guys i had spend more times on how to determine the drain current exactly using

the prefer equations , but I failed i think the problem comes from extracting the correct

Kp (constant of mosfet)

any one can put here in details how to calculating + writing the procedures&equations

step by step; please help me find Kp to determine the current i would like

please please ..............etc

extremely; DATASHEET did not including Kp;Ids(on); only they mentioned Rd(on)

WHY;;;;;;;;;;;;;;;;;;;;;;;;;;????????????????????? ???????

ok here my tries :=

IRF510 Datasheet including this INFO:

gfs = 1.3 @ 3.4 A and sometimes in other datasheet 1.3@4 A. & VgsOFF=4V

i do not know what if that gfs is same as Kp or gm ;

i assume it is gm ; thus:

as Id = Kn (Vgs - VgsOFF)^2 .............................. (1)

also

gm = 2 root (Id * Kn) then ---> Kn = (gm)^2 / (4 * Id)

apply this equation yiald: Kn = (1.3)^2 / (4* 3.4) = 124.5 mA/V^2

the required ( given ) parameters are : design MOSFET with Id=10mA with output = 5V

Vdd=9 V ; with using the voltage-divider ... here i want not to includes Rs ( resistor at

source ) .

as Vdd= Vds + Id*Rd

thus Rd= (Vdd - Vds)/ Id = (9-5)/10mA = 400 ohms

at this point all things correct right? theoretically YES yes yes

then as Vgg = Vgs

Vgg = Vdd * (R2/R1+R2) = Vgs

multiply both denominator and divisor by R1/R1 gives :

Vgs = Vdd * Rbb/ R1----------------------- (2)

for MOSFET :

for Id-= 10mA ; assume R1= 10K then

using Equation (1) yiald: Vgs = root(Id/Kn)+VgsOFF = Root(10/124)+4V=4.28 V

Assume R1 =10K

using Equations (2) and solve for Rbb yealds: Rbb = (4.28/9V) * 10K = 4759.9 ohms

and as 1/Rbb = 1/R1 + 1/R2 -----> thus R2 = 1 / ( 1/Rbb - 1/R1) = 1/(1/4759.9 - 1/10K)

thus R2 = 9083 =~ 9K ohms

THE RESULTs :

Id = 10mA

Vgs = 4.28 > VgsOFF (i,e MOSFET is ON )

Id = 10mA @ V0 =5v for Vdd = 9 V

The DISASTERs :

when apply the design on LT-Spice it is not success WHY WHY WHY ....

PLEASE ANYONE GIVE ME AN ANSWERS

YOU HAVE TO LOOK THAT I FORETHOUGHT ( DELIBERATE) NOT TO INCLUDE RS IN MY DESIGN FOR ANALYSIS PURPOSES

SO PLEASE CALCULATE WITHOUT RS