MOSFET Confusion. Please Help

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Popee

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Hi all,
Im getting a little bit confused as to which mosfet I need. I want it to act with the same 'turn' on characteristics as an NPN Bi-polar transistor.

E.G High resistance when no voltage is applied to the gate and then a low resistance when a positive voltage is applied to the gate

I thought the correct MOSFET to choose was a N Type Mosfet with Enhancement. Can anyone clear this up for me?

regards, Lee S
 

yes, you are right. you can use a NMOS transitor
 


Hello, Yes you need N type. I think the reason of your confusion is the point that you measure your voltage in reference to that. in bipolar npn if voltage base to emitter is 0 then collector will be high Z. in Mosfet N channel if gate to source voltage be 0 then drain will be High Z and when you give a voltage to gate more positive than threshold voltage of mosfet in reference to source(this threshold voltage is different for each mosfet) then impedance of channel(drain to source) will be decreased. more positive less impedance until you reach a plateau. read datasheet of an N-Mosfet and look at graphs. it will be clear to you.
good luck
 

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