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MOSFET draws very little current ?

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rajesh.kmr

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MOSFET have high input resistance. How is this possible to draw very little current ?
 

MOSFET´s are voltage controlled components.

In MOSFETs, a voltage on the oxide-insulated gate electrode can induce a conducting channel between the two other contacts called source and drain. The channel can be of n-type or p-type (see article on semiconductor devices), and is accordingly called an nMOSFET or a pMOSFET (also commonly nMOS, pMOS). It is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common.

The gate lies on an insulated thin oxide layer (dielectric) above the substrate between the source and drain. The gate is effectively one side of a capacitor. This is the input impedance being referred to - the fact that the gate has no DC path to either source, drain or substrate.

MOSfet_Pic_01.jpg

MOSFET - Wikipedia, the free encyclopedia
 

Dear Friends!
Hi
At Dc voltages as vgs of mosfets , the input current will be about zero (estimated). and according to the name of mosfet( metal oxide semiconductor field effect transistor) the width of channel will control by vgs but with magnetic flux (magnetic fields) . thus we will not need current as a driving current .
But at high frequencies ( pulse signal as vgs) we will have current at gs . but not current to the infinite resistance of mosfet . the mosfet ( its gs) has an capacitor (parasitic) . at high frequencies , its XC will decrease and thus we will have current as gate current.
Best Wishes
Goldsmith
 

Hmmm... Hall effect MOSFETs ??

The depletion region was controlled by electrical charge, not magnetic fields when I was at school. Mind you, that was a long time ago!

Brian.
 

Dear Brian
Hi
Thanks for your attention.
But if you refer to the name of mosfet ( metal oxide field effect transistor) =field effect ! you can know that what is my mean.
and if we have the electrical charge , (like a simple capacitor) the charges have fields too!
Best Regards
Goldsmith
 

for clarity
refresher ..... fet operating principle


The FET operates by the effects of an electric field on the flow of electrons through a single type of semiconductor material.
Current moves within the FET in a channel, from the source connection to the drain connection. A gate terminal generates an electric field that controls the current . The channel is made of either N-type or P-type semiconductor material; an FET is specified as either an N-channel or P-channel device. Majority carriers flow from source to drain.


A metal–oxide–semiconductor field-effect transistor (MOSFET) is based on the modulation of charge concentration by a MOS capacitance between a body electrode and a gate electrode located above the body and insulated from all other device regions

If the MOSFET is an n-channel or nMOS FET, then the source and drain are 'n+' regions and the body is a 'p' region. As described above, with sufficient gate voltage, holes from the body are driven away from the gate, forming an inversion layer or n-channel at the interface between the p region and the oxide. This conducting channel extends between the source and the drain, and current is conducted through it when a voltage is applied between source and drain. Increasing the voltage on the gate leads to a higher electron density in the inversion layer and therefore increases the current flow between the source and drain.

If the MOSFET is a p-channel or pMOS FET, then the source and drain are 'p+' regions and the body is a 'n' region. When a negative gate-source voltage (positive source-gate) is applied, it creates a p-channel at the surface of the n region, analogous to the n-channel case, but with opposite polarities of charges and voltages. When a voltage less negative than the threshold value (a negative voltage for p-channel) is applied between gate and source, the channel disappears and only a very small subthreshold current can flow between the source and the drain.
 

Dear brian
Hi
You said that it is with electrical charge . but i said with magnetic field . i know that in fact it is not correct . and it is electrical field. but my mean was just field . but i don't said that i'm disagree with you. i agree with field !
Again thanks for your attention .
Best Regards
Goldsmith
 

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