N Channel MOSFET Turn On Behaviour

[vaibhavwaman]

Hello,

When I simulated below N channel MOSFET circuit, I observed though MOSFET is connect to ground it starts conducting from Drain to source after ~30V ? why this is happening ?

This MOSFET has 200V VDS breakdown voltage but still it conducts far earlier. Rise time of Drain voltage is also not much high to cause breakdown.

 

[danadakk]

Since your x axis is time are you looking at the trasnsient response due to
MOSFET parasitic C ? Should you be looking at a DC sweep of V ?


Regards, Dana.

 

[dick_freebird]

Weak gate resistor allows drain dV/dt to ramp the gate.

 

[cupoftea]

Yes, as the above noticed....change R47 to zero ohms and notice it doesnt happen so much....but also remember the drain-source capacitance. As the above members have already said.
Google "Spurious FET turn ON" for more info

 

[FvM]

None of the explanations makes sense. You don't turn the transistor on at 1.5 V/ms Vds slope. Cgd related turn on would show in V(U7:G), but there's no significant voltage rise. Initial 20 mV peak is realistic according to Vds slope. Drain current starting at about 30V Vds isn't gate triggered, apparently Vds breakdown.

My assumption: defective model. I don't have a recent PSPICE version with BSC320N20 model. Please post netlist (generated .cir file) and transistor model file.