

Hehe, I just found that out and came here to read this

#### keith1200rs

##### Super Moderator
Staff member
You did well to find it. Fixing companies cr@ppy models is not easy. You always assume they have tested them and that you are making a mistake!

Keith.

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