mosfet 2 questions????

[mahsa]

1)why in enhancement mosfet we say that if Vgs=0 and Vds is increasing the depletion area increases more around the Drain?
2)why we say (Ig=0) in enhancement mosfets?in Jfets it is clear but in E-mosfets we had two back2back diodes that Gate is located between them so the P-N junction is not in Reverse Bias

 

[trobbins]

What reference books or papers or application notes do you have on enhancement mosfets? I guess you have found some app notes at IRF ?

 

[(*steve*)]

1) Consider the effect of gate voltage on the depletion region. If Vgs is 0, and Vds is not 0, what is Vgd, and what effect might that have?

2) I think you are confusing mosfets and bipolar transistors. look again at the construction of the gate electrode and consider an almost synonymous acronym: IGFET

 

[mahsa]

2)yeah I figured it out.it was because of the role of gate as a capacitor that in small signal is equal to open-circuit.thanx for ur help
1)in this condition Vgd is negative which shows that Drain does have more potential than Gate.but the main carriers are electrons so Drain will collect more electrons.so what will happen the next????

 

[trobbins]

(2) check your understanding of the gate-source and gate-drain as voltage-dependant capaitances, where Vgs controls Ids. The only time Ig is not zero for a capaitor is ....