How can I use n- enhancement MOSFET as a switch??? (THANKS)

Please look at the circuit

How can I use HIGH/ LOW to control the MOSFET to ON/OFF??

i.e

1)If Gate >5V.........the path between drain and source = close circuit
the load is come to vdd


2)If Gate =0V.........the path between drain and source = open circuit

Thanks

Re: How can I use n- enhancement MOSFET as a switch??? (THAN

generally the high/low signal should be such that the mosfet completely turns on/off.....

it is taken care that the source voltage is high enough not to cause problem during on state....

if the 0V/5V switching is not enough then use a comparator which has a larger swing....

Re: How can I use n- enhancement MOSFET as a switch??? (THAN

No it wont work your source is at Vdd potential, your gate for a logic level FET needs in this case Vdd + 5V for full enhancement. Flip your FET around, and look for a high side driver. You could also try using a p-channel FET; I don’t know the rest of your cct, what voltages you have available.

A mosfet is a voltage controlled device but you also have to consider, that the speed in which it can switch is related to the peak current into the gate.For example say your mosfets Qg (this is in the data sheet) is 10nC,your are looking at a driver that can source 0.5A at your Vcc.Then your mosfets rise time can be estimated by simply:

tr = Qg/Ipk
= 10nS/0.5A
= 20nS

Its usually a bit higher then this but it gets you in the ballpark.
There are other considerations but they can be answered by reading a few high side driver application notes.

Good luck

Re: How can I use n- enhancement MOSFET as a switch??? (THAN

first of all the source hav been connected to vdd, u can refer to kang for this problem