initially I also thought same, but doing pratical I had found that it works on 4V though datasheet has given range 0f 2v-4v

hi vp,
When you say datasheet has given range 0f 2v-4v , that is not exactly correct.
It says Vg threshold MIN = 2V , Vg threshold MAX = 4V
This means if you get a batch of MOSFETs of the same type and did a Vgth selection test, you could find that some have a Vgth of as low as 2V and others as high as 4V.. also some of the batch could be 3V and so on.
Also note the Test Conditions, Id=250uA at which Vgth is specified, it is a Very low current.
For your project as you have found you needed to do a Vgth selection test to find a suitable MOSFET

You will find that BJT transistors have the same type of Gain spread, it is due to the spread in manufacturing tolerances.

Hope your project works OK.
E

 

The graphs on a datasheet are for a "typical" one that you might not have. A typical one probably has a threshold Vgs of 3V where it barely turns on and is almost turned off.

 

"This means if you get a batch of MOSFETs of the same type and did a Vgth selection test, you could find that some have a Vgth of as low as 2V and others as high as 4V.. also some of the batch could be 3V and so on. " .... not to mention how temperature might play a roll here as well.

 

SPICE is part of the problem. If Vgth is 2V to 4V then the SPICE model likely was designed for 3V. That being in the center. In the real world you need to design the circuit so a 2V, 3V and 4V transistors all work just fine.

The definition of "on" is another problem. In this case on=250uA. Which is not really on!

Maybe you have a part that turns on the very smallest amount at 3V and is good for 100mA at 4V. If you are switching power then 4V will not work with this transistor. You need to get away from just slightly turned on and give the gate 8, 10 or 12 volts and allow it to handle some real current.

Stop living on the edge and really turn on the transistor.